these pledges be enough to ward off the worst consequences of global warming? No. Scientists generally agree that global warming must not exceed 2 degrees Celsius, or 3.6 degrees Fahrenheit, from preindustrial levels. Various studies say that even if countries that have made pledges were to follow through on them, the world will heat up by 6.3 degrees Fahrenheit by the end of this century. That would still be much too high, and it would be guaranteed to make life miserable for future generations, especially in poor low-lying countries. But it would at least put the world on a safer trajectory; under most business-as-usual models, temperature increases could reach 8.1 degrees or higher.
Eventually, of course, all nations will have to improve on their pledges, especially big emitters like China, India and the United States. If the Paris meeting is to be a genuine turning point, negotiators must make sure that the national pledges are the floor, not the ceiling of ambition, by establishing a framework requiring stronger climate commitments at regular intervals — say, every five years. This should be accompanied by a plan for monitoring and reporting each country’s performance. Earlier meetings have done poorly on this score.
Other important items dot the agenda. One is how rich nations can help poorer ones achieve their targets. Another is stopping the destruction of tropical forests, which play a huge role in storing carbon and absorbing emissions. The meeting also seeks to enlist investors, corporations, states and cities in the cause. Michael Bloomberg, who made reducing emissions a priority as mayor of New York, will join the mayor of Paris in co-hosting a gathering of local officials from around the world.
The test of success for this much-anticipated summit meeting is whether it produces not only stronger commitments but also a shared sense of urgency at all levels to meet them.