There were notable pledges of action, but several important greenhouse gas polluters were conspicuously silent. It showed the challenges that lie ahead.

Much remains unresolved barely three months into a presidency that has vowed to make climate change a centerpiece of its foreign policy. Many important capitals dont yet have a United States ambassador in place, let alone diplomats versed in the science and economics of climate policy.
The administration needs the approval of Congress to mobilize money for its domestic climate goals and for overseas development aid that its promised. There is no political appetite, especially among Republicans, for a carbon tax. And Mr. Kerry has said he is concerned about a carbon border tax that the European Union is poised to establish on imports that come from countries that do not impose levies on goods that depend heavily on fossil fuels.
The administrations next test of climate diplomacy comes when Mr. Biden travels to Britain and Belgium in June for the next Group of 7 meeting, his first overseas trip as president. That is all the more crucial if it expects to move China along.
Relations between Washington and Beijing are at their lowest in decades, and even on the issue of climate change, there have been tense exchanges of words. The Chinese Foreign Ministry spokesman last week described the re-entry of the United States into the Paris climate agreement as a truant getting back to class.
Mr. Kerry said on Friday that the comment was not particularly conducive to a conversation on climate action, and that he had told his Chinese counterparts just that.
Key to any American strategy, analysts said, is breaking out of the isolation of the last four years, which makes the next few months extremely important. If the United States wants to have significant leverage with China it will have to work with allies, Ms. Hillman of the Council on Foreign Relations said.
Lisa Friedman contributed reporting.