Summary: Climate science is not "settled;" it is both uncertain and incomplete. The available observations do not support the mathematical models that predict a substantial global warming and form the basis for a control policy on greenhouse (GH) gas emissions. We need a more targeted program of climate research to settle major scientific problems.
1) The fate of anthropogenic CO2 in the atmosphere is uncertain: its uptake into the ocean; the biological pump; the missing carbon sink. The future growth of atmospheric CO2 depends crucially on estimates of residence time and the amount of fossil fuels likely to be used for energy production. Some researchers suggest an 8x pre-industrial value, while others doubt whether CO2 will even double.
2) The temperature record of the last hundred years is of poor quality and shows many discrepancies. Surface temperatures disagree with recent measurements from satellites and balloons. The urban heat island effect may skew the record.
3) General Circulation Models (GCMs) vary by 300% in their temperature forecasts, require arbitrary adjustments, and cannot handle crucial mesoscale and microscale cloud processes. Their forecasts of substantial warming depend on a positive feedback from atmospheric water vapor (WV).
4) GCMs cannot account for past observations: the temperature rise between 1920 to 1940, the cooling to 1975, and the absence of warming in the satellite record since 1979. Various explanations need to be explored: reduced positive feedback from WV; increase in cloudiness; anthropogenic aerosols; man-made land changes; increasing air traffic; solar variations influencing climate.
5) Prehistoric climate fluctuations, on timescales as rapid as a decade, are prevalent – as judged from the data from tree rings, sediments, and ice cores. Such climate events are not explained by existing models, nor can current GCMs account for El-Nino events, the North Atlantic Oscillation, and other contemporary rapid changes in climate.
6) Sea level (SL) rise is a major feared impact of a future warming. It seems likely, however, that increased evaporation from the ocean may lead to more rapid accumulation of polar ice and a lowering of sea level. This possibility is supported by an observed inverse correlation between SL rate of rise and tropical sea surface temperature (SST).
7) Severe storms and hurricanes have diminished in the past 50 years. A global warming trend is calculated to reduce the latitudinal temperature gradient and therefore the driving force for storms and severe weather.
8) Global agriculture will likely benefit from climate warming and increased precipitation; increased CO2 leads to more rapid plant growth; increased nocturnal and winter warming leads to a longer growing season. Farmers can and will adjust to climate changes.
9) The spread of disease vectors, like malaria-carrying mosquitos, is likely to be unimportant in comparison to human vectors. In addition, medical science and insect control technology are sure to progress.
10) Historical evidence supports the idea that warmer climate intervals are beneficial for human activities, food production, and health. Cold periods have had the opposite effect.
11) Mitigation techniques are available that can slow down the rise of atmospheric GH gases and a possible climate change: energy conservation and increased efficiency often make economic sense; hydro and nuclear power are available now; solar energy may be around the corner; tree planting and ocean fertilization may be low-cost methods of sequestering atmospheric CO2.
12) Policy measures should be applied with great caution and only when justified by scientific data, lest they create more harm than good. In particular, mandatory controls on energy use by whatever method can create great economic losses, impacting especially on poor people and poor nations.
The UN Framework Convention on Climate Change (FCCC) states that "...policies and measures to deal with climate change should be cost-effective so as to insure global benefits at the lowest cost" (Article 3.3). The FCCC calls for an "economic system that would lead to sustainable economic growth and development" (Article 3.5). The convention also calls for periodic review as scientific knowledge and information grow.
Article 2 states the FCCC objective, namely the "stabilization of GH gas concentrations ... that would prevent dangerous anthropogenic interference with the climate system." We should note that science cannot as yet define what that level is -- whether the present level, or some future level, or the pre-industrial level. Defining “dangerous” levels is a daunting task for climate science, and should be tackled before far-reaching policies are put in place.
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