Today's report outlines a series of options to prevent the worst from occurring.
"We have a really monumental challenge on our hands," Vicki Arroyo of the Pew Center on Global Climate Change in Arlington, Virginia, said in a telephone interview.
Scientists and policymakers have argued over which options to emphasize in the fight against global warming. For example, many environmental groups are concerned about hazardous waste from nuclear energy if that option is widely promoted.
But given the immensity of the challenge, Arroyo said, the "luxury" to ignore any of the available options does not exist.
"We really need to tackle this problem from every angle we can," she said.
Daniel Kammen directs the Renewable and Appropriate Energy Laboratory at the University of California, Berkeley. He said in a telephone interview that the market has yet to show which methods will prevail.
"The critical issue isn't to pick and choose too much but is to say, if the governments are going to listen to this report as they should, there is actually a large number of technologies that are available to explore and look at," he said.
Some of the technologies are ready to enter the marketplace now, he added, while others will require further research.
Kammen and Arroyo both said that the cost to the global economy of acting now to curb greenhouse gas emissions is far less than doing nothing.
(Get the facts about global warming.)
Economics and Caps
The new report also assesses the likely economic effects of stabilizing the concentration of greenhouse gases in the atmosphere.
The lower the concentration of gases, the lower the impact of global warming but the greater the brunt to global economic activity, the scientists conclude.
(Learn how global warming works.)
According to the report, stabilization of greenhouse gases at the low end of the range—445 parts per million—would limit global temperature rise to about 3.6 degrees Fahrenheit (2 degrees Celsius).
Doing so, however, requires a reduction of greenhouse gas emissions by 50 to 85 percent by the middle of this century.
Achieving this would shave about 0.12 percent off global gross domestic product (GDP) each year, panel co-chair Bert Metz explained at the briefing.
Stabilization at the high end of the range—710 parts per million—would see a temperature rise as high as 7.2 degrees Fahrenheit (4 degrees Celsius) and allow greenhouse gas emissions to increase 10 to 60 percent by 2050.
This scenario would blunt GDP by about 0.06 percent a year.
Officials in China, the U.S., and India fear that the most aggressive cuts would slow economic growth too much and had reportedly pressed for their nations to be excluded from the report.
The University of California's Kammen said such fears are "false."
Though the U.S. and China are the world's top two consumers of coal, a particularly dirty fossil fuel, the countries also happen to have ample biofuel and wind resources.
"So the switch-off job is not as hard as many people are portraying," he said.
In a statement released today, the environmental group WWF said the IPCC report shows it is clearly possible to stop global warming if action is taken now.
"The IPCC has delivered a road map for keeping the planet safe. Now it's the turn of politicians to do more than just pay lip service," said Hans Verlome, director of the group's climate change program.
"We can stop climate change before it's too late."
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