The Copenhagen conference on climate change opens against an ominous backdrop. Global greenhouse gas emissions and temperatures are rising at an alarming and unanticipated pace. The impacts of climate change are now readily apparent, with temperatures climbing, Arctic sea ice disappearing, and sea levels already rising at rates beyond even the worst-case estimates of the Intergovernmental Panel on Climate Change. Scientists are telling us that global greenhouse gas emissions must peak within the next decade, and decline steeply thereafter, if the world is to have even a chance of avoiding catastrophic climate change.

In Copenhagen, however, expectations have been low. Many believe that the stage is set largely for further international disagreement and inaction, largely because the United States has been unable—or, more accurately, unwilling—to commit to reducing its own greenhouse gas emissions.

After a long period of deliberation on how to approach an international agreement, President Obama has finally announced plans to attend part of the Copenhagen conference. He also has offered an emissions reduction target for the United States. His target, however, falls far short of the reductions scientists believe are necessary to avoid catastrophic consequences.

The President apparently believes that he cannot act on the international stage without a green light from Congress, and cannot propose any measures stronger than those Congress might one day approve. The most common excuse for this view is that any agreement in Copenhagen would have to be in the form of a treaty, which under U.S. law must be ratified by two-thirds of the Senate to take effect.

But this view is incorrect as a matter of law. The U.S. Supreme Court has repeatedly held that the President has legal authority to bind the country internationally, by way of an “executive agreement,” without submitting a treaty to the Senate for supermajority approval. In fact, Congress already has given the President specific authority to negotiate international agreements to reduce greenhouse gas emissions. The President also could make an international commitment grounded in his power—and indeed, his duty—to enforce existing U.S. environmental laws. Powerful and effective statutes like the Clean Air Act, Clean Water Act, Endangered Species Act, and National Environmental Policy Act provide ample and readily available tools for addressing America’s contributions to the climate crisis. These laws could be implemented more quickly, and with far greater scientific credibility, than any compromise “cap-and-trade” system that Congress might (or might not) someday enact. All President Obama has to do is promise the international community that he will use his power as the Chief Executive to enforce existing laws in a manner that effectively reduces the country’s greenhouse gas emissions.

In short, any one of these sources of authority would allow President Obama to make a binding, meaningful commitment to the international community. Together, these congressional enactments and environmental statutes give President Obama a very strong hand—strong enough to do what the science demands, and not just what a divided and rancorous Congress might someday allow.

Can President Obama contribute meaningfully to a global solution in Copenhagen? As this paper demonstrates, the answer is clearly, “yes, he can.” It only remains to be seen whether he will.