Following on from the comments by MITs Carl Wunsch that the Gulf Stream is safe as long as the wind blows and the Earth turns, several other scientists have used the pages of Science magazine (Apr. 16) to pour scorn on the conceit behind the forthcoming movie, The Day After Tomorrow.  The movie is predicated on the idea that unchecked global warming will cause an abrupt climate shift that will cause a new ice age in the United States.

Canadian scientists Andrew Weaver of the University of Victoria and Claude Hillaire-Marcel of the Universit de Quebec Montreal tackled the subject in a Perspectives article entitled, Global Warming and the Next Ice Age.  They pointed out that the view of global warming causing an ice age prevails in the popular press despite a relatively solid understanding of glacial inception and growth.

The scientists review of the literature concluded that, It is certainly true that if the AMO [Atlantic Meriodonal Oscillation] were to become inactive, substantial short-term cooling would result in western Europe, especially during the winter.  However, it is important to emphasize that not a single coupled model assessed by the 2001 IPCC Working Group I on Climate Change Science (4) predicted a collapse in the AMO during the 21st century.  Even in those models where the AMO was found to weaken during the 21st century, there would still be warming over Europe due to the radiative forcing associated with increased levels of greenhouse gases.

Pointing out that models that do show AMO collapse are not flux-adjusted like newer models, they conclude, Even the recent observations of freshening in the North Atlantic (a reduction of salinity due to the addition of freshwater) appear to be consistent with the projections of perhaps the most sophisticated nonflux adjusted model.  Ironically, this model suggests that such freshening is associated with an increased AMO (16).  This same model proposes that it is only Labrador Sea Water formation that is susceptible to collapse in response to global warming.

In light of the paleoclimate record and our understanding of the contemporary climate system, it is safe to say that global warming will not lead to the onset of a new ice age.  These same records suggest that it is highly unlikely that global warming will lead to a widespread collapse of the AMOdespite the appealing possibility raised in two recent studiesalthough it is possible that deep convection in the Labrador Sea will cease.  Such an event would have much more minor consequences on the climate downstream over Europe.

In the same issue, pioneering oceanographer Wallace Broecker dismisses the recent report rejected by the Pentagon that is predicated on a similar scenario.  He comments in his letter, Exaggerated scenarios serve only to intensify the existing polarization over global warming.

The George C. Marshall Institute will host two briefings by Dr. David Legates, director of the University of Delawares Center for Climatic Research, speaking on “Global Warming and the Hydrologic Cycle: How is the Occurrence of Floods, Droughts, and Storms Likely to Change?” The first is at noon on Monday, April 12, in Room 406 of the Senate Dirksen Office Building. The second begins at noon on Wednesday, April 14, in Room 2325 of the Rayburn House Office Building. Lunch is provided. Reservations are required and may be made by phoning (202) 296-9655 or by e-mail to info@marshall.org.

Comments needed: The U. S. Climate Change Science Program is inviting interested parties to provide comments on the draft guidelines for the synthesis and assessment products that are being prepared by the Program to “support both policymaking and adaptive management.” Comments are due by May 3. See www.climatescience.gov for further details.

Energy Bill Prompts Rash of Proposals

The Senate energy bill, S. 14, when published in draft form contained a climate change title. Three specific provisions raised alarm bells for many the requirement for a national strategy to “stabilize and over time reduce net U.S. emissions of greenhouse gases,” including annual reports; a revival of the Clinton-Gore Administrations White House climate czar and office; and a program to award credits for early action in reducing emissions.

Following protests against the title, such as a letter to Sen. Pete Domenici (R.N.M.), Chairman of the Committee on Energy and Natural Resources and sponsor of the bill, signed by representatives of 21 nonprofit organizations including members of the Cooler Heads Coalition, the title was dropped from the draft bill. Nor does the bill contain any reference to a higher CAFE standard, a Renewable Portfolio Standard for utilities, or an expanded ethanol mandate.

These omissions have led to a rash of proposed amendments. The Environment and Public Works committee has passed out an ethanol mandate similar to last year’s 5 billion gallon per year mandate with some slight improvements. The mandate will ban the current most popular additive MTBE, which has been accused of contaminating groundwater. Ethanol, however, has environmental problems of its own, as more emissions are generated in the production of the added ethanol than in the burning of the gasoline it replaces. Sens. Schumer, Clinton, Feinstein, and Boxer have signaled that they will again try to defeat the ethanol mandate, but are unlikely to succeed.

The Senate is scheduled to resume floor debate on the bill on Monday 2 June and will continue debate throughout the week. Several Senators are likely to propose amendments reinstating climate change provisions to the bill. It is probable that the Energy and Natural Resources Committees ranking Democrat, Sen. Jeff Bingaman (D.N.M.), will offer language similar to that approved in Titles X, XI and XIII in last years Energy bill sponsored by Sen. Tom Daschle (D.S.D.).

Other possibilities include climate change proposals sponsored by Sens. McCain, Lieberman, Jeffords, Carper, Gregg and possibly others. Any proposal to raise Corporate Average Fuel Economy Standards for automobiles is likely to be defeated following last years lopsided vote against them.

Further developments will be featured in the next newsletter.

The House Resources Committee held a field hearing in Saint Clairsville, Ohio on May 13 on the potential economic effects of Kyoto-style policies on coal-dependent communities. A bleak future for Ohios coal communities if CO2 emissions are limited was described in testimony by Robert Murray, a major independent coal producer, Eugene Trisko, representing the United Mine Workers of America, Gary Obloy of the Community Action Commission of Belmont County, and others.

Dr. John Christy, Professor of Atmospheric Science and Director of the Earth System Science Center at the University of Alabama in Huntsville, described the shaky scientific basis for global warming alarmism. He then widened the discussion of the negative social and economic effects of energy-rationing policies by drawing on his experiences as a missionary in east Africa.

Christy expanded on his comments in a May 22 letter to the chairman of the Resources Committee, Rep. Richard Pombo (R.Calif.), in which he wrote:

“I’ve always believed that establishing a series of coal-fired power plants in countries such as Kenya (with simple electrification to the villages) would be the best advancement for the African people and the African environment.

“An electric light bulb, a microwave oven and a small heater in each home would make a dramatic difference in the overall standard of living. No longer would a major portion of time be spent on gathering inefficient and toxic fuel. The serious health problems of hauling heavy loads and lung poisoning would be much reduced.

“Women would be freed to engage in activities of greater productivity and advancement. Light on demand would allow for more learning to take place and other activities to be completed. Electricity would also foster a more efficient transfer of important information from radio or television. And finally, the preservation of some of the most beautiful and diverse habitats on the planet would be possible if wood were eliminated as a source of energy.

“Providing energy from sources other than biomass (wood and dung), such as coal-produced electricity, would bring longer and better lives to the people of the developing world and greater opportunity for the preservation of their natural ecosystems.

“Let me assure you, notwithstanding the views of extreme environmentalists, that Africans do indeed want a higher standard of living. They want to live longer and healthier with less burden bearing and with more opportunities to advance.

“New sources of affordable, accessible energy would set them down the road of achieving such aspirations. These experiences made it clear to me that affordable, accessible energy was desperately needed in African countries.

“As in Africa, ideas for limiting energy use…create the greatest hardships for the poorest among us. As I mentioned in the Hearing, enacting any of these noble-sounding initiatives to deal with climate change through increased energy costs, might make a wealthy urbanite or politician feel good about themselves, but they would not improve the environment and would most certainly degrade the lives of those who need help now.”

Following Americas decision not to move forward with the Kyoto Protocol, environmentalist attention has switched to Russia, as the protocol cannot become international law without Russian ratification. Russia had been expected to ratify the protocol this year as its ailing economy had already met emissions targets thanks to the forced closure of so many emissions sources.

However, following several years of strong economic growth, moves to ratify the protocol have slowed. German Gref, Minister for Economic Development and Trade, has been accused by the World Wildlife Fund of blocking ratification by failing to move the process forward. Speaking at the G8 meeting at the end of April, the junior Minister for Natural Resources, Irina Ossokina told Agence France Presse, “I would like to underline that we at the Ministry of Natural Resources are wholly and truly for the ratification of the Kyoto Protocol but unfortunately we have a difference of opinion within the country We were hoping to ratify this summer but we were having difficulties with our economic advisors.”

Meanwhile, Russian scientists are playing a large role in organizing a major International Conference on Climate Changes, scheduled to take place in Moscow this fall. The chair of the conference, Yuriy Izrael, told Russian reporters, “We are looking forward to serious, interesting discussions We are not going to create new contradictions but … find out what is really going on on this planet - warming or cooling.”

Izrael went on to say, “The most important issue, whether [ratifying the Kyoto Protocol] will bring about an improvement of the climate or its stabilization, or its worsening, is not clear.” (AFP, April 27, St Petersburg Times, 13 May).

Many children have been taught to fear the supposedly imminent arrival of global warming even though no one really knows if the world is getting hotter. While it is important to make children aware that current scientific evidence is inconclusive, it also may be helpful to put to rest some of the irrational fears of global warming. Facts, Not Fear, a guide book on teaching children about the environment by Jane Shaw and Michael Sanera, offers several suggestions.

• First, they suggest teaching children about dinosaurs. Ask children to describe the environment the dinosaurs lived in, including the vegetation, and ask them if the world was warmer or cooler than it is now. Explain to them that at the time dinosaurs lived the atmosphere had CO2 levels that were at least 5 times greater than what we now have and that these high levels of CO2 contributed to the rich vegatation.
  
• The book also suggests a field trip to a greenhouse to learn about the “greenhouse effect.” Ask the greenhouse manager to explain how the conditions in the greenhouse are controlled to help plants and ask if the greenhouse adds carbon dioxide. Many greenhouses do add CO2 because it is a vital component of photosynthesis. This can help children learn that CO2 isn’t the dangerous gas that it is often portrayed as.
  
