Climate Accord Is a Healing Step, if Not a Cure

LE BOURGET, France — After the stomping and cheering died down, and the hugs and toasts ended, a question hung in the air as the climate conference came to a close: What does the new deal really mean for the future of the Earth?

Scientists who closely monitored the talks here said it was not the agreement that humanity really needed. By itself, it will not save the planet.

The great ice sheets remain imperiled, the oceans are still rising, forests and reefs are under stress, people are dying by tens of thousands in heat waves and floods, and the agriculture system that feeds seven billion human beings is still at risk.

And yet 50 years after the first warning about global warming was put on the desk of an American president, and quickly forgotten, the political system of the world is finally responding in a way that scientists see as commensurate with the scale of the threat.

“I think this Paris outcome is going to change the world,” said Christopher B. Field, a leading American climate scientist. “We didn’t solve the problem, but we laid the foundation.”

The agreement reached here on Saturday will, if faithfully carried out, achieve far larger cuts in emissions than any previous climate accord. It will reduce, without eliminating, the risk that runaway climate change might render parts of the Earth uninhabitable. It will lessen somewhat the possibility of a collapse of one of the ice sheets, which would cause a rise in the sea of 20 feet or more.

The deal, in short, begins to move the countries of the world in a shared direction that is potentially compatible with maintaining a livable planet over the long term.

Hans Joachim Schellnhuber — a pioneering environmental scientist, chairman of the German government’s advisory committee on climate change, and climate adviser to Pope Francis — declared on Saturday that “this is a turning point in the human enterprise, where the great transformation towards sustainability begins.”

Perhaps the most important part of the deal is that it explicitly recognizes that countries were not ambitious enough in the emissions cuts they pledged ahead of the Paris negotiations, pledges that were incorporated into the document. The agreement, in effect, criticizes itself for not doing enough.

To compensate, the deal sets up a schedule of regular review that will encourage countries to raise their goals over time. It envisions a tighter system to monitor whether the nations are keeping their promises — though how tough that will really be was put off to future debates.

In interviews, scientists with long experience studying climate change, and a long history of being discouraged by the politics of the issue, said they were heartened by the cooperative tone in Paris.

But for the deal to mean anything, they said, the celebratory moment must give way immediately to an era in which intensive efforts are made to squeeze emissions out of the world economy. That task will fall largely to businesses and investors, operating under emissions-reduction policies that countries have pledged to put into effect by 2020.

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