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Section III Climate Change

33

Climate Change

Introduction..................................................................................................283

Natural Causes of Climate Change............................................................284

Human Causes of Climate Change............................................................285

Climate Models.............................................................................................286

Detecting and Attributing Climate Change..............................................289

Conclusion....................................................................................................291

Robert L. Wilby References......................................................................................................291

University of Loughborough Bibliography..................................................................................................292

Introduction

Climate change is an abstract concept in the sense that no one can feel a 30-year average rainfall total or global mean temperature. Yet these types of indexes are widely used by scientists to describe the state of the climate system (Figure 33.1). However, climate averages are accumulated from day-to-day weather, which is perceptible, as are meteorological variations from pole to the equator or from sea level to summit. Retreating ice sheets, increasing ocean heat content, and rising sea levels are further manifestations of a warming planet.

Climate change is also a plastic concept, because the term means very different things to different people.1'1 More than a century ago, atmospheric warming linked to “carbonic acid” (now termed carbon

Global annual mean temperature anomalies

FIGURE 33.1 Global annual mean temperature anomalies (black line) based on analyses of surface data (HadCRUT4) showing lower and upper bounds of the 95% confidence interval of the combined effects of measurement and sampling, bias, and coverage uncertainties (gray lines). Annual anomalies are calculated with respect to the 1961-1990 mean. Source: UK Met Office, http://www.metoffice.gov.uk/hadobs/hadcrut4/.

dioxide or C02) was regarded by Arrhenius as beneficial by delaying the onset of the next ice age.121 In contrast, many modern-day governments and their citizens view climate change as a present and/ or imminent threat to be managed. Others do not see the same urgency or question whether current (policy and economic) responses are proportionate to the established risk.

This entry begins with an overview of the natural and human drivers of climate variability and change over decades to millennia. Global climate models and their projections are then described. The final section considers the technical challenges surrounding formal detection and attribution of climate change. These are all areas of rapid scientific development and vigorous debate.

 
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