He also called it an "economic imperative." Everyone seems to understand that, except Republicans and their donors:

Obama, speaking a few miles from the site of the Nov. 13 terrorist attack in the French capital, called for urgent action against a challenge that he suggested was greater even than the fight against terrorism.

“The growing threat of climate change could define the contours of this century more dramatically than any other,” Obama said in a speech at the Le Bourget conference center in Paris’s industrial outskirts. “What should give us hope that this is a turning point, that this is the moment we finally determined we would save our planet.”

Obama, who has staked his legacy on the fight against climate change, struck an ominous tone in describing the ravages of a warming planet, declaring that “no nation large or small, wealthy or poor, is immune.” He urged the leaders to take action even if the benefits were not evident for generations.

Citing Martin Luther King Jr., he warned that “there is such a thing as being too late.”

The remarks came during a day of ceremonial fanfare as well as substantive progress in marshaling resources to speed the shift to cleaner energy. U.S. officials formally announced the formation of a 20-nation initiative to spur funding on energy research, in tandem with a similar undertaking led by Microsoft co-founder Bill Gates and 27 of the world’s wealthiest private investors.

But there were also signs of discord as negotiators prepared to haggle over details of a complex treaty that requires all nations — even the poorest ones — to make a contribution to cutting greeenhouse-gas pollution. Some developing countries have insisted on compensation for economic and environmental damage stemming from decades of industrial emissions that came mostly from Western industrial powers.