One chief concern, domestically and internationally, is cost. The president, speaking at the United Nations last month, encouraged countries to help developing nations meet emissions targets. But according to the New York Times, some economists estimate that a new climate agreement could cost up to $100 billion a year by 2020, with some putting the number even higher, at up to $1 trillion.
Developing nations, such as India, are hesitant to jump on board the international bandwagon because of such concerns. China, the largest emitter of greenhouse gases, has also been less than eager to commit.
In the United States, the House climate bill, co-sponsored by Rep. Henry Waxman, D-Calif., and Rep. Edward Markey, D-Mass., has faced some backlash. Critics say it would increase costs for companies that have to pay a fine for emitting greenhouse gases above certain levels. Utilities and other industries that emit heat-trapping gases would have to buy permits for their emissions, and they will be able to trade pollution permits between themselves. There will also be a similar program for hydrofluorocarbons.
This "cap and trade" system was first set up for sulfur dioxide by the 1990 Clean Air Act Amendment, which many environmentalists consider a milestone in recent history.
On Wednesday, director of the bipartisan Congressional Budget Office, Doug Elmendorf, told senators the cap and trade system is a cost effective way to reduce emissions, but that these provisions would reduce U.S. GDP by roughly half a percent in 2020 and by between 1 to 3 percent by 2050. He added that real GDP will be roughly two and a half times as large in 2050 as it is today, so those changes would be comparatively modest.
Other criticis say new climate change legislation will cost Americans their jobs as the focus switches to more green jobs and clean technology.
"The bigger challenge is making sure that the costs aren't concentrated on particular vulnerable people and that's what a lot of the legislation effort has been aimed at," Levi said.
Supporters of the bill say the cost of inaction exceeds the material costs.
"When you look at the entire picture, the costs were remarkely low and they don't kick in until 2020. If you look at the costs of inaction besides that, it becomes a very compelling action," Fox said.
Despite the challenges facing the administration in meeting expectations and dealing with critics, proponents of tougher climate change rules say the Obama administration has taken big leaps ahead from the previous administration.
"The contrast with the Bush administration is very strong," Levi said. "They took some constructive steps in the last couple of years of the administration, but the domestic efforts the Obama administration is pursuing are sharply different than what the Bush administration was after."
Experts say the Bush administration was especially quiet on the international front, and Obama's rhetoric -- even if it's just that so far -- still shows a commitment to the issue and hence, has earned him praise.
"Under the prior administration, the U.S. government was generally seen as the biggest impediment to an international agreement," Gerrard said. "Today, the U.S. government clearly wants an international agreement. The big question will be how far along the road toward domestic regulation will we be when Copenhagen takes place."