Sciencepolicy Challenge

The Intergovernmental Panel on Climate Change (IPCC) has concluded that if atmospheric concentrations of greenhouse gases continue to increase, largely as a result of fossil fuel combustion, agricultural practices, and deforestation, average temperatures will increase at a rate much faster than our world has experienced since the last Ice Age. This in itself represents a vision of the future that is substantially different from the past. It challenges long held notions of climate stability, slow rates of climate change (in human terms), and the dominance of natural forces over societal forces in influencing global climate.

Even as new evidence is presented about how civilizations over the last 5000 to 7000 years have been affected by changes in climate (Lamb, 1982), it is recognized that those historic shifts in annual temperatures were only around ± l to 2°C from current global averages. The medieval warm epoch of the tenth to thirteenth centuries was around 0.5 to 1°C above the current global average, while the Little Ice Age of the sixteenth to nineteenth centuries was around 1°C cooler. Although ancient and medieval civilizations may have been less technologically developed than twentieth-century society, modern individuals and nations still have to plan for and adapt to climate. Impacts associated with recent extreme events and El Niño episodes illustrate that despite technological advances, societies in developed and developing countries are still vulnerable to short-term variations in climate (Burton, 1997). There has been a clear upward trend in weather-related costs to insurance companies since the 1960s (Munich Re, 2000), leading to substantial losses by major reinsurance companies such as Lloyd's (IPCC, 1996a). This does not include uninsured losses that may be equal in magnitude to insured losses.

Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts, Edited by Thomas D. Potter and Bradley R. Colman. ISBN 0-471-21489-2 © 2003 John Wiley & Sons, Inc.

A warming of up to 5.8°C during the twenty-first century, a rate of up to 0.5° per decade, would be unprecedented in human history (IPCC, 2001 a). Such a change in mean temperatures, with accompanying changes in seasons and probabilities of extreme events, would have direct impacts on land, water, wildlife, and a myriad of indirect impacts on communities, businesses, and governments. If greenhouse gas emissions are not reduced, societies would be faced with the prospect of having to adapt to a new climate that current climate models are not yet able to precisely describe, especially at the regional scale. Adaptation in the twenty-first-century context would be a very different challenge than the one faced by our ancestors, and the costs of adaptation measures are not known.

Identifying societal impacts of a scenario of rapid warming is a complex interdisciplinary research activity that goes beyond assessments of changes in atmospheric processes alone. These changes would be superimposed on changing populations, landscapes, institutions, technologies, and perceptions of resources and environment.

What are the broad dimensions of the societal aspects of global climate change? An outline is presented in Figure 1. This chain of causality also represents a target for a research activity known as integrated assessment (IA). Several research groups have attempted to incorporate part or all of this chain into a series of linked models, which collectively have become known as integrated assessment models (IAM). The

Public & private economic and social activities; domestic and international

Consumption of energy & materials; generation of waste products; land use change

Greenhouse gas emissions

Ambient concentrations of greenhouse gases in the atmosphere

Changes in climate and sea level

Direct & indirect impacts on ecosystems and people; regional variations according to unique circumstances & vulnerabilities

Economic & social valuation of impacts

Figure 1 Science-policy dimensions of climate change. Mitigation responses focus on emission reduction or sink enhancement. Adaptation responses focus on reduction of vulnerabilities to climatic events or taking advantage of new climate-related opportunities.

3 methodology for impact assessment of climate change scenarios 905

IPCC lists 23 IAMs in its Second Assessment Report (IPCC, 1996b). Other IA techniques include economic models, decision support models, expert judgment exercises, policy exercises, and the use of themes or places as an interdisciplinary platform for collection and analysis of information (Cohen, 1997; Schneider, 1999; Kasemir et al., 1999).

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