• Finally, Sanera and Shaw suggest teaching children about former predictions of a coming ice age. Have children read articles and books such as “The Ice Age Cometh?” from Time in January 31, 1994, The Cooling by Lowell Ponte, and “Brace Yourself for Another Ice Age,” from Science Digest in February of 1975.
  

Please note that this glossary was compiled with defininitions from the United States Environmental Protection Agency.

Absorption of Radiation. The uptake of radiation by a solid body, liquid or gas. The absorbed energy may be transferred or re-emitted.

Acid Rain. Also known as “acid deposition.” Acidic aerosols in the atmosphere are removed from the atmosphere by wet deposition (rain, snow, fog) or dry deposition (particles sticking to vegetation). Acidic aerosols are present in the atmosphere primarily due to discharges of gaseous sulfur oxides (sulfur dioxide) and nitrogen oxides from both anthropogenic and natural sources. In the atmosphere these gases combine with water to form acids.

Aerosols. Particles of matter, solid or liquid, larger than a molecule but small enough to remain suspended in the atmosphere. Natural sources include salt particles from sea spray and clay particles as a result of weathering of rocks, both of which are carried upward by the wind. Aerosols can also originate as a result of human activities and in this case are often considered pollutants. See also Sulfate Aerosols.

Albedo. The ratio of reflected to incident light; albedo can be expressed as either a percentage or a fraction of 1. Snow covered areas have a high albedo (up to about 0.9 or 90%) due to their white color, while vegetation has a low albedo (generally about 0.1 or 10%) due to the dark color and light absorbed for photosynthesis. Clouds have an intermediate albedo and are the most important contributor to the Earth’s albedo. The Earth’s aggregate albedo is approximately 0.3.

Alliance of Small Island States (AOSIS). The group of Pacific and Caribbean nations who call for relatively fast action by developed nations to reduce greenhouse gas emissions. The AOSIS countries fear the effects of rising sea levels and increased storm activity predicted to accompany global warming. Its plan is to hold Annex I Parties to a 20 percent reduction in carbon dioxide emissions by the year 2005.

Annex I Parties. Industrialized countries that, as parties to the Framework Convention on Climate Change, have pledged to reduce their greenhouse gas emissions by the year 2000 to 1990 levels. Annex I Parties consist of countries belonging to the Organization for Economic Cooperation and Development (OECD) and countries designated as Economies-in-Transition.

Anthropogenic. Derived from human activities.

Atmosphere. The mixture of gases surrounding the Earth. The Earth’s atmosphere consists of about 79.1% nitrogen (by volume), 20.9% oxygen, 0.036% carbon dioxide and trace amounts of other gases. The atmosphere can be divided into a number of layers according to its mixing or chemical characteristics, generally determined by its thermal properties (temperature). The layer nearest the Earth is the troposphere, which reaches up to an altitude of about 8 km (about 5 miles) in the polar regions and up to 17 km (nearly 11 miles) above the equator. The stratosphere, which reaches to an altitude of about 50 km (31 miles) lies atop the troposphere. The mesosphere which extends up to 80-90 km is atop the stratosphere, and finally, the thermosphere, or ionosphere, gradually diminishes and forms a fuzzy border with outer space. There is relatively little mixing of gases between layers.

Baseline Emissions. The emissions that would occur without policy intervention (in a business-as-usual scenario). Baseline estimates are needed to determine the effectiveness of emissions reduction programs (often called mitigation strategies).

Berlin Mandate. A ruling negotiated at the first Conference of the Parties (CoP 1), which took place in March, 1995, concluding that the present commitments under the Framework Convention on Climate Change are not adequate. Under the Framework Convention, developed countries pledged to take measures aimed at returning their greenhouse gas emissions to 1990 levels by the year 2000. The Berlin Mandate establishes a process that would enable the Parties to take appropriate action for the period beyond 2000, including a strengthening of developed country commitments, through the adoption of a protocol or other legal instruments.

Biogeochemical Cycle. The chemical interactions that take place among the atmosphere, biosphere , hydrosphere, and geosphere.

Biomass. Organic nonfossil material of biological origin. For example, trees and plants are biomass.

Biomass Energy. Energy produced by combusting renewable biomass materials such as wood. The carbon dioxide emitted from burning biomass will not increase total atmospheric carbon dioxide if this consumption is done on a sustainable basis (i.e., if in a given period of time, regrowth of biomass takes up as much carbon dioxide as is released from biomass combustion). Biomass energy is often suggested as a replacement for fossil fuel combustion which has large greenhouse gas emissions.

Biosphere. The region on land, in the oceans, and in the atmosphere inhabited by living organisms.

Borehole. Any exploratory hole drilled into the Earth or ice to gather geophysical data. Climate researchers often take ice core samples, a type of borehole, to predict atmospheric composition in earlier years.

Carbon Cycle. The global scale exchange of carbon among its reservoirs, namely the atmosphere, oceans, vegetation, soils, and geologic deposits and minerals. This involves components in food chains, in the atmosphere as carbon dioxide, in the hydrosphere and in the geosphere.

Carbon Dioxide (CO₂). The greenhouse gas whose concentration is being most affected directly by human activities. CO₂ also serves as the reference to compare all other greenhouse gases (see carbon dioxide equivalents). The major source of CO₂ emissions is fossil fuel combustion. CO₂ emissions are also a product of forest clearing, biomass burning, and non-energy production processes such as cement production. Atmospheric concentrations of CO₂ have been increasing at a rate of about 0.5% per year and are now about 30% above preindustrial levels.

Carbon Dioxide Equivalent (CDE). A metric measure used to compare the emissions from various greenhouse gases based upon their global warming potential (GWP). Carbon dioxide equivalents are commonly expressed as “million metric tons of carbon dioxide equivalents (MMTCDE)” or “million short tons of carbon dioxide equivalents (MSTCDE)” The carbon dioxide equivalent for a gas is derived by multiplying the tons of the gas by the associated GWP.

For example, the GWP for methane is 24.5. This means that emissions of one million metric tons of methane is equivalent to emissions of 24.5 million metric tons of carbon dioxide. Carbon may also be used as the reference and other greenhouse gases may be converted to carbon equivalents. To convert carbon to carbon dioxide, multiply the carbon by 44/12 (the ratio of the molecular weight of carbon dioxide to carbon).

Carbon Equivalent (CE). A metric measure used to compare the emissions of the different greenhouse gases based upon their global warming potential (GWP). Greenhouse gas emissions in the U.S. are most commonly expressed as “million metric tons of carbon equivalents” (MMTCE). Global warming potentials are used to convert greenhouse gases to carbon dioxide equivalents. Carbon dioxide equivalents can then be converted to carbon equivalents by multiplying the carbon dioxide equivalents by 12/44 (the ratio of the molecular weight of carbon to carbon dioxide). Thus, the formula to derive carbon equivalents is:

Carbon Sequestration. The uptake and storage of carbon. Trees and plants, for example, absorb carbon dioxide, release the oxygen and store the carbon. Fossil fuels were at one time biomass and continue to store the carbon until burned.

Carbon Sinks. Carbon reservoirs and conditions that take in and store more carbon (carbon sequestration) than they release. Carbon sinks can serve to partially offset greenhouse gas emissions. Forests and oceans are common carbon sinks.

Chlorofluorocarbons and Related Compounds. This family of anthropogenic compounds includes chlorofluorcarbons (CFCs), bromofluorcarbons (halons), methyl chloroform, carbon tetrachloride, methyl bromide, and hydrochlorofluorcarbons (HCFCs). These compounds have been shown to deplete stratospheric ozone, and therefore are typically referred to as ozone depleting substances. The most ozone-depleting of these compounds are being phased out under the Montreal Protocol.

Climate. The average weather (usually taken over a 30-year time period) for a particular region and time period. Climate is not the same as weather, but rather, it is the average pattern of weather for a particular region. Weather describes the short-term state of the atmosphere. Climatic elements include precipitation, temperature, humidity, sunshine, wind velocity, phenomena such as fog, frost, and hail storms, and other measures of the weather.

Climate Change (also referred to as ‘global climate change’). The term ‘climate change’ is sometimes used to refer to all forms of climatic inconsistency, but because the Earth’s climate is never static, the term is more properly used to imply a significant change from one climatic condition to another. In some cases, ‘climate change’ has been used synonymously with the term, ‘global warming’; scientists however, tend to use the term in the wider sense to also include natural changes in climate. See also Enhanced Greenhouse Effect.

Climate Change Action Plan (). Unveiled in October, 1993 by President Clinton, the CCAP is the U.S. plan for meeting its pledge to reduce greenhouse gas emissions under the terms of the Framework Convention on Climate Change (FCCC). The goal of the CCAP is to reduce U.S. emissions of anthropogenic greenhouse gases to 1990 levels by the year 2000. The CCAP, which consists of some 50 voluntary federal programs that span all sectors of the economy, uses a win-win approach by helping program partners save energy, save money, and gain access to clean technology while also reducing greenhouse gas emissions.

Climate Feedback. An atmospheric, oceanic, terrestrial, or other process that is activated by the direct climate change induced by changes in radiative forcing. Climate feedbacks may increase (positive feedback) or diminish (negative feedback) the magnitude of the direct climate change.

Climate Lag. The delay that occurs in climate change as a result of some factor that changes only very slowly. For example, the effects of releasing more carbon dioxide into the atmosphere may not be known for some time because a large fraction is dissolved in the ocean and only released to the atmosphere many years later.

Climate Model. A quantitative way of representing the interactions of the atmosphere, oceans, land surface, and ice. Models can range from relatively simple to quite comprehensive. Also see General Circulation Model.

