The rhetoric soared today as rich nation leaders — UK Prime Minister Gordon Brown, Australia’s PM Kevin Rudd and Secretary of State Hilary Clinton — urged completion of a deal to slow global warming.

The mood in Copenhagen had been growing ever gloomier following the revelation on Wednesday of a ‘text from the sky’ by Danish Prime Minister Lars Rassmussen, as the Chinese negotiator Su Wei described it. The heavy snow flurry added to the chill among delegates about the prospects of any deal being struck this week.

But today the United States emerged with a proposal that lifted the atmosphere inside the Bella Centre in the Danish capital. News that the U.S. was committed to finance for developing nations of $100 billion per annum by 2020 was a breakthrough, despite its dependence on large developing nations accepting United Nations verification of their own targets to cut greenhouse gas emission intensity.

It was a day of engagement by political leaders at the final stretch of these two years of negotiations. French president Nicolas Sarkozy, in a fiery Gallic tone, named China several times and attacked the developing nation for its failure to embrace a transparent process. Yet for those of us who have been wary of the potential for a trade-off between efforts to reduce global poverty and investing in a safer climate, Mr. Brown’s words were inspirational, noting that money for climate change programs ought not be siphoned from existing overseas aid commitments:

And to address the gaping sorrows of the left-out millions in Africa, the torment of our island states, the fear gripping the planet’s most vulnerable communities, and the urgent need to reduce rates of deforestation, we must commit to additionality in our support so that we do not force a choice between meeting the needs of the planet and meeting the millennium development goals.

The parties have progressed today, and a small hope appears reborn, although the world is still a long way from a successful, ambitious agreement.

It remains up to the leaders, with the weight falling especially heavily on the shoulders of President Obama. He will not want to walk away from Copenhagen for the second time this year with empty hands. We pray his ability to reach across political chasms, bridging cultures from Kenya to Kansas, will nudge the process enough, building the case for a unprecedented action as a global community even in these final hours.

Tim Costello is CEO of World Vision Australia.