After two reports predicting a warmer Earth where life is fundamentally changed, a U.N.-sponsored scientific panel next month will issue a third study describing how a united world can avert the worst, by embracing technologies ranging from nuclear power to manure controls.

Under a best-case scenario for heading off severe damage, the global economy might lose as little as 3 percentage points of growth by 2030 in deploying technologies to reduce greenhouse-gas emissions, says the panel's draft report, obtained by The Associated Press.

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But it won't be easy.

"Governments, businesses and individuals all need to be pulling in the same direction," said British researcher Rachel Warren, one of the report's authors.

For one thing, the governments of such major emitters as the United States, China and India will have to join the Kyoto Protocol countries of Europe and Japan in imposing cutbacks in carbon dioxide and other heat-trapping gases emitted by industry, power plants and other sources.

The Bush administration rejected the protocol's mandatory cuts, contending they would slow U.S. economic growth too much. China and other poorer developing countries were exempted from the 1997 pact, but most expected growth in greenhouse emissions will come from the developing world.

The draft report from the Intergovernmental Panel on Climate Change (IPCC), whose final version is to be issued in Bangkok on May 4, says emissions can be cut below current levels if the world shifts away from carbon-heavy fuels like coal, embraces energy efficiency and significantly reduces deforestation.

"The opportunities, the technology are there and now it's a case of encouraging the increased use of these technologies," said International Energy Agency analyst Ralph Sims, another of the 33 scientists who drafted the report.

Two previous IPCC reports this year painted a dire picture of a future in which unabated greenhouse emissions could drive global temperatures up as much as 6 degrees Celsius (11 degrees Fahrenheit) by 2100. Even a 2-degree-Celsius (3.6-degree-Fahrenheit) rise could subject up to 2 billion people to water shortages by 2050 and threaten extinction for 20 percent to 30 percent of the world's species, the IPCC said.

The third report makes clear the world must quickly embrace a basket of technological options — both already available and developing — just to keep the temperature rise to 2 degrees Celsius (3.6 degrees Fahrenheit).

The draft notes that significant cuts could come from making buildings more energy-efficient, especially in the developing world, through better insulation, lighting and other steps, and by converting from coal to natural gas, nuclear power and renewable energy such as wind, solar and biofuels.

Less significant but also important would be steps to make motor vehicles more fuel-efficient, reduce deforestation, and plant more trees as a carbon "sink," absorbing carbon dioxide. Even capturing methane emitted by livestock and its manure would help, the report says.

Over the next century, it says, such technology as hydrogen-powered fuel cells, advanced hybrid and electric vehicles with better batteries, and carbon sequestration — whereby carbon emissions are stored underground — will become more commercially feasible.

It says taking "optimal" mitigation measures might by 2030 stabilize greenhouse-gas concentrations in the atmosphere at 445 to 534 parts per million, up from an estimated 430 ppm today.

It indicates that stabilizing concentrations relatively quickly at 450 ppm — an unlikely scenario — might keep the temperature rise to 2 degrees Celsius (3.6 degrees Fahrenheit) over preindustrial temperatures, a level scientists think might avert severe damage.

Achieving the 445-534 ppm range might cost under 3 percent of global gross domestic product ( GDP) over two decades, the draft says.

That compares favorably to global economic growth that every year has averaged almost 3 percent since 2000. The damage from unabated climate change, meanwhile, might eventually cost the global economy between 5 and 20 percent of GDP every year, according to a British government report last year.

The IPCC draft notes, however, that its cost estimate is based on a "relatively small" number of studies and would require all nations to join in those best-case mitigation efforts, and that "barriers to implementation of mitigation options are manifold."

The report says governments could lower economic costs if low-carbon technologies are promoted via carbon taxes or "cap-and-trade" systems like Europe's, whereby industry is allocated emissions quotas, which can then be traded among more efficient and less efficient companies.

Turning the report into reality, authors acknowledge, will require a significant shift in political will among some large economies. The last IPCC assessment, in 2001, also called for introduction of many of the same technologies, but they so far haven't been widely embraced.

"I've been involved in this game for 35 years. We're not progressing as quickly as we could or should," Sims said.

The draft notes, in fact, that current government funding for most energy research programs is about half what it was in 1980.