Climate Modeling. The simulation of the climate using computer-based models. Also see General Circulation Model.

Climate Sensitivity. The equilibrium response of the climate to a change in radiative forcing; for example, a doubling of the carbon dioxide concentration.

Climate System (or Earth System). The atmosphere, the oceans, the biosphere, the cryosphere, and the geosphere, together make up the climate system.

Cogeneration. The process by which two different and useful forms of energy are produced at the same time. For example, while boiling water to generate electricity, the leftover steam can be sold for industrial processes or space heating.

Compost. Decayed organic matter that can be used as a fertilizer or soil additive.

Conference of the Parties (CoP). The CoP is the collection of nations which have ratified the Framework Convention on Climate Change (FCCC), currently over 150 strong, and about 50 Observer States. The primary role of the CoP is to keep the implementation of the Convention under review and to take the decisions necessary for the effective implementation of the Convention. The first CoP (CoP 1) took place in Berlin from March 28th to April 7th, 1995, and was attended by over 1000 observers and 2000 media representatives.

Cryosphere. The frozen part of the Earth’s surface. The cryosphere includes the polar ice caps, continental ice sheets, mountain glaciers, sea ice, snow cover, lake and river ice, and permafrost.

Deforestation. Those practices or processes that result in the change of forested lands to non-forest uses. This is often cited as one of the major causes of the enhanced greenhouse effect for two reasons: 1) the burning or decomposition of the wood releases carbon dioxide; and 2) trees that once removed carbon dioxide from the atmosphere in the process of photosynthesis are no longer present and contributing to carbon storage.

Desertification. The progressive destruction or degradation of existing vegetative cover to form desert. This can occur due to overgrazing, deforestation, drought, and the burning of extensive areas. Once formed, deserts can only support a sparse range of vegetation. Climatic effects associated with this phenomenon include increased albedo, reduced atmospheric humidity, and greater atmospheric dust (aerosol) loading.

El Nino. A climatic phenomenon occurring irregularly, but generally every 3 to 5 years. El Ninos often first become evident during the Christmas season (El Nino means Christ child) in the surface oceans of the eastern tropical Pacific Ocean. The phenomenon involves seasonal changes in the direction of the tropical winds over the Pacific and abnormally warm surface ocean temperatures. The changes in the tropics are most intense in the Pacific region, these changes can disrupt weather patterns throughout the tropics and can extend to higher latitudes, especially in Central and North America. The relationship between these events and global weather patterns are currently the subject of much research in order to enhance prediction of seasonal to interannual fluctuations in the climate.

Emissions. The release of a substance (usually a gas when referring to the subject of climate change) into the atmosphere.

Enhanced Greenhouse Effect. The natural greenhouse effect has been enhanced by anthropogenic emissions of greenhouse gases. Increased concentrations of carbon dioxide, methane, and nitrous oxide, CFCs, HFCs, PFCs, SF6, NF3, and other photochemically important gases caused by human activities such as fossil fuel consumption and adding waste to landfills, trap more infra-red radiation, thereby exerting a warming influence on the climate. See Climate Change and Global Warming.

Evapotranspiration. The sum of evaporation and plant transpiration. Potential evapotranspiration is the amount of water that could be evaporated or transpired at a given temperature and humidity, if there was plenty of water available. Actual evapotranspiration can not be any greater than precipitation, and will usually be less because some water will run off in rivers and flow to the oceans. If potential evapotranspiration is greater than actual precipitation, then soils are extremely dry during at least a major part of the year.

Feedback Mechanisms. A mechanism that connects one aspect of a system to another. The connection can be either amplifying (positive feedback) or moderating (negative feedback). See also Climate Feedback.

Carbon Dioxide Fertilization. An expression (sometimes reduced to ‘fertilization’) used to denote increased plant growth due to a higher carbon dioxide concentration.

Fertilization. A term used to denote efforts to enhance plant growth by increased application of nitrogen-based fertilizer or increased deposition of nitrates in precipitation.

Fluorocarbons. Carbon-fluorine compounds that often contain other elements such as hydrogen, chlorine, or bromine. Common fluorocarbons include chlorofluorocarbons and related compounds (also know as ozone depleting substances), hydrofluorocarbons (HFCs), and perfluorcarbons (PFCs).

Forcing Mechanism. A process that alters the energy balance of the climate system, i.e. changes the relative balance between incoming solar radiation and outgoing infrared radiation from Earth. Such mechanisms include changes in solar irradiance, volcanic eruptions, and enhancement of the natural greenhouse effect by emission of carbon dioxide. See also Radiative Forcing.

Fossil Fuel. A general term for combustible geologic deposits of carbon in reduced (organic) form and of biological origin, including coal, oil, natural gas, oil shales, and tar sands. A major concern is that they emit carbon dioxide into the atmosphere when burnt, thus significantly contributing to the enhanced greenhouse effect.

Fossil Fuel Combustion. Burning of coal, oil (including gasoline), or natural gas. This burning, usually to generate energy, releases carbon dioxide, as well as combustion by products that can include unburned hydrocarbons, methane, and carbon monoxide. Carbon monoxide, methane, and many of the unburned hydrocarbons slowly oxidize into carbon dioxide in the atmosphere. Common sources of fossil fuel combustion include cars and electric utilities.

Framework Convention on Climate Change (). The landmark international treaty unveiled at the United Nations Conference on Environment and Development (UNCED, also known as the “Rio Summit”), in June 1992. The FCCC commits signatory countries to stabilize anthropogenic (i.e., human-induced) greenhouse gas emissions to ‘levels that would prevent dangerous anthropogenic interference with the climate system’. The FCCC also requires that all signatory parties develop and update national inventories of anthropogenic emissions of all greenhouse gases not otherwise controlled by the Montreal Protocol. Out of 155 countries that have ratified this accord, the U.S. was the first industrialized nation to do so.

General Circulation Model (GCM). A global, three-dimensional computer model of the climate system which can be used to simulate human-induced climate change. GCMs are highly complex and they represent the effects of such factors as reflective and absorptive properties of atmospheric water vapor, greenhouse gas concentrations, clouds, annual and daily solar heating, ocean temperatures and ice boundaries. The most recent GCMs include global representations of the atmosphere, oceans, and land surface.

Geosphere. The soils, sediments, and rock layers of the Earth’s crust, both continental and beneath the ocean floors.

Global Warming. An increase in the near surface temperature of the Earth. Global warming has occurred in the distant past as the result of natural influences, but the term is most often used to refer to the warming predicted to occur as a result of increased emissions of greenhouse gases. Scientists generally agree that the Earth’s surface has warmed by about 1 degree Fahrenheit in the past 140 years. The Intergovernmental Panel on Climate Change (IPCC) recently concluded that increased concentrations of greenhouse gases are causing an increase in the Earth’s surface temperature and that increased concentrations of sulfate aerosols have led to relative cooling in some regions, generally over and downwind of heavily industrialized areas. Also see Climate Change and Enhanced Greenhouse Effect.

Global Warming Potential (GWP). The index used to translate the level of emissions of various gases into a common measure in order to compare the relative radiative forcing of different gases without directly calculating the changes in atmospheric concentrations. GWPs are calculated as the ratio of the radiative forcing that would result from the emissions of one kilogram of a greenhouse gas to that from emission of one kilogram of carbon dioxide over a period of time (usually 100 years). Gases involved in complex atmospheric chemical processes have not been assigned GWPs due to complications that arise. Greenhouse gases are expressed in terms of Carbon Dioxide Equivalent. The International Panel on Climate Change (IPCC) has presented these GWPs and regularly updates them in new assessments. The chart below shows the original GWPs (assigned in 1990) and the most recent GWPs (assigned in 1996) for the most important greenhouse gases.

Greenhouse Effect. The effect produced as greenhouse gases allow incoming solar radiation to pass through the Earth’s atmosphere, but prevent most of the outgoing infra-red radiation from the surface and lower atmosphere from escaping into outer space. This process occurs naturally and has kept the Earth’s temperature about 59 degrees F warmer than it would otherwise be. Current life on Earth could not be sustained without the natural greenhouse effect.

Greenhouse Gas. Any gas that absorbs infra-red radiation in the atmosphere. Greenhouse gases include water vapor, carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), halogenated fluorocarbons (HCFCs) , ozone (O₃), perfluorinated carbons (PFCs), and hydrofluorocarbons (HFCs).

Halocarbons. Chemicals consisting of carbon, sometimes hydrogen, and either chlorine, fluorine bromine or iodine.

Halons. These man-made substances (also known as bromofluorocarbons) are chlorofluorocarbons that contain bromine. See also Chlorofluorocarbons and Related Compounds.

Hydrocarbons. Substances containing only hydrogen and carbon. Fossil fuels are made up of hydrocarbons. Some hydrocarbon compounds are major air pollutants.

Hydrofluorocarbons (HFCs). These chemicals (along with perfluorocarbons) were introduced as alternatives to ozone depleting substances in serving many industrial, commercial, and personal needs. HFCs are emitted as by-products of industrial processes and are also used in manufacturing. They do not significantly deplete the stratospheric ozone layer, but they are powerful greenhouse gases with global warming potentials ranging from 140 (HFC-152a) to 12,100 (HFC-23).

Hydrosphere. The part of the Earth composed of water including clouds, oceans, seas, ice caps, glaciers, lakes, rivers, underground water supplies, and atmospheric water vapor.

HyperText.On the web, text links move you easily from one location to another. For example, go to the site’s navigation page.

Ice Core. A cylindrical section of ice removed from a glacier or an ice sheet in order to study climate patterns of the past. By performing chemical analyses on the air trapped in the ice, scientists can estimate the percentage of carbon dioxide and other trace gases in the atmosphere at that time.

