The newly announced landmark plans by the U.S. and China to limit their greenhouse gas emissions left open the question of how realistic the targets are. The plans feature a number of ambitious goals for each nation, but they face serious challenges. A look at the status of the climate change fight in the two countries, the new goals, and the feasibility of achieving them:
What are the U.S. goals?
The U.S. plans to double its pace of emissions reduction to meet a targeted decline of 26% to 28% from 2005 levels by 2025.
How feasible is it for the U.S. to achieve that target, from a technical standpoint?
The Obama administration has said that the building blocks are in place to achieve the reductions the president promised. Central to the effort is the plan to cut emissions over the next 16 years from power plants, the single biggest source of heat-trapping carbon dioxide, by 30% from 2005 levels.
The administration is also reducing emissions from cars and light trucks and plans to add limits for heavy trucks. The Environmental Protection Agency is also expected to roll out measures in the coming weeks to address methane emissions from the oil and gas industry. It is working to phase out the use of hydrofluorocarbons, or HFCs, gases used as coolants in consumer goods and propellants in aerosols. The EPA could also move to cut greenhouse gases from oil refineries.
What are the major political obstacles?
Republicans, who will take control of Congress in January, are expected to fight those steps, and the energy industry is suing to block new rules.
Administration officials say they will not have to turn to Congress, but can instead tighten rules already proposed. They could require, for instance, a 40% — rather than 30% — reduction in power plant emissions by 2030, analysts say. New measures that would help the U.S. hit its emissions reduction goal by 2025 are poised to draw an even more virulent political backlash, because they would affect industries beyond the power sector, such as oil and gas and manufacturing.
Such ambitious goals also are "going to be really tough to meet without new laws," which would require congressional action, said Michael Levi of the Council on Foreign Relations.
What are the Chinese goals?
China plans to shift its economy away from coal-fired power generation and create a network of zero-emission plants, including nuclear and renewables, that is larger than the entire U.S. electrical grid.
What are the major obstacles?
At first glance, it appears that China, as an authoritarian state, has the tools to make industries and localities comply with new rules. But its efforts to get local leaders to follow through on imperatives such as pollution reduction and fair labor practices have made spotty progress, suggesting that emissions cuts might also prove tough to enforce, said Mary E. Gallagher, associate professor of political science at the University of Michigan.
China's impetus for addressing carbon pollution stems from its own domestic realities, analysts say. Besides corruption, air pollution from the combustion of fossil fuels is the single biggest domestic issue the government faces, Gallagher said.
Cutting fossil fuel use to address climate change would also clean the air. But the government has had a hard time getting localities and the industries with which they are allied to act on anything besides economic growth, in part because promotion in Communist Party ranks is tied to economic output. Companies have pollution-control equipment but often keep it idle because of the expense and extra work, Gallagher said.
"In the U.S., the trick is to get the laws passed but then you can assure their effective implementation," Gallagher said. "In China, they will pass laws but they could fail with implementation. Our two political systems have bottlenecks at different places."
Another challenge is the scale of the alternative-energy infrastructure China plans to build within a relatively short period.
How will it be confirmed that China is actually trying to cut emissions?
An accountability standard has yet to be put in place, but it is part of international talks to draft a climate change plan in Paris next year. The Chinese about-face on climate caught many people off guard and gave rise to speculation, especially among conservatives, that its pledge is empty and that Obama was duped.
Yet China's plan to hit a peak in its greenhouse gas pollution within 15 years and then curtail it afterward is an enormous step. Where that peak will be, however, is unclear, though important. Will China's pollution be 15% above 2005 levels when it finally scales back? Or will it be more like 40%?
Will the deal put the planet on track to avoid the worst consequences of global warming?
In a word, no. To avert the worst disasters, global average temperatures must be kept from rising by 2 degrees Celsius (3.6 degrees Fahrenheit) from the average temperatures in pre-industrial times 150 years ago.
The American and Chinese initiatives, even when taken with a recent European Union announcement to cut its emissions by 40% by 2030, are not enough in and of themselves. Other big emitters, most notably India and Russia, must make similarly ambitious cuts.
Further, so much warming has been baked into the atmosphere through more than two decades of squabbling over emissions cuts that much deeper reductions would need to occur fast. In the case of the U.S., that would amount to a 70% cut in emissions from 1990 levels by 2030, an all-but-impossible goal over the next 15 years.
But Wednesday's announcement is "a down payment" on meeting the 2-degree goal, the first of many steps needed to rein in emissions, said Alden Meyer, director of strategy at the Union of Concerned Scientists.