London Mayor Sadiq Khan has joined leaders from 30 cities to call on governments to take urgent action to tackle climate change.

In an open letter to G20 leaders ahead of the summit in China, members of the C40 Cities Climate Leadership Group, including Paris, Tokyo, New York, Sydney and Cape Town, are urging national leaders to work with them to build a “low carbon, climate safe world”.

Although they welcomed the landmark climate deal agreed in Paris last year, they believe it is “only the first step” towards a low carbon future.

The letter states: “To limit the global temperature increase to 1.5 degrees Celsius above pre-industrial levels, global greenhouse gas emissions need to peak by 2020.

“Achieving such a rapid shift is probably one of the greatest political, economic and practical challenges faced by every national leader but you do have great allies in this task: we, the mayors of the megacities of the world.”

The mayors add cities are a “key part” of the climate solution and they have seen first-hand how their climate action brings significant co-benefits to communities – from improved public health and faster economic growth.

The letter adds: “For the major cities of the world it is already clear that the faster we move to a low carbon economy, the greater will be the improvement in urban citizens’ standards of living and the stronger and more sustained will be the economic development that makes that possible.

“That is why we are all making a commitment, as part of the C40 Cities Climate Leadership Group (C40), to set out concrete plans for how we will deliver the goals of the Paris Agreement in our cities. We want our citizens, markets and other political leaders to know that we are serious about making the Paris Agreement a reality. We call on the heads of states from our respective nation states to do the same.”