UNITED NATIONS – It happened in Rio, in 1992: The world officially woke up to the fact it was getting warmer outside. Seventeen years later in New York, the U.N. gathered presidents and premiers to talk about serious steps to turn down the heat. But the political climate may still be too cool for conclusive action.

In inviting President Barack Obama and other world leaders to Tuesday's summit on climate change, Secretary-General Ban Ki-moon urged them to "act as global leaders rather than national leaders," to push climate negotiations forward.

With a mere 76 days to go before a pivotal diplomatic conference, it appeared an interim agreement might be the most that can be expected this December, leaving difficult details for later talks.

Ban's bid to build momentum for a new climate accord was the latest effort in a long, cumbersome process dating back to the 1992 Earth Summit in Rio de Janeiro.

Leaders converging on the Brazilian city signed on to something unprecedented, a treaty committing them to work "to protect the climate system for present and future generations."

Scientists had produced persuasive evidence the carbon dioxide, methane and other greenhouse gases that industry, transport and farming were pouring into the atmosphere were trapping heat and raising global temperatures, with potentially damaging effects — droughts, floods, rising sea levels — from a changing climate.

Then-President George H.W. Bush called on fellow summiteers to "join in a prompt start on the convention's implementation."

Not promptly, but five years later the world's nations agreed to add the Kyoto Protocol to the treaty, with its first, modest reductions in emissions by industrialized countries.

The U.S. Senate repudiated the pact, however, and the process entered an eight-year slowdown as a second Bush administration, of President George W., resisted global pressure for deeper concerted action.

The U.S. opponents complained emissions reductions would crimp the American economy, and objected to Kyoto's excusing of China, India and other poorer countries from having to reduce their energy use.

As the diplomacy decelerated, climate change accelerated.

Average global temperatures had risen 0.74 degrees C (1 degree F) over the past century. Sea-level rise, from heat expansion and melting land ice, increased in the late 20th century.

Just last week, scientists reported that one of recorded history's greatest losses of Arctic sea ice to summer melt occurred this year, surpassed only by 2007 and 2008. Scientific forecasts are growing ever more bleak.

While waiting for change in Washington, diplomats in 2007 set a two-year timetable for replacing the Kyoto pact, which expires in 2012, aiming at a comprehensive deal at the annual U.N. climate conference this December in Copenhagen, Denmark. The election of Obama, who pledged U.S. action, put new life in the process. But time was working against success.

The House of Representatives did pass the first U.S. legislation to cap carbon emissions. The Senate, however, embroiled in the U.S. health care debate, delayed addressing the issue. Without U.S. domestic action, the rest of the world isn't likely to commit to an overall, detailed post-Kyoto accord.

"The negotiations are going far too slow. We are close to deadlock," Prime Minister Fredrik Reinfeldt of Sweden, which currently heads the European Union, acknowledged in the opening public session of Tuesday's summit. "As leaders we have a job to do. Our job is to break the deadlock."

But, as France's President Nicolas Sarkozy pointed out, "time is not our ally here." Time, in fact, was even in short supply on Tuesday, as some 100 national leaders and other envoys had a theoretical five minutes each to present their views in closed U.N. meetings.

It appeared increasingly that Copenhagen, at best, may produce a framework for further talks, while pieces fall into place in Washington and elsewhere, and Kyoto's formulas are perhaps extended.

Such a Copenhagen plan might set an aggregate goal for emissions reductions by richer countries, with 2020 and 2050 targets, and envision "policy-based" commitments by China and other poorer countries — for example, not reducing emissions directly, but reducing "carbon intensity," or fossil-fuel use per unit of economic growth.

Depending on how well the world is rebounding from the current economic slump, richer nations might also declare their readiness to boost financial support for developing countries to switch to clean energy technologies, and to adapt to climate change's impact on their crops, their shorelines and their economic lives.

At Tuesday's summit and earlier, China, India, Brazil and other developing nations indicated they're prepared to take such steps. The Europeans and Japan's new government, meanwhile, say they'll deepen their emissions cuts. And the Americans, 17 years after Rio, may be prepared to adopt their own reductions.

But December looks too close, and the issues too complex, for it to happen in Copenhagen in 2009.