Introduction to Part

Michael C. MacCracken

For nearly 100 years following 1897, when Svante Arrhenius first made a quantitative estimate of how human-caused emissions of carbon dioxide (CO2) would affect the climate, the presumption was that changes in the climate would occur slowly and that, therefore, society would have decades to develop the policies to slow and then stop climate change. When the President's Science Advisory Council advised President Lyndon Johnson in 1965 that climate change was an important emerging issue, there was no urgency expressed to deal with it. Similarly, assessments by the US National Academy of Sciences and various US government agencies summarized scientific understanding in the 1970s and 1980s, changes in climate that could make a difference to the environment and society seemed many decades off, especially in that observations were not convincingly showing any climatic response to the increasing concentrations of CO2 and other greenhouse gases.

That the Earth's climate could change significantly over quite short periods, however, became particularly evident as a result of analyses of high-resolution ice cores from the Greenland Ice Sheet. Not only did these cores document the long-term changes that were seen in the low-resolution cores drilled in ocean sediments, but they suggested that abrupt changes in climate (at least over Greenland and the North Atlantic) were not even rare events, at least during times when there was substantial glacial ice and meltwater that could, in ways not yet completely understood, lead to rapid changes in ocean conditions.

At the same time, detection and attribution studies aimed at identifying the human 'fingerprint' of climate change found that, indeed, the climate was changing in ways that could only be explained by human activities. Studies brought together in the assessments of the Intergovernmental Panel on Climate Change (IPCC) made clear that both human-caused increases in the atmospheric loading of sulfate aerosols and natural variations in solar radiation and volcanic aerosols were actually countering the warming influences of the increasing concentrations of greenhouse gases, delaying observation of their strong warming influence. What these studies are suggesting is that there is a stronger potential for changes in the climate (and, in that climate is simply the average of the weather, for changes in the weather) than has been recognized in past scientific assessments.

The three chapters in this section explore various aspects of this issue. In Chapter 1, countering the oft-heard criticisms of media-hyped naysayers that the IPCC's estimates of climate change are too high, Dr A. Barrie Pittock presents ten reasons, each much more soundly argued than the criticisms, that the modelbased projections of climate change summarized by the IPCC are likely to be underestimating the amount of climate change we can expect. In Chapter 2, Dr Judith Curry summarizes the observational evidence indicating that tropical cyclones (i.e. hurricanes and typhoons) are becoming more intense and destructive than projections with relatively coarse grid models have indicated, suggesting that the pace of increasing damage in coastal regions could continue to accelerate rapidly. In Chapter 3, with the pace of temperature change and of storm intensity both seeming likely to increase more rapidly than had been indicated, Dr Devra Davis and John Topping describe the types of health impacts that the accelerating pace of climate change is likely to cause, making clear that significant effort will need to be put towards enhancing public health infrastructure and practices in order to satisfactorily limit increasing societal vulnerability.

These findings and others from around the world are making it more and more clear that there is an increasing risk that the pace of climate change is accelerating, and that, because of the high degree of environmental and societal vulnerability, the potential for very serious impacts is becoming more and more likely.

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