Use the timeline below to see the evolution of today's top 20 CO2-emitting countries, based on their total and per capita emissions:

For 10 days in December 1997, a swarm of scientists, diplomats, presidents and prime ministers met in Kyoto, Japan, to sketch out humanity's first unified game plan for fighting climate change. Next month, as the resulting treaty nears its expiration date and greenhouse gas emissions continue to rise worldwide, the planet's leading climate negotiators will reconvene in Copenhagen in hopes of retooling and rerunning that game plan. This time, however, they want all the players on the field.

The Kyoto and Copenhagen summits are both part of the broader U.N. Framework Convention on Climate Change, a treaty that emerged from Rio de Janeiro's 1992 Earth Summit and set the stage for all U.N. climate talks that followed. Rather than trying to get all 150 countries to agree on new regulations at the time, the UNFCCC called for future "protocols" to establish mandatory emissions cuts for carbon dioxide and other greenhouse gases. The countries agreed to hold annual "Conferences of the Parties" starting in 1995, with the goal of drafting a protocol that would cut emissions while dodging an economic backlash.

The Kyoto Protocol was born in 1997 at the third Conference of the Parties (known as COP3), but it lost much of its punch when the United States — the world's No. 1 emitter of carbon dioxide at the time — refused to ratify it. Many U.S. senators, and later President George W. Bush, criticized the Kyoto Protocol for placing mandatory emissions cuts on industrialized nations while essentially giving a pass to the developing world. Citing fears of losing an economic edge to China or India, the United States opted out of the treaty, leaving the country exempt from its emissions rules.

The issue of when and how much various countries should reduce their emissions has remained a thorn in the side of climate negotiators ever since. The Kyoto Protocol languished without heavy emitters like China and the United States, and even some participating countries have failed to meet their Kyoto targets. From 1998's COP4 in Buenos Aires to 2008's COP14 in Poznan, Poland, negotiators have nonetheless pushed ahead in their efforts to galvanize the world against global warming, and this year — at December's COP15 summit in Copenhagen — they may have their best chance yet.

Copenhagen wind farmHopes hang on Copenhagen

COP15 will be dedicated to drafting a replacement for the Kyoto Protocol, which starts expiring in 2012. Political climates have changed considerably since 1997, but getting nearly 200 countries to agree still won't be easy. China is now the world's top CO2-emitting nation, with India gaining on the No. 3 spot, and while both countries have begun embracing more renewable energy sources, their CO2 emissions are still rising. Both also still oppose mandatory emissions cuts, which they argue should be shouldered by the industrialized countries that spent the 20th century freely emitting much of the CO2 that now clogs the atmosphere.

The United States has grown more climate-conscious in recent years, and President Barack Obama even said this week that he would attend the COP15 summit in Copenhagen if his appearance could help get a treaty approved. But the country's domestic cap-and-trade climate bill — demanded by many in the international community as a good-faith measure to prove America's commitment — is now stuck in the Senate and unlikely to receive a floor vote before December. And while China has passed the United States as the top overall emitter, the U.S. per capita rate is 19.85 metric tons of CO2 per person annually, the highest of any developed country on Earth.

The outlook for Copenhagen remains hazy just a few weeks before the conference begins, clouded by a flurry of moving parts and competing agendas. International negotiators met in Barcelona earlier this month in a last-minute effort to drum up support for a new treaty, and U.N. Secretary-General Ban Ki-moon visited Washington, D.C., this week to make sure the United States is still on board. But, as with any game plan, such preparation can only go so far — the true test will come when the Copenhagen summit kicks off on Dec. 7.

See the infographic above for an in-depth rundown of which countries have emitted the most CO2 since 1950, and how their emissions have evolved over time. The top 20 emitters are ranked in two categories, total emissions and per capita emissions, based on data from the U.S. Carbon Dioxide Information Analysis Center, the U.S. Energy Information Administration, the U.S. Census Bureau and the United Nations Statistics Division. (The countries listed are the top 20 in each category from 2006, the most recent year for which global data are available.)

For more background on climate change and climate negotiations, check out the links below. And stay tuned to MNN for the next installment of our weekly "Road to Copenhagen" series leading up to the conference's opening day.

Photo (Old Stock Exchange in central Copenhagen): U.S. Department of Commerce

Photo (offshore wind farm outside Copenhagen): Tariq Mikkel Khan/AP/POLFOTO

MNN homepage photo: BenGoode/iStockPhoto

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