Greenhouse gas emissions cuts by cities could fill a quarter of the "gap" between carbon reductions pledged by countries and the action that is needed to prevent dangerous climate change, a city leaders group has said.
At the Climate Summit for Local Leaders event in Paris, where crucial UN talks on tackling climate change are being held, the "C40" group said commitments already made by cities would deliver half of the world's potential urban emissions reductions by 2020.
Pledges made by countries in the run up to the UN climate talks for the action they would take to curb emissions do not get the world on track for limiting temperature rises to 2C above pre-industrial levels - beyond which dangerous climate change is expected.
But the C40 group of major world cities leading action on greenhouse gas emissions said total potential urban emissions reductions in 2030 could close the "gap" by nearly 25% between what had been pledged and the 2C pathway.
They also announced a project - launched with £3.8 million - which it is hoped will unlock up to 1 billion US dollars (£660 million) for green infrastructure projects in cities in developing countries.
City and regional leaders are meeting in Paris to discuss how they can tackle climate change, and UN secretary general special envoy on cities and climate change Michael Bloomberg, the former mayor of New York, told C40 leaders the work they did was "essential".
He told world leaders attending the start of the UN talks in Paris, which aim to hammer out a new deal to curb temperature rises to no more than 2C, that they had a much better outlook for a deal than during the previous, failed, bid for a global climate agreement in Copenhagen in 2009.
"Much of that comes from the progress made by cities," he said.
"Whatever agreements the national leaders make, the execution takes place in the cities led by mayors.
"A lot of people are sceptical about what we do, a lot of people don't like it when we effect change, but the bottom line is, if we don't do this, the world is in a very precarious position," he said.
Speaking on a panel at the event, London Mayor Boris Johnson pointed to how collaboration between cities to buy low carbon, electric or hybrid buses had driven down prices by 10% in just a few months.