Infra-red Radiation. The heat energy that is emitted from all solids, liquids, and gases. In the context of the greenhouse issue, the term refers to the heat energy emitted by the Earth’s surface and its atmosphere. Greenhouse gases strongly absorb this radiation in the Earth’s atmosphere, and reradiate some back towards the surface, creating the greenhouse effect.

Intergovernmental Panel on Climate Change. The IPCC was established jointly by the United Nations Environment Programme and the World Meteorological Organization in 1988. The purpose of the IPCC is to assess information in the scientific and technical literature related to all significant components of the issue of climate change. The IPCC draws upon hundreds of the world’s expert scientists as authors and thousands as expert reviewers. Leading experts on climate change and environmental, social, and economic sciences from some 60 nations have helped the IPCC to prepare periodic assessments of the scientific underpinnings for understanding global climate change and its consequences. With its capacity for reporting on climate change, its consequences, and the viability of adaptation and mitigation measures, the IPCC is also looked to as the official advisory body to the world’s governments on the state of the science of the climate change issue. For example, the IPCC organized the development of internationally accepted methods for conducting national greenhouse gas emission inventories.

Joint Implementation. Agreements made between two or more nations under the auspices of the Framework Convention on Climate Change to help reduce greenhouse gas emissions.

Lifetime (Atmospheric). The lifetime of a greenhouse gas refers to the approximate amount of time it would take for the anthropogenic increment to an atmospheric pollutant concentration to return to its natural level (assuming emissions cease) as a result of either being converted to another chemical compound or being taken out of the atmosphere via a sink. This time depends on the pollutant’s sources and sinks as well as its reactivity. The lifetime of a pollutant is often considered in conjunction with the mixing of pollutants in the atmosphere; a long lifetime will allow the pollutant to mix throughout the atmosphere. Average lifetimes can vary from about a week (sulfate aerosols) to more than a century (CFCs, carbon dioxide).

Mauna Loa. A volcano on the island of Hawaii where scientists have maintained the longest continuous collection of reliable daily atmospheric records.

Meteorology. The science of weather-related phenomena.

Methane (CH₄). A hydrocarbon that is a greenhouse gas with a global warming potential most recently estimated at 24.5. Methane is produced through anaerobic (without oxygen) decomposition of waste in landfills, animal digestion, decomposition of animal wastes, production and distribution of natural gas and oil, coal production , and incomplete fossil fuel combustion. The atmospheric concentration of methane has been shown to be increasing at a rate of about 0.6% per year and the concentration of about 1.7 parts per million by volume (ppmv) is more than twice its preindustrial value. However, the rate of increase of methane in the atmosphere may be stabilizing.

Metric Ton. Common international measurement for the quantity of greenhouse gas emissions. A metric ton is equal to 2205 lbs or 1.1 short tons.

Mount Pinatubo. A volcano in the Philippine Islands that erupted in 1991. The eruption of Mount Pinatubo ejected enough particulate and sulfate aerosol matter into the atmosphere to block some of the incoming solar radiation from reaching Earth’s atmosphere. This effectively cooled the planet from 1992 to 1994, masking the warming that had been occurring for most of the 1980s and 1990s.

Nitrogen Oxides (NOx). Gases consisting of one molecule of nitrogen and varying numbers of oxygen molecules. Nitrogen oxides are produced in the emissions of vehicle exhausts and from power stations. In the atmosphere, nitrogen oxides can contribute to formation of photochemical ozone (smog), can impair visibility, and have health consequences; they are thus considered pollutants.

Nitrous Oxide (N₂O). A powerful greenhouse gas with a global warming potential of 320. Major sources of nitrous oxide include soil cultivation practices, especially the use of commercial and organic fertilizers, fossil fuel combustion, nitric acid production, and biomass burning.

Ozone (O₃). Ozone consists of three atoms of oxygen bonded together in contrast to normal atmospheric oxygen which consists of two atoms of oxygen. Ozone is an important greenhouse gas found in both the stratosphere (about 90% of the total atmospheric loading) and the troposphere (about 10%). Ozone has other effects beyond acting as a greenhouse gas. In the stratosphere, ozone provides a protective layer shielding the Earth from ultraviolet radiation and subsequent harmful health effect on humans and the environment. In the troposphere, oxygen molecules in ozone combine with other chemicals and gases (oxidization) to cause smog.

Particulates. Tiny pieces of solid or liquid matter, such as soot, dust, fumes, or mist.

Perfluorocarbons (PFCs). A group of human-made chemicals composed of carbon and fluorine only: CF4 and C2F6. These chemicals, specifically CF4 and C2F6, (along with hydrofluorocarbons) were introduced as alternatives to the ozone depleting substances. In addition, they are emitted as by-products of industrial processes and are also used in manufacturing. PFCs do not harm the stratospheric ozone layer, but they are powerful greenhouse gases: CF4 has a global warming potential (GWP) of 6,300 and C2F6 has a GWP of 12,500.

Photosynthesis. The process by which green plants use light to synthesize organic compounds from carbon dioxide and water. In the process oxygen and water are released. Increased levels of carbon dioxide can increase net photosynthesis in some plants. Plants create a very important reservoir for carbon dioxide.

Pollutant. Strictly, too much of any substance in the wrong place or at the wrong time is a pollutant. More specifically, atmospheric pollution may be defined as the presence of substances in the atmosphere, resulting from man-made activities or from natural processes that cause adverse effects to human health, property, and the environment.

Precautionary Approach. The approach promoted under the Framework Convention of Climate Change to help achieve stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous interference with the climate system.

Precession. The tendency of the Earth’s axis to wobble in space over a period of 23,000 years. The Earth’s precession is one of the factors that results in the planet receiving different amounts of solar energy over extended periods of time.

Radiation. Energy emitted in the form of electromagnetic waves. Radiation has differing characteristics depending upon the wavelength. Because the radiation from the Sun is relatively energetic, it has a short wavelength (ultra-violet, visible, and near infra-red) while energy re-radiated from the Earth’s surface and the atmosphere has a longer wavelength (infra-red radiation) because the Earth is cooler than the Sun.

Radiative Forcing. A change in the balance between incoming solar radiation and outgoing infra-red radiation. Without any radiative forcing, solar radiation coming to the Earth would continue to be approximately equal to the infra-red radiation emitted from the Earth. The addition of greenhouse gases traps and increased fraction of the infra-red radiation, reradiating it back toward the surface and creating a warming influence (i.e., positive radiative forcing because incoming solar radiation will exceed outgoing infra-red radiation).

Residence Time. The average time spent in a reservoir by an individual atom or molecule. Also, the age of a molecule when it leaves the reservoir. With respect to greenhouse gases, residence time usually refers to how long a particular molecule remains in the atmosphere.

Respiration. The process by which animals use up stored foods (by combustion with oxygen) to produce energy.

Short Ton. Common measurement for a ton in the United States. A short ton is equal to 2,000 lbs or 0.907 metric tons.

Sink. A reservoir that uptakes a pollutant from another part of its cycle. Soil and trees tend to act as natural sinks for carbon.

Solar Radiation. Energy from the Sun. Also referred to as short-wave radiation. Of importance to the climate system, solar radiation includes ultra-violet radiation, visible radiation, and infra-red radiation.

Stratosphere. The part of the atmosphere directly above the troposphere. See Atmosphere.

Sulfate Aerosol. Particulate matter that consists of compounds of sulfur formed by the interaction of sulfur dioxide and sulfur trioxide with other compounds in the atmosphere. Sulfate aerosols are injected into the atmosphere from the combustion of fossil fuels and the eruption of volcanoes like Mt. Pinatubo. Recent theory suggests that sulfate aerosols may lower the earth’s temperature by reflecting away solar radiation (negative radiative forcing). Global Climate Models which incorporate the effects of sulfate aerosols more accurately predict global temperature variations.

Sulfur Dioxide (SO2). A compound composed of one sulfur and two oxygen molecules. Sulfur dioxide emitted into the atmosphere through natural and anthropogenic processes is changed in a complex series of chemical reactions in the atmosphere to sulfate aerosols. These aerosols result in negative radiative forcing (i.e., tending to cool the Earth’s surface).

Sulfur Hexafluoride (SF6). A very powerful greenhouse gas used primarily in electrical transmission and distribution systems. SF6 has a global warming potential of 24,900.

Trace Gas. Any one of the less common gases found in the Earth’s atmosphere. Nitrogen, oxygen, and argon make up more than 99 percent of the Earth’s atmosphere. Other gases, such as carbon dioxide, water vapor, methane, oxides of nitrogen, ozone, and ammonia, are considered trace gases. Although relatively unimportant in terms of their absolute volume, they have significant effects on the Earth’s weather and climate.

Troposphere. The lowest layer of the atmosphere. The troposphere extends from the Earth’s surface up to about 10-15 km. See also Atmosphere.

Tropospheric Ozone (O₃). Ozone that is located in the troposphere and plays a significant role in the greenhouse gas effect and urban smog. See Ozone for more details.

Tropospheric Ozone Precursor. Gases that influence the rate at which ozone is created and destroyed in the atmosphere. Such gases include: carbon monoxide (CO), nitrogen oxides (NOx), and nonmethane volatile organic compounds (NMVOCs).

Water Vapor. The most abundant greenhouse gas, it is the water present in the atmosphere in gaseous form. Water vapor is an important part of the natural greenhouse effect. While humans are not significantly increasing its concentration, it contributes to the enhanced greenhouse effect because the warming influence of greenhouse gases leads to a positive water vapor feedback. In addition to its role as a natural greenhouse gas, water vapor plays an important role in regulating the temperature of the planet because clouds form when excess water vapor in the atmosphere condenses to form ice and water droplets and precipitation.

