The report did acknowledge that the climate may be less sensitive to carbon dioxide emissions than was stated in 2007.
The full 2,000-page report isn't going to be released until Monday.
The IPCC assessments are important because they form the scientific basis of U.N. negotiations on a new climate deal for cutting emissions. Governments are supposed to finish that agreement in 2015, but it's unclear whether they will commit to the cuts that scientists say are need to avoid the worst effects of climate change.
The report presented four scenarios with different emissions controls. In the best possible case, with strict pollution controls, temperatures could only rise by as little as half a degree Fahrenheit (0.3 degrees Celsius) by 2100. The middle scenarios show increases in the 3 to 4 degree range F (2 degrees C). The worst case is somewhere between 5 and nearly 9 degrees F (2.6 degrees to 4.8 degrees C).
In the past, the world has spewed more greenhouse gases than even the amounts used to calculate the worst-case pathway in earlier reports.
Scientists said the latest versions of the scenarios show there is hope, albeit faint, that the worst of climate change can be avoided.
"We presented four possible futures," said climate scientist Jerry Meehl of the U.S. National Center for Atmospheric Research. "It's up to the governments to decide which future we embark upon. We can achieve a low climate change future. It is possible. In theory."
Borenstein reported from Washington.
The Intergovernmental Panel on Climate Change report: http://www.ipcc.ch/report/ar5/wg1/
Karl Ritter can be reached on https://twitter.com/karl_ritter
Seth Borenstein can be followed at http://twitter.com/borenbears
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