In a letter to Nature (March 13, 1997) James W. Hurrell and Kevin E. Trenberth questioned the reliability of the satellite temperature data which show a slight cooling trend over the last 20 years. They argue that the data contain significant discontinuities due to various factors, the most important being the replacement of worn out satellites. The main contention in the Hurrell/Trenberth paper is that there are two “spurious” downward jumps in the satellite record due to changes in satellites and that the real temperature trend is slightly positive.
There are some serious errors with the method used by Hurrell and Trenberth, however. Drs. John R. Christy, Roy W. Spencer, and William D. Braswell, who track and publish the satellite temperature data, point out those errors in correspondence to Nature (September 25, 1997).
There are two methods to directly measure the temperature of the lower troposphere (surface to 7 km). One is balloon-borne instruments known as radiosondes which rise through the atmosphere. The other are microwave sounding units (MSUs) mounted on satellites which measure the intensities of microwave emissions from atmospheric oxygen which are proportional to temperature.
There is strong agreement between the two records even over the periods where Hurrell and Trenberth claim that the spurious jumps take place. Another data set is also available from the NOAA-06 and NOAA-07 satellites which were measuring temperatures at the time of the breaks that Hurrell and Trenberth claim to have discovered. These also agree with the MSU data.
Hurrell and Trenberth ignore the balloon data and estimate atmospheric temperatures using sea-surface temperatures (SSTs). There are a couple of problems with this method, however. First, the regions where Hurrell and Trenberth find the greatest disagreement is in the Pacific and Indian Oceans where ship data are scattered. Buoy data have also been available since the early-1980s. But, as Christy points out in correspondence with The Cooler Heads Newsletter, “the SST dataset is not homogeneous for these critical regions. Ships and buoys do not measure the water temperature to the agreement necessary for the types of variations we look at for climate change over a decade or so.”
Second, Hurrell and Trenberth derive atmospheric temperatures from the SSTs using general circulation models (GCMs). Christy argues that “There is considerable evidence that SSTs and the atmospheric temperature do not behave in the rigid fashion believed by Hurrell and Trenberth and represented by their simple [linear] regression model. Several studies show that for long periods of (months to years) there are differences between SSTs and air temperatures due to the natural variability of the vertical structure of the atmosphere.”
Once again advocates of the global warming hypothesis use imperfect models to attack actual observed data, standing the scientific method on its head. In the past, when data contradicted the models, the models were rejected. With highly politicized global warming science, however, empirical evidence that contradicts the politically predetermined outcome is either ignored or explained away as anomalous.
What Do Scientists Say?
A survey of state climatologists by Citizens for a Sound Economy found that there is little support for the global warming hypothesis. When asked if they agreed with the statement by President Clinton, “The overwhelming balance of evidence and scientific opinion is that it is no longer a theory but now a fact, that global warming is for real. There is ample evidence that human activities are already disrupting the global climate.” 36 percent agreed, while 58 percent disagreed.
Asked whether “recent global warming is largely a natural phenomenon,” 44 percent said yes while 17 percent said no. Nine out of ten surveyed agreed that “scientific evidence indicates variations in global temperature are likely to be naturally-occurring and cyclical over very long periods of time.” Eighty-nine percent of the climatologists agreed that “current science is unable to isolate and measure variations in global temperatures caused only by man-made factors,” and 61 percent said that the historical data do not indicate “that fluctuations in global temperatures are attributable to human influences such as burning fossil fuels.”
Sixty percent of the respondents said that reducing man-made CO2 emissions by 15 percent below 1990 levels would not prevent global temperatures from rising, and 86 percent said that reducing emissions to 1990 levels would not prevent rising temperatures. Finally, by a 39 to 33 percent margin, more climatologists say that, “evidence exists to suggest that the earth is headed for another glacial period.” The survey can be found at www.cse.org/cse/ and www.globalwarming.org.
What Does the Science Say?
Dr. S. Fred Singer of the Science and Environmental Policy Project has just released a overview of the current state of climate change science and asks whether drastic reductions in greenhouse gases are justified.
The objective of a global climate treaty would be to prevent “dangerous interference with the climate system.” But, according to Singer, there is no scientific evidence that would suggest what level of interference would be dangerous. An article appearing in Science argued that 350-400 ppm is a dangerous level of CO2. However, they base this on an arbitrary “dangerous” temperature increase of 2 degrees C.
Singer also challenges the claim in the 1996 report of the Intergovernmental Panel on Climate Change (IPCC) that it is now possible to discern the human influence among the noise on climate change. First, the “natural” variations are derived from computer models rather than actual observations. Second, the computer models exclude the cooling effects of mineral dust and of smoke and soot from burning biomass and the cloud production effects of sulfate aerosols.
Singer also contends that warmer weather would be beneficial to mankind. Warmer global temperatures, the models predict, would reduce the temperature gap between the northern and southern hemispheres reducing storm intensity at the mid-latitudes. Northern hurricanes, for example, have fallen in both frequency and intensity over the last 50 years. Rainfall has fallen worldwide for the last 40 years. As for rising sea levels Singer argues that they are correlated with falling temperatures.
Singer concludes there is little evidence to justify drastic reductions of greenhouse gases. The best way to avoid the adverse effects of climate change is to adapt. He notes that societies that are economically advanced are the least affected by changes in climate and more readily adapt to changes. Economic development (which will require greater emissions) then is necessary if we are to avoid adverse effects which may arise from climate change. The report is available by contacting SEPP at (703) 352-7535 or by e-mail at singer@sepp.org.