Weather. Weather is the specific condition of the atmosphere at a particular place and time. It is measured in terms of such things as wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. In most places, weather can change from hour-to-hour, day-to-day, and season-to-season. Climate is the average of weather over time and space. A simple way of remembering the difference is that ‘climate’ is what you expect (e.g., cold winters) and ‘weather’ is what you get (e.g., a blizzard).

The paper published by Frank Wentz and Matthias Schabel in Nature this week (August 14, 1998) is bound to generate controversy about the satellite measurements of global tropospheric temperatures. These measurements, for the period since 1979, have been made with the TIROS-N satellite Microwave Sounding Units (MSUs) by myself and Dr. John Christy (The University of Alabama in Huntsville). We are grateful to Wentz and Schabel for discovering the first convincing evidence for needed corrections to our satellite-based global temperatures.

However, we believe that there are a few important points that should be considered when reporting on this paper.

1) The spurious cooling in the satellite record due to the orbital decay (”downward drift”) effect was only estimated by Wentz and Schabel as an average adjustment to our processed satellite data. The effect, which will have different values for the eight different satellites in the record, should instead be removed one satellite at a time before the satellites in the record are intercalibrated. We (John Christy and Roy Spencer) have performed this adjustment, with the results given below.

2) The effect reported by Mr. Wentz had been partly offset by an east-west drift in the satellites’ orbits. The valuable discovery of the downward drift effect by Wentz and Schabel allowed us to separately quantify two consequences of the east-west drift (MSU instrument temperature change, and observation time-of-day change). We have now performed these adjustments as well (below).

3) The global decadal temperature trends, for the period 1979-1997, from the various satellite, weather balloon, and surface temperature measurements are as follows, in order of increasing temperature trend:

DEEP LAYER MEASUREMENTS


Weather balloon trend (Angell/NOAA)

-0.07 deg. C/decade

Unadjusted satellite trend:

-0.04 deg. C/decade


Weather balloon trend (Parker, UK Met Office):

-0.02 deg. C/decade


Our Adjusted Satellite Trend:

-0.01 deg.  C/decade


Wentz-estimated adjusted satellite trend:

+0.08 deg. C/decade


SURFACE MEASUREMENTS


Sea surface and land surface temperatures (U.K. Met Office):

+0.15 deg. C/decade

It can be seen that the adjustment by Wentz and Schabel does not agree with our (more complete) adjustments, or to the weather balloon data. Instead, their adjustment comes closer to the surface thermometer measurements, and herein lies a temptation to jump to conclusions. 

4) The adjusted satellite trends are still not near the expected value of global warming predicted by computer climate models. The Intergovernmental Panel on Climate Change’s (IPCC) 1995 estimate of average global warming at the surface until the year 2100 is +0.18 deg. C/decade.

Climate models suggest that the deep layer measured by the satellite and weather balloons should be warming about 30% faster than the surface (+0.23 deg. C/decade). None of the satellite or weather balloon estimates are near this value.

5) 1998 UPDATE: The last six months of our adjusted satellite record (February through July 1998) were the warmest in the 20 year record. The updated trend is now +0.04 deg. C/decade (which is still only 1/6th of the IPCC-expected warming rate). The current demise of El Nino, and the possibility of a La Nina forming, will likely cause significant cooling in the coming months.

Text references for this study

Executive Summary

Understanding the causes for changes in the weather day to day and year to year can be difficult because the complex systems underlying weather and climate change are not completely understood.

Recent articles in the press have reported that our weather is becoming more and more extreme and more destructive. Hurricane Andrew, devastating floods in California and the Midwest and the brutal winter storms that struck the Northeast last year are cited as the most recent signs that extreme weather events are becoming more intense and more frequent. Some people suggest that the planet is becoming warmer, largely as a result of the increased use of energy and the resulting increase in carbon dioxide and other “greenhouse” gases, and that this warming is causing weather to become more extreme.

But what are the facts? Is our weather becoming more hostile? To find out, the Global Climate Coalition asked Accu-Weather, Inc., to investigate historical weather records to determine if severe weather events are more frequent or more intense today than in the past and to uncover any scientific basis for linking “global warming” to our changing weather.

Accu-Weather examined relevant historical land, water and satellite weather data, conducted numerous personal interviews with scientists active in the field, reviewed pertinent literature on the subject and analyzed global weather data published by various organizations. Accu-Weather concludes that:

• No convincing observational evidence has been found to show that hurricanes, violent tornadoes and other extreme events are more common now than they were 50 or 100 years ago. The greater attention now paid to sever weather events may simply reflect three non-weather related facts: (1) more people live in areas that were once sparsely populated or even uninhabited; (2) local media are now able to quickly report severe weather events that are occurring, or have just occurred, in distant parts of the globe; and (3) more sophisticated weather monitoring systems and a more widely distributed population mean that extreme events in remote areas are more likely to be detected.

• The number of deaths in the United States caused by extreme weather disasters declined during the latter part of the century, but the values of property damage increased. This reflects both the improvements made in systems for detecting and providing early warning of danger, and the fact that more people are populating areas where severe weather is likely to occur.

• Average global temperatures have increased slightly within the past 100 years, but this increase falls within the limits of natural climate variability and does not necessarily signal that greenhouse gases are causing global warming. Much of the temperature increase occurred before 1940, while the majority of greenhouse emissions occurred well after 1940.

Weather Changes - The Variability of the Terrestrial Climate

Does climate change? Yes.

The Earth’s climate has changed drastically, and often over geological time. All of the reasons for these changes are not completely understood, but we know that climate change predates human history. Many theories have been advanced to explain these climate changes, including theories about changes in the sun’s energy output, the Earth’s orbit, volcanism, meteorite showers and most recently “the greenhouse effect.”

Significant long-term changes in the Earth’s climate have occurred in the past and, no doubt, will occur again. This has led some people to ask when the next significant change in climate will occur, and whether human activity has inadvertently accelerated the onset of climate change. While it is impossible to answer these questions unequivocally, studies of observational data and an understanding of theoretical issues of climate do offer some insight. Put briefly, climate changes for many reasons. While climate models project that anthropogenic greenhouse gas emissions may be responsible for recent and future global climate changes, there is no convincing observational evidence to support these projections, despite observed increases in greenhouse gas and aerosol concentrations during the last 100 years.

There continues to be considerable scientific uncertainty on a.) whether or when global warming will occur and b.) what influence such hypothesized warming would have on severe weather intensity and frequency.

Some people outside the scientific community predict apocalyptic climate changes within the next few decades. Others expect the climatological “status quo” to prevail well into the future. However, we have not found convincing evidence to support the hypothesis that extreme weather events, presumed to be associated with global warming, are already increasing.

There is no question that the Earth has been subjected to many climatological extremes over geological time, measured in thousands, even millions, of years. Numerous ice ages have come and gone, with warm and even very warm periods intertwined. Although the reasons for such changes are not completely understood, significant influences are attributed to changes in the Earth’s orbit around the sun, to changes in the energy output of the sun, volcanism and to meteorite impacts.

As noted, the climactic changes over the past million years or so have been stroking, with cycles of major glaciation and deglaciation. These temperature cycles, determined from the studies of oxygen isotopes in ice cores, show significant peaks in the glaciation intervals of one hundred thousand, forty-three thousand, twenty-four thousand, and nineteen thousand years (Imbrie & Imbrie, 1979). The generally accepted hypothesis for this quasi-periodic behavior is that orbital variations of the Earth have been the major factor that has “forced” long-term climate changes. This is referred to as the Milankovitch mechanism. These orbital variations consist of three factors: changes in the obliquity (tilt) of the Earth’s rotation axis, the precession of the equinoxes along the Earth’s elliptic orbit, and changes in eccentricity of the orbit. These variations are schematically illustrated in Extra-terrestrial variables however, are not at the heart of today’s argument about the so-called “greenhouse effect.” In Figure 2 we illustrate in graphic form the simplified model of the greenhouse effect. Simplified models such as this are often relied upon in the popular press when explaining the importance of greenhouse gas emissions. The fundamental concept is that the atmosphere is transparent to visible radiation from the sun,(A significant fraction of solar radiation is relected back out to space by clouds and the surface of the Earth) which heats the Earth’s surface. The Earth’s surface in turn heats up the atmosphere by radiating energy in the form of infrared (IR) radiation back out toward space. The IR radiation increases as the average temperature of the Earth’s surface rises. The temperature adjusts until a balance is achieved. If the atmosphere were also transparent to IR radiation, then the IR radiation produced by an average surface temperature of about -18 degrees Celsius (C) would balance the incoming solar radiation, i.e., the temperature of the Earth would be -18 degrees C based on the present rate of solar energy and the distance of the earth from the sun. However, the atmosphere is not transparent to the infrared, because of the radiative absorbing properties of such “greenhouse gases” as water vapor, carbon dioxide and methane. The energy absorbed by the greenhouse gases is partially radiated back to the Earth’s surface, increasing temperatures in the lower atmosphere (and decreasing temperatures at higher levels). This warming is called the “greenhouse effect,” for it makes the Earth’s average surface temperature +15 degrees C rather than -18 degrees C.

The main absorbers of IR in the atmosphere are water vapor and clouds. We note here that since water in its various forms is the principal absorber of IR, even if all the other greenhouse gases were to disappear, we would still be left with a significant fraction of the current greenhouse effect. Nevertheless, it is presumed that increases in carbon dioxide and other minor greenhouse gases can lead to significant increases in temperature. Atmospheric concentrations of some of the other greenhouse gases have increased in the last century. A widely held contention is that these increases will continue well into the future, as they have for the past century, thereby enhancing the greenhouse effect.

