In 1997, more than 150 countries came together in Kyoto, Japan, to negotiate a deal to reduce the greenhouse gas emissions driving global warming. Back then, the negotiations centered around developed countries, like the U.S., Japan and Australia with the intention that richer countries would lead the way and create a legally binding treaty with emissions targets and reduction timelines.

Eighteen years later, the world is still trying to agree on how to tackle climate change. But this time around, the U.S. pledge does not require congressional approval. That approach echoes an important lesson from Kyoto: A treaty’s worth is directly tied to the president’s ability to enact it.

In Kyoto, one of the U.S.’s top priorities was to establish a structure and market for limiting and trading emissions. Elliot Diringer, who attended the Kyoto talks as communications director for the Clinton administration’s White House Council on Environmental Quality, told me recently that emissions trading had proved very effective for tackling acid rain and that American negotiators considered that problem a good model to apply to greenhouse gases.

But the agreement never went into effect in the U.S. After Kyoto, where Al Gore, then the vice president, spoke of setting “binding emissions limits,” the Clinton administration returned home to a Congress that refused to take part in the treaty. Before the conference, the GOP-controlled Senate passed the Byrd-Hagel resolution in a 95 to 0 vote; it resolved that the United States should not be a signatory to any protocol that mandated the reduction of greenhouse gas emissions unless it also required reductions from developing countries during the same time period. That meant Clinton never got the Kyoto Protocol ratified, and George W. Bush never tried. The U.S.’s abandonment of the treaty didn’t kill it, but it severely limited its effectiveness.

The lesson of Kyoto was stark. “We learned the limits of what the U.S. can agree to,” said Rafe Pomerance, who went to Kyoto as deputy assistant secretary of state for environment and development. “Climate change policy is not fully dictated by negotiations,” he said. “They’re dictated by domestic political opportunities and constraints.” President Obama can pledge only what he can achieve through executive action, and that means that the agreement has to be a non-binding commitment that does not require congressional approval. “If the U.S. Congress won’t move, the U.S. is heavily constrained and therefore the world is constrained,” Pomerance said. Whether or not the U.S. is the largest emitter (China overtook the U.S. as the world’s biggest emitter in 2007), it’s still a major actor.

So the Paris negotiations have taken an alternative tactic. At Kyoto, actual targets were hashed out at negotiations run by Argentinian Ambassador Raul Estrada-Oyuela, who famously insisted on keeping the talks moving forward and even physically stopped the clocks at one point to ensure that a deal was struck. This time, the meeting is taking a bottom-up approach. Rather than negotiating their targets in Paris, countries submitted their pledges ahead of time, and there’s little expectation that these pledges will be negotiated further, as they were in Kyoto. (The U.S. arrived in Kyoto with a proposal to reduce greenhouse gas emissions to 1990 levels but left having agreed to reduce them to 7 percent below 1990 levels.)

The Paris approach is less ambitious, but it’s probably more realistic. The pledge that his administration submitted to the climate conference — to reduce emissions by 26 percent to 28 percent below 2005 levels by 2025 — relies on actions administered through the Environmental Protection Agency and Department of Energy, which gets around the need for congressional ratification. Republican members of Congress are already fighting these measures, and if a Republican takes the White House, the administrative actions could be undone.

While politicians talk about what to do, greenhouse gas emissions continue to rise. Since the Kyoto Protocol was negotiated, the number of weather and climate disasters worldwide has risen 42 percent, and the seas have risen nearly 6.2 centimeters, on average.