William Yeatman

No Link Between Global Warming and Malaria

A new study in the February 21 issue of Nature tests the proposition that higher incidences of malaria in the East African highlands are caused by global warming. The studys authors, led by Simon Hay at Oxford University, could not find a link between the two phenomena.

The study examines the long term trends in meteorological data from four East African sites that have recently experienced a significant resurgence in malaria cases. As noted in the study, “The suitability of each month for Plasmodium falciparum malaria transmission depends on a combination of temperature and rainfall conditions.” The researchers looked for changes in these climate variables that might explain changes in the incidence of malaria.

What they found was that “Temperature, rainfall, vapor pressure, and the number of months suitable for P. falciparum transmission have not changed significantly during the past century or during the period of reported malaria resurgence.” These findings are not “consistent with the simplistic notion that recent malaria resurgences in these areas are caused by rising temperatures.”

The studys authors explain that there are several other factors that have contributed to the resurgence of malaria in East Africa, including antimalarial drug resistance, population migration, and breakdowns in public health and vector control operations. Thus, according to the authors, “Economic, social and political factors can therefore explain recent resurgences in malaria and other mosquito-borne diseases with no need to invoke climate change.”

Two recent studies cast doubts on the claim that global warming could lead to increased climate variability and to the cessation of the climatically important thermohaline circulation (THC). The THC is a conveyer-like circulation in the Atlantic Ocean where “Near-surface currents bring warm, saline waters from the subtropics to high northern latitudes where they are cooled by the atmosphere, sink to depths between 2,000 and 3,000 meters, and flow back south as a deep western boundary current,” according to the study in Science (February 22, 2002).

This circulation is important because, “The ocean affects climate through its high heat capacity relative to the surrounding land, thereby moderating daily, seasonal and interannual temperature fluctuations, and through its ability to transport heat from one location to another,” as noted in the study appearing in Nature (February 21, 2002). If the THC were to cease, it would lead to dramatic cooling in Europe.

The Nature study states that, “Most, but not all, coupled GCM [global circulation model] projections of the twenty-first century climate show a reduction in the strength of the Atlantic overturning circulation with increasing concentrations of greenhouse gases if the warming is strong enough and sustained long enough, a complete collapse cannot be excluded.”

But due to model deficiencies and uncertainties about how the climate system responds to greenhouse forcings, it is difficult to determine the likelihood of future changes in the THC. To remedy this problem, the authors believe that scientists should examine the palaeoclimate record, which “provides the fundamental basis for evaluating the ability of models to correctly simulate behavior of the THC.”

What the palaeoclimate record shows us is that abrupt climate changes due to changes in the THC are not characteristic of the current warm interglacial period known as the Holocene. But such changes “were characteristic of the last glaciation.” The authors conclude that, “The palaeoclimate data and the model results indicate that the stability of the thermohaline circulation depends on the mean climate state.” Since abrupt changes are confined to glacial periods and not characteristic of interglacial periods it is unlikely that global warming will have any effect on the THC.

The study appearing in Science attempts to find an explanation for abrupt climate changes that have been discovered in the palaeoclimate data. The study notes that, “In contrast to the relatively stable climate of the past 10,000 years, during glacial times the North Atlantic region experienced large-amplitude transitions between cold (stadial) and warm (interstadial) states.”

Using climate models, the authors determine that “reduced calving of icebergs into the North Atlantic after a widespread ice sheet surge constitutes a trigger for the rapid glacial warming events,” which follow a few hundred years later.

In other words, ice sheet surges during glacial periods are characterized by rapid calving of icebergs that inject fresh water into the North Atlantic, reducing salinity. The resulting fall in sea water density prevents sinking, which then stops the THC.

The rapid calving that follows the ice sheet surge causes the ice streams to retreat from the coastline, and calving eventually ceases. Over time, the absence of freshwater input leads to greater salinity and the THC starts up again leading to an abrupt warming.

Both of these studies demonstrate that, contrary to climate model predictions, a warmer climate is more stable and that colder glacial climates are subject to significant climate variability and more extreme weather events.

The authors examine the oxygen isotope profiles of excavated otoliths “aragonite structures in fish used for acoustic perception and balance” from Peruvian sea catfish. Because the oxygen that is incorporated into the otoliths is in isotopic equilibrium with the seawater, scientists can use them to derive past sea surface temperatures.

What they found was that during the mid-Holocene, from around 6,000 years ago, sea surface temperatures were three to four degrees C higher than they were over the decade of the 1990s. The authors cite several studies that show that El Nio conditions did not exist prior to 5,000 years ago, which mean that warm sea surface temperature are likely to reduce El Nio activity rather than heighten it.

Canadas environment minister, David Anderson, recently requested that his colleagues in the cabinet begin driving small, more fuel efficient cars. According to the Guardian of London (March 4, 2002), “His fellow cabinet members ignored him, or muttered about the symbolic importance of being chauffeured around in big (meaning prestigious) cars.”

“The Liberal government talks the talk, but will not drive the drive,” said acting Canadian Alliance leader John Reynolds in the House of Commons. “How can the prime minister or the minister of the environment expect Canadians to sacrifice so much for the sake of Kyoto when his own ministers will not even trade their taxpayer-funded cars for environmentally-friendly vehicles?”

A new study appearing in Physica A (302: 2001), tests the accuracy of climate models and finds them lacking. The problem, say the authors, is that the models do not adequately take into account persistence in the climate system.

