Updated

U.S. Secretary of State John Kerry announced Wednesday that the United States will double its contribution to helping vulnerable nations adapt to climate change impacts, as he appealed for the world to take action to deal with the phenomenon.

Challenging participants at U.N. talks here to reach a new global climate agreement by Friday's self-imposed deadline, Kerry said the U.S. would increase the amount of money it provides for climate adaption grants to $860 million from $430 million by 2020. Developing nations have been demanding more money for adaption as they struggle with increased extreme weather events, like hurricanes, heavy rains and floods.

The money will be part of an existing promise by wealthy countries to jointly mobilize $100 billion a year by 2020 in climate finance. It will help fund domestic weather services and tracking systems to better assist poorer nations in forecasting and coping with extreme weather.

Kerry made the announcement in a speech to the climate conference outside Paris.

In it, he noted the increasing damage from increasingly frequent severe weather, such as the recent flooding in Chennai, India, and smog in China's capital. Along with other events, "they are warning signs that no rational person should ignore," Kerry said, adding that the meeting "may well be the best chance we have to correct the course our planet is on."

"If we just continue down our current path, with too many people sitting on their hands and waiting for someone else to take responsibility, the damage is going to increase exponentially," Kerry said. "To cut to the chase: Unless the global community takes bold steps now to transition away from a high-carbon economy, we are facing unthinkable harm to our habitat, our infrastructure, our food production, our water supplies, and potentially to life itself."

"The situation demands, and this moment demands, that we do not leave Paris without an ambitious, inclusive, and durable global climate agreement," he said.

A draft agreement is to be prepared Wednesday afternoon, reflecting the progress made so far, that will leave two days for foreign and environment ministers to work out the most difficult issues, like how to spell out who should do what.

In his speech, Kerry, who has made combatting climate change a priority project since he became secretary of state, sounded familiar themes. He mocked climate change deniers and expressed optimism that private sector energy innovations would skyrocket after an agreement was reached.

Kerry said deniers are "so out of touch with science that they believe rising sea levels don't matter, because in their view, the extra water will just spill over the sides of a flat Earth." On technology, he said agreement in Paris would send "the marketplace an extraordinary signal" of commitment to clean energy and thereby spark a flood of capital into the sector.

He also cast his argument in broader terms, maintaining that climate change is literally a life and death issue for some nations now and will soon be for more.

"Make no mistake: If, as a global community, we refuse to rise to this challenge — if we continue to allow calculated obstruction to derail the urgency of this moment — we will be liable for a collective moral failure of historic consequence," he said. "We are not just responsible to ourselves — we are responsible to the future."