The focus of the debate on climate change has shifted drastically in the past several years. The Kyoto Protocol was signed in 1997 on the assumption that climate change and global warming were being caused by emissions of carbon dioxide and other greenhouse gases.
Many scientists challenged this assumption, however, saying it was not fully substantiated. American experts in particular argued that early action was not needed. They favored "delayed actions" 20 to 30 years down the road. They based their position on the prevailing concentration of atmospheric CO2 at the time — only 360 parts per million, compared with the estimated danger level beginning at 550 ppm.
On March 24, 2001, U.S. President George W. Bush announced his decision to withdraw from the Kyoto Protocol. He said the protocol was based on a short-term perspective, would prevent the development of large-scale technologies, and would negatively impact medium- to long-term strategies to fight global warming.