The United States and China surprised even the most hardened environmental activists on Wednesday when President Barack Obama and Chinese President Xi Jinping announced a joint agreement to significantly reduce greenhouse gas emissions over the next 15 years.

The agreement, announced at the end of the Asia-Pacific Economic Cooperation (APEC) summit, sets goals more ambitious than those previously established in either country. It also sends an important message to the rest of the world ahead of U.N. climate talks in Paris next year: If two of the world’s largest greenhouse gas emitters are willing to cut back, it’s time the rest of the international community takes climate action seriously.

Environmentalists, nonetheless, point out the agreement is non-binding and its language is vague. The announcement proclaims that both countries want to reduce emissions, but it leaves out exactly how that will happen. The glaring absences may ultimately render the document more of a symbolic commitment than a road map for the future of sustainable energy.

“A lot of us see it as a step in the right direction, but we’re planning to send the message that this isn’t enough,” said Karthik Ganapathy, the U.S. communications director of 350.org, a network of grassroots climate action groups. “It’s a nonbinding agreement so now we have to set policy to put this plan into action.”

The U.S. part of the plan calls for a 26 to 28 percent reduction of greenhouse gas emissions by 2025 based on 2005 levels. That’s a big increase from Obama’s earlier goal of reducing emissions 17 percent by 2020.

The Chinese side of the agreement skirts commitments to cutting emissions in favor of capping them, saying that China will commit to ensuring its emissions begin falling by 2030.

“It’s a big deal,” said Erika Rosenthal, the international climate attorney for EarthJustice, a group of environmental lawyers. “The world’s two biggest carbon emitters have really set an enormously encouraging tone.”

Less reassuring to environmentalists are the agreement’s descriptions of how the U.S. and China will meet their ambitious goals. Controversial technologies like coal carbon sequestration are mentioned, but renewable technologies are barely touched upon. To some, the fine print of the document doesn’t match its goals.

The agreement runs about 1,000 words, and only two of them are given to renewable energy technologies. (The two are “solar energy,” in the context of supporting pilot programs for new forms of energy.) By contrast, nearly 200 words are given to technologies supported by the U.S.-China Clean Energy Research Center, a joint diplomatic venture that was established to study how to manufacture buildings, cars and power plants more efficiently. A large part of that research effort is dedicated to “clean coal” technology, which involves scrubbing coal of its most polluting elements and then capturing carbon produced by burning coal and burying it underground.

One of the U.S.’s biggest experiments with clean coal is a $5 billion coal power plant in Mississippi that has yet to open and is already over budget. The energy it will produce will cost several times more than other forms of energy, according to the Sierra Club.

If that is one of the main methods China and the U.S. plan to use to cut emissions, some say the countries are in for a reality check.

“The goals set here, those are incompatible with investments in fossil fuel infrastructure,” said Ganapathy. “[Clean coal] is just biting around the edges of the problem.”

Another section of the agreement mentions natural gas production as a way to reduce emissions. But not mentioned in the agreement is methane, the powerful gas that can make natural gas drilling a bigger greenhouse gas emitter than coal if not properly controlled.

“We continue to be concerned about methane,” said Wenonah Hauter, the director of environmental group Food and Water Watch. “That’s being ignored in this agreement, which means this action is just more promotion of fracking under the guise of climate action.”

Others questioned the ability of the Obama administration to move toward using more green energy, given the gridlock over climate action in Congress. The president’s most ambitious climate policies, namely directing the U.S. Environmental Protection Agency to limit the amount of carbon power plants are allowed to produce, have all been accomplished through executive action.

Sen. Mitch McConnell, R-Ky., on Wednesday called Obama’s plan “unrealistic” and said it would “ensure higher utility rates and far fewer jobs.” Rhetoric like that, as well as the switch in the Senate from Democratic to Republican control, will make any ambitious action on climate difficult to achieve.

That may mean all of the reductions outlined in the agreement come in the form of more executive actions. Whether the Obama administration has the political will to take those steps ahead of the 2016 presidential election remains to be seen.

“Meeting these goals will mean an economywide effort to find places to reduce emissions,” said John Coequyt, the international climate programs director at the Sierra Club. “It means further reductions from vehicles, it means tackling methane emissions from natural gas production. To reach these targets, it can’t just be business as usual.”