Perhaps the most surprising story out of the Paris climate talks so far is the shift that seems to be occurring in favor of at least some acknowledgment — if not an outright embrace — of a 1.5 degrees Celsius global temperature target in a final agreement here.

Holding warming to 1.5 degrees Celsius above pre-industrial levels — rather than to 2 degrees, which up until now has been the most widely accepted target – would be extraordinarily difficult if not outright impossible. Certainly, scientists have repeatedly suggested that to achieve such a powerfully ambitious target, with the world already at about 1 degree C and rising, one would need to overshoot 1.5 degrees and then come back down again using problematic “negative emissions” technologies.

So then why would the idea be coming on so strong right now?

Perhaps the most surprising story out of the Paris climate talks so far is the shift in favor of… a 1.5 degrees Celsius global temperature target in a final agreement here.

The simple answer is that while the advocacy of small island nations on behalf of the 1.5 C goal has clearly been quite influential, in some ways just as persuasive has been, you know, science — particularly when it comes to the issue of sea level rise.

“The combination of small island states and the sea level commitment stuff is the big ball and hammer that has been taken out now,” says Anders Levermann, a researcher with the Potsdam Institute for Climate Impact Research who spoke here at the conference about the latest research on sea level rise and the planet’s ice sheets. “It’s saying, this is a moral imperative, we cannot rid people of their countries.”