ABSTRACT
As we enter a new century, it is apparent that people have already altered the climates in which they live and will alter them even more dramatically in the coming decades. We know from the Third Assessment of the Intergovernmental Panel on Climate Change (IPCC, 2001) that over the past century average surface temperatures across the globe have increased by 0.6°C, and we now have stronger evidence that human activities are responsible for most of this warming. We also know that the 1990s were the warmest decade and 1998 was the warmest single year since 1861. These ongoing and future changes in climate will continue to alter nature's life-support systems for human life in many parts of the globe: through an ongoing rise in global average sea level, increases in precipitation over most mid- and high-latitudes of the northern hemisphere, increased intensity and frequency of droughts, floods and severe storms, and as yet unforeseen abrupt changes and extreme climatic events. Meanwhile, decades will pass before the current human efforts to reduce ongoing climate change will register their effects. In short, time is at a premium. The impacts of these human-induced changes in climate, although in their early stages, are showing up in shrinking glaciers, thawing permafrost regions, longer growing seasons in mid- and high-latitude agricultural areas, shifts in plant and animal ranges and declines in some plant and animal populations. But these effects now in progress only suggest the much more far-reaching changes likely to come. Major global warming threats to human security and well-being across the planet include diverse risks and some potential benefits (see Box 16.1).
