Pointing to a summer of record heat and extreme weather in which London was improbably hot and dry, while New York was unexpectedly rainy, Mayors Sadiq Khan and Bill de Blasio are calling on cities around the world to join them in divesting their shares in fossil fuel companies and join a new global initiative on finance and investment.

“As mayors, we are not only committed to taking bold action to tackle climate change and to improve the lives of those we represent, but also to showing others the way,” they write, in a joint opinion piece for The Guardian. “London and New York are two of the world’s most dynamic, innovative, and forward-thinking cities, and we are determined to push ahead with the goals of the Paris Agreement—stealing a march on many national governments.”

But to make that happen, “we must also use our economic might to accelerate the transition to a low-carbon economy,” they add. “Ending institutional investment in companies that extract fossil fuels and contribute directly to climate change can help send a very powerful message that renewables and low-carbon options are the future,” while fostering sustainable investment to fund “the scale of transformation the world needs”.

Both cities have already begun divesting their fossil assets, de Blasio and Khan report: the London Pension Fund Authority’s fossil investments are down below 2% of its total portfolio, while New York is committed to dumping US$5 billion in fossil stocks in the next five years. And they say both cities are investing in a sustainable future: London with a £500-million Mayor’s Energy Efficiency Fund, New York with $2.7 billion in energy efficiency programs, a six-fold increase in solar capacity since 2016, and more than 1,200 city-owned electric vehicles, with 500 charging stations.

“Of course, we acknowledge that divestment and accelerating green investment is not always straightforward,” they write. “The major portfolios held by public entities are typically pension funds, which aren’t generally under the control of mayors. But we can make progress if we work together with a range of partners—including pension funds, local authorities, campaign groups, and the private sector.”

Along the way, cities “can send a clear message to the fossil fuel industry: change your ways now and join us in tackling climate change.”