This issue of persistence is another reason why “separating the anthropogenic forcing from the natural variability of the atmosphere may prove to be a major challenge since the anthropogenic signal may project onto and therefore be hidden in the modes of natural climate variability.”

The authors tested several models. “We are interested,” they write, “in the way the models can reproduce the actual data regarding (a) trends and (b) long-range correlations. Of course, we cannot expect the models to reproduce local trends like urban warming or short-term correlation structures. But long-range correlations show characteristic universal features that are actually independent of the local environment around a station. So we can expect that successful models with good prognostic features will be able to reproduce them.”

“It turns out,” according to the study, “that the models considered display wide performance differences and actually fail to reproduce the universal power law behavior of persistence. It seems that the models tend to underestimate persistence while overestimating trends, and this fact may imply that the models exaggerate the expected global warming of the atmosphere.”

Al Kamen in his “In the Loop” column in the February 15 Washington Post: “The Bush White House excels at keeping secrets from the press, opponents, and, sometimes, even friends, judging from a somewhat testy exchange Wednesday evening when White House Council on Environmental Quality aides and others briefed a dozen or so senior GOP congressional staff members on the administrations new environmental package.

“The Hill folks protested that they had not been consulted about the package beforehand. When the White House disagreed, one Hill aide apparently asked for a show of hands from those whod been consulted. None went up, were told. Then talking points were distributed. Bushs goal of reducing our greenhouse gas intensity by _____ will reduce overall U.S. emission by _____ million metric tons by 2012, one point said, calling it an extremely ambitious, yet realistic goal.

“Numbers would help, the Hill team said. After some reluctance, the numbers were supplied. Its like the Wheel of Fortune: you can buy a vowel, you can buy a number.”

Studies Find More Model Weaknesses

Two studies appearing in the February 1 issue of Science give further evidence that climate models are still wholly inadequate to predict future climate change. Using satellite data from the last two decades, a team of researchers led by Bruce A. Wielicki with NASAs Langley Research Center found that, “The top-of-atmosphere (TOA) tropical radiative energy budget is much more dynamic and variable than previously thought.”

The study explains that, “Earths climate system is driven by a radiative energy balance between the solar or shortwave radiation absorbed by Earth and the thermal infrared or longwave radiation emitted back to space.” For the Earths climate to remain unchanged, this energy budget must equal zero. “The TOA radiation budget,” says the study, “is crucial in determining climate variability and feedbacks.” It also provides a rigorous test of the ability of climate models to represent the atmospheres physical processes.

The data show that there was a drop in longwave radiation of about 2 W/m2 (watts per square meter) from the late 1970s to the mid 1980s followed by a rise of about 4 W/m2 from the mid 1980s to the late 1990s. “Because radiative forcings of 1 W/m2 or less are important for climate change prediction, natural variability of 4 W/m2 in the longwave part of the tropical radiation budget is considered a major change.”

The researchers argue that this is not likely due to global warming since, “The flux changes are far too large to be explained by the small surface and atmosphere warming over this time period, which will tend to be offset by increased CO2 and water vapor greenhouse gas trapping.”

More importantly, however, “These changes are sufficiently large that, in principle, they should be seen in climate model predictions.” The researchers tested five different models, including the well known Hadley Centre and National Center for Atmospheric Research models. They found that “There is remarkably little variation in the tropical mean fluxes from the models when compared to the data.”

The other study attempts to answer the question of whether the changes observed in the satellite data in the Earths radiative balance over the last two decades are the result of natural variability or manmade global warming. The researchers, Junye Chen, Barbara E. Carlson, and Anthony D. Del Genio, with NASAs Goddard Institute for Space Studies, found that the “Earth has been radiating more heat and reflecting less sunlight in the region from 30 degrees S to 30 degrees N over the past decade, the net result being more energy leaving the tropics.”

This change is due to a strengthening of two different tropical circulations known as the Hadley cell and the Walker cell. “Equatorial convective regions,” say the researchers, “have intensified the upward motion and moistened, while both the equatorial and subtropical subsidence regions have become drier and less cloudy.”

So whats the upshot? “The possibility that lapse rates were decreasing instead [of increasing] before 1980 suggests that the observed intensification of the Hadley-Walker cell may be due to natural variability on decadal or longer time scales rather than to a forced climate change.”

The National Assessment stated, “Much of the recent warming occurred suddenly around 1977, coincident with the most recent of the large-scale Arctic atmosphere and ocean regime shifts.” What the report failed to mention, however, is that the global circulation models it used to make its predictions show a gradual warming due to higher concentrations of carbon dioxide, not sudden jumps.

The cause of the 1977 climate jump was a phenomenon known as the Pacific Decadal Oscillation. As explained by Baliunas and Soon, “The Pacific Ocean temperature changes naturally on multiple time scales. The major pattern in the northern Pacific Ocean is for it to hold at a low average temperature for roughly 20 to 30 years, and then to suddenly shift upward, where it remains for some decades. Then it shifts back down again.”

This is a pattern that has been directly measured for the last 100 years. The pattern has also been observed in temperature data derived from tree rings, and reaches back at least 1,000 years. Moreover, a look at the temperature data in Alaska after 1977 shows that 22 of the 30 locations from which Alaskas temperature is measured have experienced “either no warming or a significant cooling trend.”