It should be emphasized that such “popular press” descriptions of the greenhouse effect are overly simplistic and have a tendency to mislead non-scientists in understanding the physics involved in climate change projections. Indeed, calculations of the incoming versus outgoing radiation energy flux show that the tropics receive more heat from the sun than they radiate back out to space. Conversely, the polar regions radiate more heat back than they receive from the sun. The simplistic model shown in Figure 2 shows the radiation process only, whereas, in fact, heat is also transported vertically and horizontally by the wind and by ocean currents to maintain thermal balance. The importance of this concept has been treated in detail by Piexoto and Oort (1992), who show that without a horizontal transport of heat from the equatorial regions toward the poles, the tropics would become excessively hot and the polar regions uninhabitably cold.

Much of the surface of the Earth, especially the oceans, also cools by evaporation. Most of the evaporative moisture ends up in convective clouds (clouds with strong upward and downward motion of the air), which carry the air and its contents upward, where moisture condenses into rain and snow. Just as evaporation takes hear away from the environment (cooling), the condensation of water vapor releases heat. The atmosphere receives heat from condensation of water vapor. The atmosphere must balance the heat deposited by convection from the surface with cooling by thermal radiation. Water vapor at the surface and condensation is a major heat transfer mechanism without which the earth’s surface would become unbearably hot (Lindzen, 1994a).

In addition to the convection and greenhouse effect, other internal climatic forcing functions can play an important role in non-geological climate change. For example, the interaction between the ocean and atmosphere is known to produce significant short-term changes in the climate over large regions of the globe. The quasi-periodic appearance of El Nio Southern Oscillation (ENSO)(ENSO events, also known as El Nino, are naturally occurring phenomena that occurred before and have continued to occur after the significant increase in greenhouse gases.) is a prime example of this, and the short-term impact of El Nio on global weather has been well documented for several decades. Similarly, isolated volcanic activity also appears to influence the global climate for relatively short periods of time. The recent eruption of Mount Pinatubo illustrates the short-term cooling effect of volcanic eruptions on global temperatures. While current climate models have equations which attempt to mimic the important physical processes involved in the greenhouse effect (convection, evaporation, ENSO, volcanic eruptions, etc.), popular press greenhouse effect descriptions generally ignore these important details.

Climate Change Over the Past Century (The Observations)

Do observed data indicate significant global temperature changes?

No. Global air temperatures as measured by land-based weather stations show an increase of about 0.45 degrees C over the past century. This may be no more than normal climatic variation. However, several biases in the data may be responsible for some of this increase. Moreover, much of the observed temperature increase during the past century occurred before the rise in greenhouse gases.

Reliable global weather observations extend back to the end of the 19th century. This information is essentially confined to observations of the temperature of the air near the surface of the Earth. Detailed observations of the distribution of water in its various forms, the wind and other elements both at the surface and higher levels of the atmosphere are available only for the past half century. Consequently, searches for signals of climate change over the past one hundred years have been restricted essentially to the observations of temperatures at specific stations around the world, the greatest density of which are on land, in populated areas such as North America and Europe. Before we present the observations involved in the climatic change to date, it is important to consider the general problem of “bias” in such data. The problem with generating “unbiased” air temperature and sea surface temperatures is described in detail in “Climatic Change - The IPCC Scientific Assessment 1992″ and numerous other sources (Jones, 1990a). We summarize the sources of bias below.

Biases In Air Temperature Data

The IPCC Scientific Assessment provides an important discussion of problems associated with the surface air temperature record. It states that “a number of problems may have affected the record” (IPCC ‘92, pg. 207). They list these problems as:

1. spatial coverage of the data is incomplete and varies greatly;

2. changes have occurred in observing schedules and practices;

3. changes have occurred in the exposures of thermometers;

4. stations have changed their locations;

5. changes in the environment, especially urbanization, have taken place around many stations.

Much effort is expended by the scientific community in attempting to remove such effects from the data. There are several potential sources of bias:

a.) Uniform Standards “There is no international standard for the calculation of mean daily temperature. Few countries have even maintained the same practice over the past century. These changes introduce bias into the record. Many of these biases can be significant. The IPCC states that some of these biases have been corrected in existing global records, “but some have not.” They also state that these biases can be significant. (IPCC 1992, pg. 207-208)

b.) Exposure Effects “Substantial systematic changes in the exposure of thermometers have occurred. Because thermometers can be affected by the direct rays of the sun, reflected solar radiation, extraneous heat sources and precipitation, there has been a continuous effort to improve their exposures over the last 150 years. Additional biases must accompany these changes in the thermometric record. Since many of the changes in exposure took place during the nineteenth and early twentieth centuries, that part of the record is most likely to be affected…The effects of exposure changes vary regionally (by country) and seasonally. Thus, tropical temperatures prior to the late 1920’s appear to be too high because of the placement of thermometers in cages situated in open sheds. There is also evidence that for the mid-latitudes prior to about 1880, summer temperatures may be too high and winter temperatures too low due to the use of poorly screened thermometers. These effects have not yet been accounted for in existing analyses.” (IPCC 1992, pg. 208)

c.) Observation Schedules “Artificial changes of temperature of either sign may exist in other parts of the world due to changes in observation time but have not been investigated.” (IPCC 1992, pg. 208)

d.) Correction Procedures “Changes in station environment can seriously affect temperature records…When reallocations occur in a random manner, they do not have a serious impact on hemispheric or global temperature anomalies, though they impair our ability to develop information about much smaller scale temperature anomalies. A bias on a large scale can emerge when the character of the change is not random. An example is the systematic relocation of some observing stations from inside cities in many countries to more rural airport locations that occurred several decades ago. There are several possible correction procedures that have been, or could be, applied…All depend on denser networks of stations than are usually available except in USA, Europe, the Western Soviet Union and a few other areas.” (IPCC 1992, pg. 209)

e,) Urban Bias “Of the above problems, increasing urbanization around fixed stations is the most serious source of systemic error for hemispheric land temperature time series that has so far been identified.” Researchers have found that urbanization can cause a bias of 0.1 degree C, even when urban areas have populations as low as 10,000. Some new rural airport locations may have suffered recently from increasing urbanization. (IPCC 1992, pg. 209)

f.) Agricultural Heat Islands Some “heat island” effects, especially during the growing season, may also have been introduced in rural agricultural areas during the past half-century. The increase in irrigation systems in many parts of the world has allowed the area extent of crops grown in “desert” areas to expand. Expansion is accompanied by an increase in local water vapor concentrations and evaporation. Wetting the ground also raises nighttime temperatures by increasing soil conductivity and raising the dew point, thus limiting the amount the temperature can drop.

g.) Sparse Data in the Southern Hemisphere Southern hemisphere ocean temperatures have always been poorly measured. Differences in existing historical data sets exist because of differences in assumptions about the mix of wooden versus canvas buckets used during the nineteenth century. (IPCC 1992, pages 210-211) An absence of data in the polar regions of the Southern Hemisphere prior to the middle of the twentieth century also introduces uncertainty into the air temperature record.

Biases in Sea Surface Temperature Data

Concerns about sparse data are even more applicable to sea surface temperatures. Moreover,

1. The manner in which water temperatures are sampled has changed considerably over the past century. The types of buckets used in making measurements were changed, as were the depths to which the bucket is lowered into the ocean. For data collected prior to 1942, this situation has necessitated the development of varying corrections. Despite these corrections, some differences in historical sea surface temperatures remain in different data sets. Since 1942, no corrections have been applied to sea surface temperature data. (IPCC 1992, pages 209-211)

2.) There are many uncertainties in the interpretation of early marine temperature records. Some researchers have used a mixture of weather-ship air temperature data and selected land air temperature data to calculate corrections. There is still concern that these corrections may be influenced by biases in the land data, including warm biases arising from the use of tropical open sheds earlier this century. (IPCC 1992, pg. 212)

Given all the uncertainties in the measurements, climatologists have done their best to reconstruct global air and sea surface temperatures; e.g. “Trends ‘93″ (Oak Ridge National Laboratory 1993). Figure 3 presents average annual global air temperature anomalies (Oak Ridge National Laboratory 1993) from 1880 to 1993. Figure 4 presents hemispheric data for the sea surface temperature anomalies. When the two time series are combined in Figure 5 (from IPCC 1993) the temperature increase over the record is approximately 0.5 degrees C. The most significant increase in air temperature prior to the 1970s occurred from about 1916 or 1917 to the mid-1940s. That, in turn, was followed by some cooling in the 1950s through the 1960s and some warming in recent decades.

Some climatologists have argued that the apparent rise in air temperature from the mid 1970s (shown in Figure 3) through the 1980s is proof that human-induced global warming has begun. Recent satellite observations show different global temperature trends than surface air temperature data. Unlike surface thermometers, satellites can: (a) measure the integrated air temperature over several thousand feet in the vertical, (b) measure temperatures at various levels in the atmosphere, and (c) provide nearly complete Earth coverage in as little as a day (Spencer and Christy, 1990). Experiments comparing the satellite temperatures to those measured by radiosondes have supported the accuracy of the former.

Figure 6, from Oak Ridge National Laboratory (1993) displays the lower tropospheric temperature trends (i.e., below about 10,000 feet) from 1979 through 1993, as obtained from satellite measurements. It is clear that over the past one-and-a-half decades, lower tropospheric temperatures obtained from satellites have not shown any significant increase. This is in contrast to the Wilson/Hansen and John/Wigley data (Figure 3), which show an increase. In out opinion, hemispheric satellite temperature data must be considered more representative of global atmospheric temperatures than surface temperature data, which have non-homogeneous spatial distributions and are representative of a very thin layer of air at the surface. In addition, if significant changes in lower level temperatures were occurring, corresponding changes should be reflected in the lower troposphere and should show up in the satellite data. Therefore, since no statistical trends are detectable in the satellite data, whatever is happening at the surface must have a minor effect on overall global atmospheric temperatures.

