A climate of fear in Paris will not keep those fearful of climate change from gathering in the French capital for Monday’s start of a United Nations conference on our warming planet. That’s a good signal on several fronts. It’s a deserved display of unity as Parisians still reel from recent terror attacks, and it shows the world that the city can be secured for world leaders, let alone everyday residents and tourists.

Most important, it reflects that even in a turbulent world in which conflict creates multiple crises on multiple continents, climate change cannot be ignored as a grave global threat that demands action now in order to avoid catastrophe later. That’s not just the view of a vast majority of scientists, but also many economists, ever more businesses and especially the Pentagon, which along with most militaries in allied NATO nations considers potential disruptions from climate change to be a growing threat. Indeed, the current migration crisis upending the Mideast, North Africa and Europe may look manageable compared to the global dislocation possible from unchecked climate change.

There could be “severe consequences,” Kare Aas, Norway’s ambassador to the U.S., told an editorial writer after a Nov. 24 speech in Minneapolis to the Norwegian American Chamber of Commerce on “Climate and Arctic — the Way Forward.” Challenges from climate change could go well beyond the impact on the Arctic, Aas said. Beyond security and migration, he said possible disruptions in fishing pose a threat for the food supply.

A different kind of waterway — rivers — is the focus of St. Paul Mayor Chris Coleman, who will attend the Paris conference. Coleman, co-chairman of the Mississippi River Cities and Towns Initiative, said he is working with mayors from other river basins to highlight how climate change could impact drinking water, transportation and other river issues.

“You hear a lot about what happens with rising sea levels,” Coleman told an editorial writer. “But when you think about the Mississippi River alone, 20 million draw their drinking water out of the river every day.” Some rivers are threatened by climate-change rainfall disruptions, and while some river levels may fall, others face more rain — and thus more runoff and pollution. Cities, too, can do more, Coleman said, to take “measurable, and measured, responses to climate change.”

But beyond cities, countries must mitigate the threat. As with nearly every global issue, the U.S. will be looked to for leadership. President Obama has already acted on many fronts. But to be most effective he needs Congress, and many legislators, most of them Republicans, have pledged to thwart his ambitions. The U.S. stands alone as a Western nation with such a partisan split on climate change. Republicans should heed the science and offer policy alternatives if they disagree with Obama. But denial isn’t conservative, it’s reckless.

As for the rest of the world, implementation of commitments that emerge from the conference matters most. “Paris is a step forward, but not the end,” Aas said.