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The scientific case for an international climate treaty rests largely on predictions generated by computer programs known as general circulation models (GCMs). The models attempt to forecast the climatic effects of increases in atmospheric concentrations of carbon dioxide and other “greenhouse” (heat-trapping) gases.
Modeling — a form of hypothesis building — is an important part of atmospheric science. But the real test of any scientific hypothesis is experiment, or at the very least, observation — empirical evidence. Dr. Roy Spencer of NASA and Dr. John Christy of the University of Alabama in Huntsville are uniquely qualified to address the empirical side of the global warming debate. In 1996, they received a Special Award from the American Meteorological Society “for developing a global, precise record of earth’s temperature from operational polar-orbiting satellites, fundamentally advancing our ability to monitor climate.”
To acquaint Washington-based policy makers and journalists with their work, CEI, on behalf of the Cooler Heads Coalition, invited Drs. Spencer and Christy to lecture on global warming and the evidence from the satellite record. They spoke at a coalition sponsored science briefing at the Hertiage Foundation on June 19, 1998. The following pages are a lightly edited transcript of their presentations and the ensuing question and answer period.
If the GCMs were correct, several things should have happened or be happening. The planet should have warmed 1.5°C over the past century; the past two decades should have seen the most rapid warming; and the upper troposphere should be moistening, that is, experiencing “positive water vapor feedback.” (Water vapor is the main greenhouse gas. Without positive water vapor feedback, the relatively small increase in heat energy due to man-made emissions cannot produce significant global warming.)
Various empirical observations either contradict or fail to confirm the aforementioned hypotheses. Surface instruments indicate the world has warmed 0.5°C over the past century — about one-third what the models project. The satellites show no warming trend during the past 19 years — a finding independently validated by weather balloon observations. Satellite measurements also reveal that the upper troposphere above the tropics, the warmest and wettest region on earth, is remarkably dry. As yet, there is no physical evidence of positive water vapor feedback.
Marlo LewisVice President for Policy and Coalitions