L'AQUILA, Italy — President Barack Obama and his G-8 summit partners wrestled anew with global warming amid tense discussions Thursday about how rich and emerging nations alike can live up to new clean-climate goals adopted by leading industrialized nations.

Nearing six months on the job, Obama has seen a flicker of progress: the chance for a new agreement among developed and developing nations to cap rising global temperatures, plus goodwill from his peers for repositioning the U.S. as an aggressive player in the debate.

Yet when Obama thrusts himself foursquare into this discussion, he will run smack into the same old problem: Neither the wealthy nor the countries in search of their own footing think the other side is doing enough. And only when the pollution emitters work together on a binding plan will a climate strategy work, experts say.

Even victory came with a setback on Wednesday. The Group of Eight set a goal of cutting all greenhouse gas emissions in half by 2050, but developing nations refused to go along.

Confronting global warming — a trend scientists say could unleash devastating droughts, floods and disease if left unchecked — is a dominant theme again at this year's G-8 summit of Britain, Canada, France, Germany, Italy, Japan, Russia and the United States.

U.N. Secretary-General Ban Ki-Moon said today the G-8 countries must come forward with financing for poorer nations to change their carbon-heavy growth patterns and adapt to the effects of global warming. He said the G-8 must do both if developing countries are to cut their own emissions.

The G-8 on Wednesday recognized for the first time that average global temperatures shouldn't exceed 2 degrees Celsius from preindustrial times. But the leaders made no commitments to do anything in the near-term to reach that goal and they made no firm financial or technological commitments for poor countries.

In another development, a draft declaration obtained by The Associated Press shows that leaders assembled here want to resume stalled trade talks by 2010 and head off protectionist policies — a position that Obama has embraced. Completing the so-called Doha round has risen up the agenda due to fears that the economic crisis will lead to an upsurge in protectionist policies like the ones that helped cause the Great Depression of the 1930s.

Obama was taking part in discussions all day on climate and a host of economic issues, and the number of countries represented at the table will just keep growing.

First, the traditional industrialized powers will expand their forum to other strategic economies: Brazil, China, India, Mexico and South Africa, plus a special invitee, Egypt.

And Obama later will help lead a forum of major economies that also includes Australia, Indonesia and South Korea. Together, including the U.S., the represented countries account for about 80 percent of the emissions of the heat-trapping gases blamed for global warming.

The results this week will be a pivotal marker of what could happen in talks in December in Copenhagen, when the United Nations tries to conclude a new worldwide climate deal.

The two blocs — the richest countries and the fastest growing ones — did strike an important agreement Wednesday. Their unified position now is that global temperature should be kept from rising by more than2 degrees Celsius.

That's the point at which the Earth's climate system would fall into perilous instability, according to the United Nations' chief panel on climate change.

The U.S. and the other G-8 nations set a new goal of reducing their greenhouse gas emissions by 80 percent or more by 2050, part of their global goal of a 50 percent cut.

But the emerging countries are refusing to commit to specific reduction targets.

They are upset that the industrialized G-8 has not been forthcoming on either midterm emissions reductions — well before 2050 — or pledges of financing and transferring technology to the developing world. And they worry that major reductions could hamper their economies.