While the IPCC refines its models, other scientists report extensive empirical evidence of warming and its effects. Earlier this year, one team reconstructed surface temperatures in the northern hemisphere over the past millennium and found that the 20th century has been the warmest by far. Other studies have found the 1990s to be the warmest decade and 1998 the warmest year on record. Still more evidence of warming has been found in the receding of snow at higher mountain elevations, the thinning of the polar ice caps, the bleaching of coral reefs in the tropics, and the migration of butterflies, sea birds and even crustacea, from temperate areas toward the poles. In December 1997, industrialised countries, which have been responsible for most greenhouse gas emissions, agreed to reduce emissions to five percent below their 1990 levels by the year 2012.
Some scientists consider that step to be extremely modest, bordering on insignificant.
But the administration of President Bill Clinton, which signed on to that target, has declined to send it to the US Senate for ratification because it knows that the measure faces certain defeat there. Many lawmakers, especially those who receive substantial contributions from oil, gas and coal interests, insist that global warming is only a theory and that Washington should wait until it receives positive proof before taking preventive measures that could adversely affect the US economy. The Pew Centre is taking out advertisements based on its latest study in The New York Times, Washington Post, Newsweek and two publications widely read in Congress, Roll Call and National Journal. The group was set up precisely to provide more information about the accumulating evidence of climate change and its impact on the United States. The Pew study differs from the earlier IPCC estimates mainly because it assumes that sulphur dioxide emissions will not be as great as previously anticipated, due to efforts by national governments to reduce air pollution and acid rain.