(Editor’s Note: Earthjustice attorneys Martin Wagner and Erika Rosenthal are blogging from the United Nations climate conference in Cancun, Mexico.)

Just before midnight last night at a stock-taking session here at the climate negotiations, applause broke out for the first time in a tense day. The Swedish delegate spoke not in the rarefied jargon of these talks, but from the heart as though talking to friends and family. He urged compromise and spoke of it as the key ingredient to a functioning family, country and, indeed, international community—especially when faced with the greatest challenge in history.

Compromise is a heavy lift in these negotiations, as it has been in efforts at home (in the U.S.) to pass a climate bill. But without it, the heavy toll climate change is already exacting in human lives, wildlife and ecosystems—witness this year’s devastating floods in Pakistan, landslides in China and wildfires in Russia—will only increase.

At the heart of it all is compromise on how developed and developing nations will share the effort of reducing global greenhouse gas emissions.

Developed countries became rich by burning fossil fuels, and polluting and warming the atmosphere. Because of these historical emissions, nations agreed in the 1992 climate treaty that rich countries would take the lead in reducing emissions while helping low-income countries to move toward a sustainable, clean energy development path.

Now, almost 20 years later, although China has surpassed the U.S. as the largest annual GHG emitter, the average emissions of each individual American is five times more than a person in China, and 20 times more than a person in India. Despite this disparity, China has pledged to drastically slow the growth in its emissions over coming years.

What we can’t compromise on though, is the level of ambition. According to a report from scientists convened by the United Nations Environment Program, there is a major gap between what countries promised to do in last year’s Copenhagen Accord and what is necessary to have even a decent chance of avoiding irreversible, dangerous global warming. This gap has become known in the gigatonne gap.

No matter what happens today and into the wee hours of tomorrow morning here in Cancun, countries must agree to strengthen their pledges in the future and identify a path to close the gigatonne gap. This much, at least, Cancun can and must deliver.

In the U.S. we can all contribute to this critical, bottom line goal by redoubling our efforts to ensure that the US delivers on its Copenhagen Accord pledge—a 17 percent emissions reduction below 2005 levels. Even with the failure of climate legislation in the Congress, our landmark environmental law, the Clean Air Act, can get us there.