The climate change bill that senators are to begin debating next week is a hugely important signal of intent on behalf of U.S. legislators. Yes, negotiations could still alter the legislation. But the bill's core proposition is correct: Unless the United States radically reduces its greenhouse gas emissions, along with other major emitters, the damage to the climate will be irreversible.

Radical reduction is unlikely to happen through voluntary action alone. Measures in the bill, through a mandatory cap-and-trade scheme, would reduce emissions 70 percent from 2005 levels by 2050. These cuts would be based on a carbon market incentive system that moves with the grain of action around the globe.

Over the past few years, the debate on climate change has shifted profoundly. The scientific consensus that human activity is causing global warming has become overwhelming. The effect of unabated climate change is shocking and, as was shown by the report of Sir Nicholas Stern -- the first authoritative study of the economics of climate change, commissioned by the British government in 2006 -- it is far riskier economically to ignore climate change than to act to abate it.

For full essay:
Leading On Climate Change
How Action in Congress Can Move the World
By Tony Blair
Washington Post
Thursday, May 29, 2008; A19

The writer was British prime minister from 1997 to 2007. He recently launched the Breaking the Climate Deadlock initiative to promote a new global agreement on climate change.