Is Today’s Weather More Extreme?

Are weather variations much more extreme today than they were 50 to 100 years ago?

No. Although some people have argued that hurricanes are becoming stronger and more frequent, that tornadoes have increased in number and that droughts and floods are becoming more common, recent work by scientists worldwide disputes this hypothesis. In fact, observational data show that the frequency of both hurricanes and violent tornadoes have not increased in recent decades. Sound theoretical arguments have been advanced that indicate even if global warming does occur, the frequency and aerial extent of hurricanes are not likely to increase.

Ever since the first simple climate models were used to make predictions of global warming a dozen or so years ago, there has been much concern in the media. The media promoted many erroneous concepts about climate change. For example, “Global Warming Unchecked” (1993), Bernard describes in detail how global warming will cause catastrophic weather changes in the United States from the West through the Great Plains, Midwest and into the East and the South. Others have predicted an even more significant effect of global warming on such often calamitous meteorological phenomena as tropical storms. This is typified by Friedman (1989) who, using theoretical arguments advanced by Emmanuel (1987-88), hypothesizes that since global warming means higher sea surface temperature, that in turn will:

A. Lengthen the tropical storm and hurricane season;

B. Extend the area over which tropical storms and hurricanes can form;

C. Cause tropical storms and hurricanes to be more intense; and

D. Cause more tropical storms and hurricanes to strike the United States.

Other writers in the popular press (e.g., Flavin, 1994) have expressed ideas that are more extreme. Some claim that global warming has already affected the world, not only seen in the (alleged) increase in tropical storm and hurricane intensity and frequency, but also in the number of floods, intense middle latitude storms and droughts over the recent past. They cite the many media reports of severe weather events from all corners of the world as evidence that global warming has already occurred.

The popular press often ignores important statistical principles when writing about the climate. For example, statements about the “average” rainfall or “average” temperature do not contain complete information about the behavior of that meteorological variable. The average value, or as it is sometimes called the mean,(The terms “normal” and “average” are used interchangeably here.) of any variable is composed of variations about that average, or, in statistical jargon, the variance(also expressed as the “standard deviation” which is the square root of the variance). Some averages are composed of large (or high) variances of the measured quantity while others may have small variations. Indeed, the average rainfall (or temperature) may be the same at two locations but the variations about that average can be completely different. In Figure 7, we show a hypothetical times series of the variation of a weather element at two different locations over the same time interval. Both have the same average, but the variations around that average are significantly different.

There is another fundamentally important concept concerning the application of statistical techniques in scientific research that needs to be noted. This concept states that great care should be exercised in assuming that there is a cause and effect relationship between two events, even if the two events occur simultaneously or in phase with one another. One must be very careful in using statistical relationships to establish or even postulate physical processes that may be causing correlations between two events, or using such correlations for predictive purposes. For example, every human being who has lived for more than a few days has either died or is on their way to death, and all of them, at one time or another, drank water. Therefore, using a causal “cause and effect” reasoning, it follows that drinking water results in death. In fact, we know that the opposite is true, that without water death is predictable in a short period of time. This illustrates the danger of using pure statistical relationships to infer the physical reasons for events occurring.

Friedman and others have assumed that sea surface temperature greater than or equal to 26 degrees C is the only condition necessary for the formation of tropical storms. In addition, it was assumed that both the real extent and the length of time sea surface temperature equals or exceeds 26 degrees C would also increase as global temperatures increase. This simplistic reasoning has led to the conclusion that the tropical storm season would lengthen and the area of tropical storm formation would expand. In other words, there would be more tropical storms over longer periods of time and over larger areas. Assumptions have also been made(The assumption was based on theoretical arguments involving thermodynamic energy transfer processes.) that as tropical storms and hurricanes mover over higher sea surface temperatures, they would increase in intensity, ergo, there would be more intense tropical storms in the future as global warming takes place.

Recently, Lighthill and Holland, et al. (1994), have shown that these simplistic arguments and assumptions are not true. Specifically, the referenced article summarizes studies of tropical storms and hurricanes conducted by the nine authors over the last decade. Based on observational studies of tropical storms in the Northern Hemisphere, the authors concluded that the intensity of tropical storms is not directly related to sea surface temperature. In fact, they found no correlation between the intensification (or maximum intensity) of tropical storms and sea surface temperature. Moreover, the Lighthill and Holland study also shows there is no correlation between the Northern Hemispheric air temperature anomalies over the past several dozens of years and the maximum intensities reached by tropical storms. (See Figure 8.)

Rather, as Lighthill and Holland et al. point out, six conditions are necessary before a tropical storm forms and intensifies. A minimum sea surface temperature of 26 degrees C is only one of those conditions. The others are:

(1) The distance from the equator needs to be at least five degrees of latitude to bring into play what meteorologists call the Coriolis Effect produced by the Earth’s rotation. This effect generates cyclonic spiraling, or the counter-clockwise rotation of storm systems in the Northern Hemisphere and clockwise rotation in the Southern.

(2) The gradient of temperature decrease with height must be large enough so that the air that has become saturated with water vapor near the so-called “eye-wall” of the storm will be able to continue to rise as it moves up into the atmosphere.

(3) Low values of the vertical wind shear(The change in direction or speed, or both, of the horizontal wind with height near the center of the storm) are needed to avoid excessive departure from a vertically symmetric vortical structure, considered necessary to maintain or allow tropical storm evolution.

(4) Relative humidity has to be high enough in the middle troposphere to avoid drying effects of the air that becomes entrained into the eye-wall of the storm system.

(5) Finally, there must be the prior existence at low altitudes of a rather substantial amount of cyclonic vorticity, which in more common language, means there needs to be a pre-existing tendency for a counterclockwise spinning component(In the Norhtern Hemisphere) of the atmosphere to be present close to the surface of the ocean.

These conditions, derived from extensive observational records, emphasize that much more than just a sufficiently high sea surface temperature is needed for tropical storm formation and intensification. Condition 3, as listed above, (low vertical wind shear) is particularly important, and this is independent of sea surface temperature.

Consition 1 imposes a lower limit on those latitudes north and south of the equator where tropical storms can form. This upper limit, between 15 and 20 degrees from the equator, is set by the lower latitudinal boundary of a region in the atmosphere where downward motion of the air generates the “trade inversion.” This region is part of a large scale circulation that meteorologists call a Hadley Cell. Thius downward motion tends to dampen any upward motion induced by heating or horizontal forcing and is therefore unfavorable for tropical storm development.

Hadley Cells are determined by the orbit and shape of the Earth and the adage that “what goes up must come down.” (See Figure 9). The Hadley Cell’s ascending branch, air rising from hot regions near the equator, is balanced by subsidence of the air in its descending branch, stretching poleward an average of 15 to 20 degrees of latitude. This branch of the Hadrey Cell is associated with a slow, downward motion of the atmosphere. Accordingly, unlike the fast ascent of moist air in the tropical storm’s eye-wall, the subsiding air in this region of the Hadley Cell loses, by radiation, much of the heat if gains by compression. Thus the gradient of temperature drop with height becomes far too low for condition 2 to be satisfied in this region.

This and other evidence presented by Lighthill and Holland et al. casts serious doubts on the validity of the hypothesis that any future increases of sea surface temperature must widen the band of latitudes where tropical storms can intensify. Because subsidence, that is the downward motion in the descending branch of the Haldey Cell, prevents condition 2 and condition 4 from being reached there is little likelihood that the area of tropical storm formation will widen significantly. In short, all six conditions for tropical storm formation must be satisfied in order for there to be more frequent or more intense tropical storms. In addition, global warming would raise the temperature of the sea surface above 26 degrees C mainly in the regions where conditions 2 and 4 cannot be satisfied. Consequently, even if global warming were to occur, it appears that there would be very little, if any, effect on tropical storm development.

In summary, Lighthill and Holland et al. present credible reasons to reject the hypothesis that more intense or more frequent tropical storms would occur, even if surface sea temperatures significantly increased in response to global warming.

As for the frequency of other extreme weather events, the evidence we have examined does not support the extremists’ claim that, recently, the number of unusual weather events has increased. Once again we refer back to our discussion of averages versus variances and note that “climate” is defined as the average, over time, of the variations of meteorological elements that we call “weather.” In most instances, the variance of meteorological elements such as temperature and precipitation in the temperate and polar regions is usually high. Consequently, extreme departures from “average” weather patterns are to be expected in these areas.

However, many people today believe the weather is more extreme than it used to be. In large part this may be due to the media’s high-speed electronic ability to rapidly report worldwide events, including the weather. For example, we know almost instantaneously when a tropical cyclone devastates Bangladesh, or that a drought is occurring in Australia. In the past, few people in the United States were aware of these events. The same phenomenon is of course occurring worldwide with the recent explosion of cable and satellite television.

The observational evidence, however, suggests that weather extremes are not significantly different today than they were in the past. Hurricane(Tropical storms that reached hurricane force, sustained winds greater than or equal to 74 mph) data are a prime example. Figure 10 presents data on the frequency of typhoons and hurricanes in the northeast and northwest Pacific Ocean during the past few decades (Lighthill and Holland et al. 1994). The data show that typhoons and hurricanes have not increased in number or intensity during the past few decades. Figure 11 (National Weather Service, 1992) summarizes the number of tropical storms that became hurricanes in the Atlantic Ocean from 1880 through 1992. It is apparent from these data that the number of North Atlantic hurricanes has not increased significantly in recent years.

Moreover, when one considers that satellite observations have been very effective in locating and tracking storms for the past couple of decades, it is possible that the number of hurricanes in the Northern Hemisphere actually may have decreased in recent years. Some storms that we detect now probably would have gone unnoticed 50 to 100 years ago.

