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Abstract: A Climate of Doubt about Global Warming

Director, Office of Climatology, Arizona State University, Tempe, Arizona

Over the past decade global warming has become a front-page environmental issue capturing the attention of thousands of scientists and policy makers worldwide. According to numerical models of climate, the continued buildup of greenhouse gases will lead to a substantial rise in planetary temperature, melting icecaps and alpine glaciers, rising sea levels, changes in regional climate patterns, and an increase in extreme weather events. Empiricists have noted that the planetary temperature, as measured from thermometers throughout the globe, has increased over the past century thereby providing support for the theoretical predictions of the models. Many nations have called for action to combat the threat of global warming, and the Kyoto Protocol represents a major first step in the policy arena.

However, many of the most fundamental global warming issues remain in a state of considerable debate in the scientific community. For example, in the most recent half decade, the atmospheric concentration of many greenhouse gases has slowed or even stabilized. The numerical models of the climate continue to have serious weaknesses, including their representation of cloud processes and the coupling of the atmosphere and ocean. Thermometer records may show warming, but serious concerns remain about the true representativeness of their readings. In addition, increased output of the sun, lack of recent volcanism, and trends in El NiƱo/southern oscillation have certainly contributed to any observed warming. The entire issue is further complicated by the fact that satellite-based and balloon-based measurements of lower atmospheric temperatures show no warming whatsoever over the past few decades. Furthermore, there appears to be no increase in tropical cyclone activity, severe weather events, or variability of climate.

We now fully realize that the future climate will be impacted by many changes in atmospheric composition, including the buildup of greenhouse gases. Increasing levels of sulfate and mineral aerosols and the depletion of stratospheric ozone all have a known cooling effect that may completely cancel any projected warming. Finally, the evidence is overwhelming that the climate impact of a fully implemented Kyoto Protocol will be trivial over the next 50 years.

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