Human and ecological systems are already vulnerable to a range of environmental pressures, including climate extremes and variability. Global warming is likely to amplify the effects of other pressures and to disrupt our lives in numerous ways. Signific ant impacts on our health, the vitality of forests and other natural areas, the distribution of freshwater supplies, and the productivity of agriculture are among the probable consequences of climate change.

On a business as usual path, the world is headed to concentrations far higher than have been observed during the time of human civilization and to levels not seen on the planet for millions of years--and all in one century, a geologic "blink of an eye." The faster the rate of change in climate, the less time there will be for both ecological and socio-economic systems to adapt and the greater the potential for "surprises" or unanticipated events. Given the long time lags between cause and effect and bet ween effect and remedy, a prudent course of action is to slow the rate of change. Investing now to protect Earth's climate will enable our children and grandchildren to live in a world that is not dramatically altered by an enhanced greenhouse effect.