The United States and China — the world's two largest economies, which are together responsible for nearly half of all annual global greenhouse gas emissions — announced a historic pledge on Wednesday to address climate change. President Barack Obama promised to cut US emissions from 2005 levels by 26-28 percent by 2025 and President Xi Jinping announced that China's emissions would peak by 2030. To reach this goal, China must bring online 800-1000 gigawatts of new renewable energy, enough added power to serve the electricity needs of the entire United States.
While widely praised for helping to advance efforts to achieve an international climate agreement late next year, some environmental groups and diplomats have criticized China's emission reduction pledge for not going far enough. But in this rush to judgment, critics are overlooking that the details of China's plan for reducing its carbon pollution are in some places extremely thin or entirely absent.
A key part of the US-China climate pledge is that both countries agree to a long-term development path, which each nation claims is consistent with keeping global temperatures from rising two degrees Celsius above the pre-industrial average — a goal the United Nations Intergovernmental Panel on Climate Change says is necessary in order to avoid the most dangerous impacts of climate change.
'The world has been waiting for this.'
But several experts who spoke with VICE News wonder how the combined pledges will help achieve the two-degree goal.
"Although the governments might be able to claim that the commitments could limit the warming from the beginning to the end of the 21st century to be no more than two degrees," Minqi Li, an economics professor at the University of Utah, told VICE New, "they are ignoring the warming up to the 21st century and the future warming beyond the 21st century. That would not be an honest climate commitment."
Li calculates that, even with these new commitments, temperatures might rise more than three degrees over the long run.
Still unknown is what the peak level of China's carbon dioxide emissions will be.
"There are huge uncertainties within China's 2030 peaking goal," the Worldwatch Institute's Habing Ma told VICE News. "For instance, with what kind of trajectory will China achieve its emission peak — steep or flat? This will result in significantly different outcomes both in terms of the final peaking amount of emission and the accumulated emissions from now to 2030. Those two factors will obviously have a huge impact on the global two-degree target."
Also unknown is whether China's emissions will remain flat or decrease after peaking. A 2011 report from the Lawrence Berkeley National Lab predicts a post-peak "flattening" in China, which is not consistent with achieving the two-degree goal.
Zou Ji, deputy director of China's National Center for Climate Change Strategy believes that while some think China can do better, a 2030 peak will be difficult. He says efforts to peak early could cause an economic recession or even destabilize the Chinese economy.
"The manufacturing market is expected to be saturated by about 2020 and output will naturally peak then," he said, "but construction and transportation are still going to consume huge quantities of energy and thus create emissions. This, and household consumption, present big challenges for China."
The US and China both wanted a public announcement in which their respective leaders appeared to be challenging the other to act. And the joint announcement has been widely celebrated as achieving that goal. But there remain many areas of disagreement between the two countries that will likely continue to plague cooperation on climate change, say experts.
One issue that could upend future partnership is the question of which country should take more responsibility for the climate problem. The United Nations Framework Convention on Climate Change (UNFCCC), which both the US and China are parties, says nations have a "common but differentiated responsibility" — CBDR in UN jargon — for acting to reduce the amount of greenhouse gases they produce.
China has consistently said that the US, as a developed nation, which has historically emitted far more carbon pollution, should take the lead on addressing climate change. As a developing nation, says China, its primary challenge is poverty eradication and economic development.
UN climate talks for the last five years have been derailed, in part, because of this dispute over responsibility for climate change and, say observers, it will likely remain a major hurdle for diplomats later this month when they meet in Lima, Peru and in Paris, France next year.
"The CBDR question is indeed interesting." Angel Hsu, a China expert at Yale University, told VICE News. "China will of course say that these new statements are in line with CBDR principles in that they are still going to grow emissions overall until 2030, still allowing for further future development."
Despite the unknowns of China's future emissions pathway and continued areas of disagreement between it and the US, the joint announcement is seen as an important political breakthrough and one that was essential for advancing international negotiations.
"The point here is that the two major emitters have agreed and will watch each other," Gary Yohe, professor of Economics and Environmental Studies at Wesleyan University told VICE News. "The world has been waiting for this."
Follow Lucia Green-Weiskel on Twitter: @LuciaGGW