The US will double its climate aid for poor countries to at least $860 million (£559m).
The fund will help the most vulnerable countries help tackle climate change.
An additional fund worth $3 billion (£1.95bn) will help those nations move to green energy and cut emissions.
Mr Kerry said: “We are prepared to do our part and we will not leave the most vulnerable nations among us to, quite literally, weather the storm alone.
“Now, protecting our future before it’s too late will depend on whether all of us – every nation – is prepared to meet this moment.”
The UN also launched an initiative to build climate resilience in the most vulnerable countries.