The United States and China announced a historic climate-change agreement on Wednesday. The leaders of the world’s two largest greenhouse gas emitters promised to cap carbon pollution in 15 to 20 years. Here’s a quick rundown:

1. What Does It Mean for Climate?

It’s a good start. China agreed to halt the growth of its carbon emissions around 2030. If it meets that commitment, the country’s CO2 pollution will probably plateau at around 11 billion metric tons. For our part, the United States agreed to emit between 26 percent and 28 percent less CO2 by 2025 than we did in 2005, when we produced 7.1 billion metric tons of carbon. The reduction would place the United States’ 2030 emissions at a shade over five billion metric tons.

Now, take a look at this chart, produced by the Australian government:

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To have a 50-50 chance of staying beneath the maximum global temperature increase of 2 degrees Celsius (about 4 degrees Fahrenheit) announced as a target at the 2009 Copenhagen climate summit, global annual emissions by 2030 should stay beneath 30 billion metric tons. China and the United States will emit more than half of that total, even if they fulfill their new commitments. That means every other country has to share the remaining 14 billion metric tons.

That’s not impossible—China and the States accounted for 45 percent of global emissions in 2013—but it would be a challenge. Developed countries, like those in the European Union, have already cut emissions, and it will be hard for them to maintain that pace of reduction for the next 15 years. In developing nations, continued population and economic growth will be major obstacles. India, the world’s third-largest carbon emitter, is building hundreds of new coal-fired power plants. Its share of global emissions will almost certainly rise by 2030.

So the U.S.-China carbon emissions agreement is a building block, but it’s not a complete solution. Still, those who closely follow international climate negotiations praised it, saying it could help break the impasse that threatened to stall progress toward a worldwide deal at talks in Paris late next year. (Many nations weren’t willing to make commitments without action from China and the United States.)

“Our announcement can inject momentum into the global climate negotiations,” Secretary of State John Kerry wrote in an op-ed for the New York Times.

2. Can Both Countries Meet the Targets?

Yes. In 2011, researchers at Lawrence Berkeley National Laboratory predicted that China’s emissions would peak in approximately 2030, even without any official government commitment. Population growth is slowing, and the economic growth rate is leveling off. The rapid adoption of cars, refrigerators, and other energy-consuming technologies will also slow as it reaches a saturation point among the growing middle class. China’s long planned shift toward renewable energy and natural gas will also help. This year, the country will install more solar panels than the United States has in its entire history.

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Illustrated by: EPA

The United States’ reduction commitment is more of a stretch, but it’s still achievable if we stay on the current path. Two years ago, the Obama administration imposed ambitious automobile fuel-efficiency standards, dictating that the average vehicle travel 54.5 miles per gallon by 2025—an 83 percent improvement over current standards. In June, the U.S. Environmental Protection Agency proposed emissions limits for existing power plants that would achieve a 30 percent reduction in carbon pollution by 2030, compared to 2005 levels.

Taken together, those plans will go a long way toward meeting the new U.S. commitment; electricity generation and transportation account for 60 percent of U.S. greenhouse gas emissions.

3. What Happens If We Don’t Meet the Targets?

Other than a much warmer climate, rising seas, accelerated species extinction, and more intense storms? Not much. The agreement contains no consequences for failure by either country, and there is no international court designated to hear disputes about the agreement. It’s a promise, not a legally binding treaty.

4. So What’s the Point?

This agreement marks the first time a developing country has agreed to limit its carbon emissions. Many up-and-coming economies have resisted such limits, fearing that a carbon cap would restrain their growth and ability to improve living standards. Others argue that it’s fundamentally unfair to ask poor countries to contribute to the solution when they have contributed so little to the problem to this point.

China’s commitment begins to undermine those arguments against action. Yvo de Boer, the former executive secretary of the United Nations Framework Convention on Climate Change, called the agreement “a first critical step to unlocking the logjam in the climate-change negotiations.” With the next climate-change summit, in Paris, about one year away, the agreement puts pressure not only on developing countries like India but also puts the spotlight on Australia, Japan, and Canada, which have been moving slowly or—in the case of Canada, which was the first country to formally abandon the Kyoto Protocol in 2011—backwards in addressing climate change.

5. What Are the Do-Nothings Saying About the Agreement?

U.S. politicians who oppose cutting our country’s emissions often argue that the real problem comes from China, India, and Russia, and that we could and should do nothing until those countries make the first move. The Climate Desk documented this line of argument in an amusing video:


So, these people are celebrating China’s historic pledge to limit carbon emissions, right? Not exactly. Senator Mitch McConnell says the agreement “requires the Chinese to do nothing at all for 16 years.” Senator James Inhofe takes a vastly different view, arguing that the Chinese commitment is so challenging, the country will never be able to fulfill it. He called the promise “hollow and not believable” and a “non-binding charade.”

Climate-change deniers aren’t quite on the same page yet—perhaps the sudden announcement of the agreement prevented them from huddling with their messaging team. The only thing that’s clear is that their resistance to addressing climate change was never really about China.