Questions have also been raised as to the possibility that severe, localized storms, such as tornadoes, are on the increase. Figure 12 presents data by Ostby (1993) on the frequency of tornadoes observed in the 48 contiguous states from 1953 to 1993. The top curve is the sum of weak, strong and violent tornadoes. Weak tornadoes are those with peak winds less than 112 mph, while strong tornadoes have peak winds from 113 to 206 mph. Violent tornadoes contain winds from 207-318 mph. As the reader can easily see, the increase in the total number of tornadoes is due to an increase in the number of weak, but not strong or violent, tornadoes over the past 40 years. Ostby attributes the increase in reports of weak tornadoes to several factors including: greater population and public awareness of tornadoes in tornado-prone areas, storm-chasing, and the advent of the video camera. Expanding population and public awareness are especially relevant because tornadoes are small storms and in days of more thinly dispersed population, many weak tornadoes undoubtedly went unreported. As the data show there is no evidence of an increase in strong or violent tornadoes over the 40-year sample in the 48 contiguous states. In fact, there appears to be an overall downward trend of such storms during the past 20 years.

Although we have not found any evidence of a significant increase in the frequency of tropical storms, hurricanes or tornadoes in recent years, a recent study (Karl and Baker, 1995), has shown that the average temperature and precipitation have increased over the past century in the contiguous United States. Once again, the question can be raised that if the average increases, does this mean that extremes will also increase? The answer is not simple, and it refers back to our previous discussion about the variation of a meteorological variable about its average. As shown in Figure 7,, knowledge of the average does not necessarily give us information about the variations from the average. For example, the recent heavy rainfall in January 1995 in California might be used as an example of an extreme event accompanying increased average rainfall. See Table I and Figure 13 for rainfall records in Los Angeles (Civic Center) from 1878 through 1993. Table I shows the monthly record rainfall in Los Angeles over the past 115 years. As one can see, five monthly record-high rainfall amounts occurred before this century. The heaviest annual total rainfall occurred in 1884. Figure 13 presents the number of months, over 10-year intervals, with total monthly rainfall greater than 7.00 inches. The greatest number of months with rainfall greater than 7.00 inches occurred from1930-1939. The total for the five previous decades is 20, while the total number of months with rainfall greater than 7.00 inches over the most recent five decades is 19.

Thus there is no evidence from the Los Angeles records that rainfall extremes have occurred more frequently in recent times. We note that the Los Angeles data are not representative of the entire country, but the data do not support the argument that an increase in average rainfall equates to an increase in extreme events.

To further substantiate the thesis that a large departure from the average of a meteorological element does not necessarily mean the departure is “extreme” we present Table II where the Monthly and Annual Standard Deviations of Rainfall as a percentage of the average for various sections of the 48 contiguous United States is displayed for the period from 1900 to 1993. The statistics were computed by Bronson Gardner, (personal communication, 1995) from the U.S. Historical Climatological Network data (Karl et al., 1994).

As an example of how the table can be interpreted, in the Coastal Section of the Northeast (blocked) in March, 66% of the time the monthly rainfall will be within 34.3% of the average. Whereas in the South Pacific Coastal area (blocked) of the USA in June, 66% of the time the rainfall will be within 192.2% of the average. In the latter example, the average rainfall is slight, well under one inch, thus even a small amount of rainfall could be considered an extreme. As for the former case, the average is much higher, being on the order of 4 inches, consequently a very large amount of rainfall is necessary before it can be considered an extreme.

As previously noted, Karl and Baker, 1995 also show that there has been an increase in the average temperature in the contiguous United States. We have examined a sample of record-high temperatures during the past century for a geographical cross-section of the United States east of the Rocky Mountains. These locations were selected because their data would not be greatly biased by the urban heat island effect and because they represented different climate zones. In Figures 14a through 14c we present the number of daily high temperature records set in 5 year periods at Des Moines, Iowa, Augusta, Georgia and State College, Pennsylvania. Note that if a record-high temperature for a specific calendar date matches one on the same date of any previous year it is assigned to the most recent date. Thus, there is a built-in bias, albeit probably small, toward the appearance of more record highs in recent years. Nevertheless, one can see that many daily high temperature records were set at the four locations prior to the last decade or two. There is no consistent evidence in Figures 14a through 14c that record-breaking high temperatures have been restricted to or are occurring more frequently in recent years, at the locations studied.

Changes In Greenhouse Gas Emissions

Greenhouse gases in the atmosphere have increased. As a result, has significant global warming been detected?

No. The amounts of carbon dioxide, methane and other greenhouse gases have increased in the atmosphere in the last century. A rapid increase began in the 1950s. But the observed global temperature rise from 1916 to the 1940s is not in phase with this increase.

The major greenhouse gas in the terrestrial atmosphere is water vapor. Minor greenhouse gases that are produced either naturally or by human activity include carbon dioxide, methane, chlorofluorocarbons and nitrous oxide. Of these minor gases, the most important, by far, is carbon dioxide. However, even carbon dioxide absorbs only about 5 percent of the total amount of infrared radiation from the Earth, compared to 90 to 95 percent absorbed by water in the form of clouds and/or water vapor.

There is no question that the atmospheric concentrations of carbon dioxide and the other minor greenhouse gases have increased. Figure 15, presents the history of carbon dioxide, methane and nitrous oxide concentrations from 1750 to the beginning of this decade. Observations prior to 1958 were obtained from ice cores, but since then they are based on direct atmospheric sampling.

How have these trends toward increased emissions and atmospheric concentration of greenhouse gases been interpreted? Simplistic models of the greenhouse effect (see Figure 2) “predict” that rapid increases in carbon dioxide in the atmosphere during the past century should have significantly increased global temperatures, especially in recent years. Yet there is no consistent, obvious signal announcing the presence of substantial global warming in any of the data that the authors examined. There is a general consensus in the scientific community that there has been a gradual increase of about 0.45 degrees Celsius, plus or minus 0.15 degrees Celsius, in the average global temperature since the late 1800s. However, that increase is within the realm of natural variability. In fact, the 1992 IPCC Supplemental Report states that the “global mean surface air temperature has increased by 0.3 to 0.6 degrees Celsius over the last 100 years…is…of the same magnitude as natural climate variability.” It is important to note that a significant fraction of the observed air temperature increase in the last hundred years occurred between 1916 and the mid-1940s, before the rapid increase in carbon dioxide emissions. Since much of the observed global warming occurred before the steep rise in greenhouse has concentrations, the warming must have been caused by other factors.

Summary and Conclusions

What does the future hold?

No one knows for certain. However, one can expect hurricanes, tornadoes, floods and droughts to be similar in intensity and frequency to those that have occurred in the past. Also, because world population is growing and people are building in previously uninhabited areas, world governments, weather sensitive industries and others need to prepare to handle extreme weather events. Catastrophic extreme weather events will continue regardless of whether or not climate change occurs. Additionally, research is needed to improve climate models as well as our understanding of the factors that influence climate. Observational studies also are needed in order to better document the Earth’s variable climate.

Even if the Earth has warmed slightly during recent decades a modest increase in the Earth’s temperature has not caused more tropical storms, hurricanes or tornadoes. And although Hurricanes Andrew and Hugo caused extensive property damage, these storms were no stronger than past storms. In fact, the hurricane that struck the Florida Keys in 1935 was more intense than Andrew or Hugo. However, it struck a sparsely populated area and so caused considerably less property damage and claimed fewer lives than either Andrew or Hugo.

Science and technology cannot prevent all loss of life and property from severe storms, but society can track its vulnerability, forecast extreme events, communicate warnings, improve land use and design safer structures. A number of organizations are doing just that including the National Hurricane Center in Coral Gables, Florida; the Natural Hazards Research and Applications Center at the University of Colorado; The World Meteorological Organization (WMO) in Geneva, Switzerland, and the United Nations Technical Committee in New York City. Recent articles by G.F. White (1994) and G.O.P. Obasi (1994) in the Bulletin of the American Meteorological Society also present important information on research efforts aimed at reducing natural disasters.

Interestingly, the number of United States deaths caused by natural weather disasters has declined during the latter part of this century while the dollar value of property damaged has increased dramatically. The reason this is so, seems to be fairly obvious. Weather forecasters are constantly improving their ability to alert people about impending severe storms, such as tropical storms and hurricanes. Moreover, evacuation procedures have been developed to move people from threatened areas. These changes have resulted in fewer injuries and deaths.

However, people do continue to live in and move to areas prone to floods and tropical storms. Because many people want to live or vacation at the shore, new construction occurs along many vulnerable coastal areas. When a powerful storm eventually strikes these densely populated areas, catastrophic damage is going to occur, regardless of whether global warming has occurred or not.

In summary, to date, despite increased concentrations of carbon dioxide and other greenhouse gases in the atmosphere, the Earth’s climate has not warmed significantly. Moreover, we have found no convincing evidence that the number and intensity of extreme weather events has increased in recent years. Indeed, were global warming to take place, it is unlikely that potentially dangerous storms, such as hurricanes would increase in number or intensity.

In conclusion, it would be prudent for the scientific community to carefully monitor atmospheric temperatures, especially by using satellite measurement systems. Developmental work on mathematical climate models should continue. Scientists should also under take more detailed observational studies of the temporal and spatial distribution of historically anomalous weather events. Observational programs for other real and potential global warming forcing functions such as sea surface temperature, ocean circulations, and aerosols should also be implemented on a much broader scale and in more detail than they are at present.

Text references for this study

Norman J. Macdonald, M.S., is a Certified Consulting Meterologist and former Senior Meterologist at Accu-Weather. Joseph P. Sobel, Ph.D., is a Senior Vice-President at Accu-Weather. Accu-Weather is the world’s leading commercial weather firm.