"A 50 percent cut from today's levels in 50 years is almost certainly not enough to prevent very dangerous and very expensive climate change and that's according to almost all of the world's leading scientists and the IPCC report," Downie said. "You can get a 50 percent cut in 2050 if all the cuts come late. Then, you haven't done a lot to prevent very dangerous change. ... We could have a climatic and environmental disaster on our hands in 2050 and beyond."
Many scientists have called for even greater reductions -- an 80 percent decrease by 2050 -- but as climate prediction models change, so does that number.
Still, Downie isn't all pessimistic. He does see the summit, which he called a "modest first step," as a jumping off point for more stringent guidelines in future negotiations, including the next U.N. climate conference set for Copenhagen in the fall of 2009.
"This is more of a symbolic G-8 announcement that will be used as a starting point for discussion and not as an endpoint," Downie said. "It begins to establish more of a bargaining range. It signals to the Chinese and Indians that the Americans are going to be serious participants in a global discussion and are willing to go first and agree to significant cuts. Do I think it's important to say is this a nice step? Yes. The Europeans got the Bush administration to say that these global goals are a good idea."
According to Downie, at the U.N. meeting countries are likely to set interim goals for reductions by 2020 to get global warming reductions set into motion. He envisioned a version of the European Union's 20-20 proposal to reduce greenhouse gas emissions by 20 percent in 2020.
"I think there will be an agreement. Will it be effective enough to prevent the worst aspects of climate change? That's unclear," he said.
Despite the headlines the announcement garnered, Downie cautioned against praising grand goals without plans to back them up.
"It should be clear to everyone this is a bunch of people who are leaders of a country. It in no way represents actual policy," he said. "It will only be meaningful if it's translated into policy, and it will only be effective if it's translated into policy stronger than this current announcement."
Similarly, Sierra Club spokesman David Willett doubted that the G-8's goals would affect the political fight stateside for stemming climate change.
"It's good that people are talking about these issues on this global stage. ... If the question is does an agreement on the G-8 level have any effect on our senate? No. I think that's going to have to come from demand from the American people," Willett said. "I think that people want action taken on global warming, but the discussion on the G-8 level probably doesn't change the game in the United States."
To make a difference in climate change, goals should be even more aggressive, said Jonathan Overpeck, director of the Institute for the Study of Planet Earth at the University of Arizona, who characterized the G-8's goals as "toothless."
"There are many parts of the climate system that appear to be changing even faster than our models predict they should -- Arctic ice, changes in great ice sheets," he said. "These things are going faster than we thought possible and that just highlights the need to act and to act very aggressively as soon as we can on greenhouse gas emissions."
"[But] there are scientists who think that might not be enough," he continued. "I'm afraid they might be right."