Protests in Washington that disrupted the morning commute tried to drive home the urgency for change.

Most quoted: The teenage activist Greta Thunberg lit into the gathered crowd for their “business as usual” approach. “We are in the beginning of a mass extinction and all you can talk about is money and fairy tales of eternal economic growth,” she said, visibly angry. “How dare you.” Watch the video.

Major emitters: China, the largest greenhouse gas emitter, signaled no ambition higher than the targets in the Paris Agreement. India said it would increase its share of renewable energy by 2022 but made no promises to reduce its use of coal. The most notable pledges came from cities and private businesses.

President Trump unexpectedly dropped into the hall, but made no address. The former New York City mayor and billionaire Michael Bloomberg drew some laughter when he told Mr. Trump, “Hopefully our discussions here will be useful for you when you formulate climate policy.”