When Pope Francis becomes the first pontiff to address a joint session of Congress this week, much focus will be on how Republicans will respond to the pope’s position on the climate. If Francis presses his case that the world must take urgent action to combat climate change, you can expect cameras to find Senate Majority Leader Mitch McConnell, whose office recently indicated it is doubling down on efforts to fight President Barack Obama’s new greenhouse-gas reductions.

But this domestic political drama, absorbing in its own right, may obscure a more important, even radical, shift in the global politics of climate change that Francis has helped to advance. In his June encyclical addressing the issue, he emphasized the fundamental environmental rights of the world’s impoverished, and suggested the rich who have benefited from fossil fuels have a moral obligation to help the poor who may suffer most from climate change. “The poor and the Earth are shouting,” the pope wrote.

Given the emerging science, many nations affected, the moral case pushed by the pope and the resistance of developed countries, there is strong reason to believe the grievance over funding for protection from climate impacts presents the most profound threat to a successful climate agreement.

This emphasis on the fate of the poor seems like an understandable moral position in keeping with Francis’ broader emphasis on poverty and inequality. But it also draws attention to one of the biggest practical hurdles currently standing in the way of the U.N. climate agreement being negotiated later this year in Paris.

Within those negotiations, the world’s least developed countries have become increasingly aggressive in pressing for some method of dealing with, and paying for, what they contend are growing climate change impacts affecting their coastlines, agriculture, fresh water supplies and more. In the language of climate talks, these are called “loss and damage” provisions—in which richer nations more directly compensate poorer ones for climate costs. These provisions have been proposed by developing nations in the U.N. negotiations for several years, but the major greenhouse gas emitters, including the U.S., the EU and China, have banded together to water them down.