On Tuesday, China and the United States announced an unprecedented plan to work together to fight global warming. The deal includes new trade partnerships and significant new greenhouse gas goals for both countries. The US pledged to cut its emissions by up to 28 percent by 2025, while China agreed that its emissions would peak around 2030 and promised to get one-fifth of its power from non-fossil-fuel energy sources by the same year. Environmental groups have roundly welcomed the plan as an important step. But critics of the deal—including congressional Republicans—say China has been let off lightly and that it won’t follow through with its commitments.