Leaders from the world's most influential nations will gather this June in Toronto, where they will take the next steps toward developing global solutions to climate change. These countries -- the United States, China, India, Brazil, the members of the European Union, and the 15 other members of the so-called G20 -- hold the keys to curbing the greenhouse gases that are warming the planet. They account for two-thirds of the world's population, 85 percent of global economic output, and a comparable level of worldwide carbon emissions.

The G20 summit can be a useful complement to the U.N. climate talks in Copenhagen last December. It's a forum for the countries that have contributed most to the problem, explains Jacob Scherr, director of international programs for NRDC, who has represented the organization at global environmental talks since the Rio de Janeiro Earth Summit in 1992. "It's nice to have an agreement among 192 countries," he says, "but the future of the planet will be decided by about 10 countries that have most of the world's population and are responsible for most of the world's pollution."

Of course, big, sprawling U.N. meetings are still vital, because they bring all countries to the table, rich and poor alike. This is especially crucial in designing aid and assistance strategies that can help developing countries cope with and adapt to climate change. That's why negotiators will meet in Cancun, Mexico, in late November to pick up where Copenhagen left off. Some observers were disappointed when those talks failed to produce a binding accord, but there was genuine progress: major carbon emitters pledged cuts and agreed to make public their progress and assist poor countries. Unfortunately, U.N. Secretary-General Ban Ki-moon had spent months raising expectations that negotiators would seal the deal in Copenhagen, when in fact not all nations were ready to deal.

Still, the United Nations is hardly to blame. The sheer diversity of national interests, economies, and political systems represented at U.N. talks virtually guarantees policy paralysis on a subject as complex as climate change, says former U.S. negotiator Adele Morris, who dealt with land-use and forest issues during U.N. climate talks a decade ago in The Hague, Netherlands. "If you need a treaty that involves heavy-duty political compromise, that is not how it happens," says Morris, policy director for climate and energy economics at the Brookings Institution.

Far from a diplomatic free-for-all, the annual G20 summit follows a tightly scripted agenda that builds on goals laid out in previous sessions. Aides from each country's diplomatic, economic, and financial policy corps meet regularly in the months between summits, working to hone agendas and discussion topics. When President Obama hosted his G20 counterparts last fall, for instance, they agreed to phase out subsidies for oil, coal, and gas. Sure enough, when Obama sent Congress his 2011 budget proposal earlier this year, it included substantial cuts in those subsidies.

When they meet again in June, the G20 leaders will report on progress they've made on their pledges to invest in renewable energy, to exchange clean energy technology, to engage in joint research, and to provide financial support to help developing countries cope with the impacts of climate change.

But one important piece of the puzzle is still missing. To demonstrate true global leadership, it is widely acknowledged here and abroad, the United States must pass clean energy and climate legislation at home. Getting a consensus among a majority of U.S. senators (the House of Representatives already passed climate legislation last year) has sometimes seemed as challenging as brokering a treaty among the world's 192 nations. But the long wait for domestic climate legislation may soon be over: a bill was finally circulated in the Senate in May, and if it passes, we could be witness to a new phase of international cooperation and action.