THE HYPE ABOUT HYDROGENgreenhouse gasses . . . due to human activities continue to alter the atmosphere in ways that are expected to aVect the climate.�The ipcc added that here is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.�7 Some have argued that natural factors such as variations in sunshine and volcanic eruptions, which have strongly influenced temperatures in past centuries, are the source of recent temperature trends, but more recent analysis has shown that these factors can explain only about one-quarter of the warming since 1900.18 President George W. Bush asked the National Academy of Sciences for a report on climate change and on the conclusions of the ipcc assessments. In June 2001, the eleven-member blue-ribbon panel, which included experts previously considered skeptical about global warming, unanimously concluded: reenhouse gases are accumulating in Earth atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising.�The panel noted that he ipcc conclusion that most of the observed warming of the last 50 years is likely to have been due to the increase in greenhouse gas concentrations accurately reflects the current thinking of the scientific community on this issue. The stated degree of confidence in the ipcc assessment is higher today than it was 10, or even 5 years ago.�9 Commenting on the steady stream of peer-reviewed reports and articles documenting global climate change appearing in his journal and others, Science editor-in-chief, Donald Kennedy, said in 2001, onsensus as strong as the one that has developed around this topic is rare in science.�0 The third reason why so many developed countries (and leading companies) are willing to pursue strong action to reduce greenhouse gas emissions is the dire news: The best scientific models project that the current path of rapidly increasing emissions will lead to changes in the global climate both dramatic and unpleasant. As the National Academy of Sciences noted in 2001, limate change simulations for the period of 1990 to 2100 based on the ipcc emissions scenarios yield a globally-averaged surface temperature increase by the end of the century of 1.4 to 5.8c (2.5 to130TLFeBOOK
