If Republicans win six seats on Tuesday, they control the Senate. And President Barack Obama’s environmental legacy will be their top target.

More than anything else, Mitch McConnell has campaigned to keep his seat and become the next Senate Majority Leader by promising to end the Environmental Protection Agency’s regulations on carbon pollution from power plants. The EPA is within its authority to regulate greenhouse gasses—the Supreme Court has already decided that. But Republicans can still block this and other EPA regulations by attaching riders to appropriations bills prohibiting the EPA from enforcing its rules. Or Republicans could achieve a similar effect by simply stalling the EPA—like passing proposed legislation that would require several government agencies to certify carbon regulations will come at no cost to the economy. They also will try to force Obama to approve the controversial Keystone XL pipeline and prevent new rules by the EPA that clarify the Clean Water Act.

But a GOP-controlled Senate might aim even higher—at the international United Nations body that will host negotiations on cutting greenhouse gas emissions next year in Paris. The Washington Examiner’s Zac Colman reported that Republicans would like to cut U.S. funding for the UN Framework Convention on Climate Change and the international body of climate change scientists. If they pull this off, the lack of U.S. funds could cripple both climate bodies. 

That’s just the beginning. A Republican majority likely means Senator James Inhofe, the Senate’s best-known climate change denier, will become the chair of the Environment and Public Works Committee. Inhofe would like to see EPA funding gutted and thinks climate change science is a hoax. Even if President Obama vetoes Republican anti-EPA legislation, Inhofe and other committee chairman can cause problems for the EPA through other means, like holding endless oversight hearings on the agency's proposals. 

Given how little time we have left to slash pollution and limit global warming, even minor setbacks could be major problems.