The world needs to divert substantially from today's main energy sources within a few decades to limit centuries of rising temperatures and seas driven by the buildup of heat-trapping emissions in the air, the top body studying climate change has concluded.





''We can no longer make the excuse that we need to wait for more science, or the excuse that we need to wait for more technologies and policy knowledge,'' said Adil Najam, an author of one chapter and an associate professor of international negotiation at the Fletcher School at Tufts University. ''To me the big message is that we now have both and we do not need to wait any longer.''


Carbon dioxide is particularly important not only because so much is produced each year -- about 25 billion tons -- but because much of it persists in the atmosphere, building like unpaid credit card debt.

To stop the rise, report authors said, countries would need to expand adoption of existing policies that can cut emissions -- like a fuel tax or the binding limits set by the Kyoto Protocol -- while also increasing research seeking new energy options. This work would include pushing for advances in solar and nuclear power.


According to several authors, the final version estimates that bringing global carbon dioxide emissions by 2030 to levels measured in 2000 would require a cost on released carbon dioxide of $50 to $100 a ton, roughly on a par -- in terms of fossil fuel prices -- of an additional 25 cents to 50 cents for a gallon of gasoline.

The report projects that this shift might cause a small blunting of global economic activity, resulting in an overall reduction of perhaps one-tenth of a percentage point per year through 2100 in the world's total economic activity, the authors said.




''Here in the early years of the 21st century, we're looking for an energy revolution that's as comprehensive as the one that occurred at the beginning of the 20th century when we went from gaslight and horse-drawn carriages to light bulbs and automobiles,'' Dr. Moomaw said. ''In 1905, only 3 percent of homes had electricity. Right now, 3 percent is about the same range as the amount of renewable energy we have today. None of us can predict the future any more than we could in 1905, but that suggests to me it may not be impossible to make that kind of revolution again.''