Inordinate contention attends complex socio-technical problems like global warming. The polarized extremes (end of the world versus good for us) are, I believe, the two lowest probability cases, yet they dominate media and political debates and editorial pages. No responsible scientist would claim to have precise expectations about our climatic future, its implications for nature and our lives or the costs of doing something about it. Nevertheless, a great deal of consensus exists about many aspects of the topic, despite the large uncertainties which accompany other components.
A half-dozen pieces of circumstantial evidence were sufficient for the 100-scientist Intergovernmental Panel on Climate Change (IPCC) to assert in 1995: "the balance of evidence suggests that there is a discernible human influence on global climate". The 2000AD IPCC assessment, while strengthening this conclusion based on five more years data and analysis, has brought to the forefront a new discernible statement: this time that recent observations of regional climate changes and the movements of wildlife, marine systems, ice extent and the timing of vegetation life cycles are becoming clear enough in the past few decades--very likely to be the warmest in at least 1000years---that there now appears to be a discernible impact of regional climatic variations on natural systems.
The prime implications of this new finding is that as the climate continues to change--and change may be expected to accelerate substantially in the 21st century--we can expect natural systems to become highly stressed. I will try to distinguish which are the well known components of the debate, contrast them to the over-contentious media/political debate, and put this problem in the context of so-called Integrated Assessment of policy responses to the advent or prospect of global warming.
International scientific assessments have for decades emphasized the necessity of treating uncertainties in their reports to governments contemplating policy options to deal with the advent or prospect of human-induced climatic changes. The most recent Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR) is now completed, and unlike previous reports there is a formal guidance paper(prepared by Richard Moss and Stephen Schneider after three rounds of review) which recommends strategies to explicitly account for uncertainties. Although some might expect this to be welcome news to scientists, a number of authors--particularly physical scientists from developed countries--have somewhat resisted the notion of expressing quantitative subjective probabilities to characterize uncertainty. Nevertheless, without probabilities atttached (even highly subjective ones), any outcomes projected cannot be put into a risk-management framework, and the nature of this conundrum will be highlighted.
About the speaker:
Stephen Schneider is a Professor in the Department of Biological Sciences and a Senior Fellow at the Institute for International Studies at Stanford University. He is editor of Climatic Change and the Encyclopedia of Climate and Weather and the lead author of several IPCC chapters and the IPCC guidance paper on uncertainties.
Stephen Schneider published an essay in the January 2002 issue of Scientific American which gives critical review of a portion of Bjørn Lomborg's controversial book, The Skeptical Environmentalist.
Contact information:
Stephen Schneider
Stanford University
shs@stanford.edu