"We have to begin the conversation about cruising past 2 degrees, because we're on course for that," said John Podesta, who chairs the liberal think tank Center for American Progress. "It's hard to contemplate and scary to contemplate, but it has to be addressed at this point."
Vanderbilt Law School professor Michael Vandenbergh said today's leaders will be judged harshly by future generations for not focusing on climate change.
"A hundred years from now, they're not going to be talking about health care or the fiscal cliff," he said. "But they will ask, 'What did you do when we knew we were going to have serious climate change?' "
John R. Christy, who directs the Earth System Science Center at the University of Alabama in Huntsville, said some researchers are exaggerating the severity of the threat. He said that the right climate target is "in the mind of the beholder," given that rising energy demand is a sign that many poor people are struggling "to be lifted out of their current condition."
"No one in Washington can stop that," he said. "And, right now, carbon is the most accessible and affordable way to supply that energy — so CO2 emissions will continue to rise because of the undeniable benefit carbon energy brings to human life."
Last year, the United States experienced several weather events — including extreme storms, a historic drought and wildfires — that many scientists say can be exacerbated by climate change.
Some scientists, however, think it is premature to blame droughts or hurricanes on human-caused warming. Georgia Institute of Technology atmospheric scientist Judith A. Curry said in an email that the global average temperature for 2012 will not set a record — last year will probably be the ninth warmest. "Natural variability continues to dominate the occurrence of extreme weather events," she said.