In an open letter to the American people released Tuesday, 76 American Nobel Laureates in science endorsed Democratic Senator Barack Obama of Illinois for president of the United States. This is the largest number of Nobel prize winners ever to endorse a

United Nations Secretary General Ban Ki Moon has warned that without a comprehensive international agreement to reduce the greenhouse gas emissions that lead to global warming, humanity faces "oblivion."

The glory of winning the Nobel peace prize will not propel Al Gore into a challenge for the US presidency, he said today. The former vice-President had been urged to mount a late bid for the Democratic nomination but, asked if the prestigious award might

George Bush's top scientific advisor has delivered the strongest statement yet from within the US administration that greenhouse gas emissions caused by human activity are to blame for climate change.

Al Gore, the former U.S. vice president-turned-environmentalist, said Thursday that he hoped to push the environmental agenda to the forefront of the 2008 U.S. presidential election -- but probably not as a candidate.

President Bush told reporters last week that his administration is not considering any new action to put mandatory caps on greenhouse gas emissions, despite a U.S. Supreme Court decision mandating the establishment of such regulations.