Amid frustration at President Trump’s decision to leave the Paris climate change accord, an increasing number of US city mayors have committed to running their cities exclusively on clean energy in the near future.

A recent vote by the city of Santa Barbara, California, takes the number of cities pledging to run 100% on renewable energy to 30. In a 5-1 vote councillors approved plans to switch the city’s power supply to 100% renewable sources by 2030.

Other recent signatories include Madison, Wisconsin and Abita Springs in Louisiana.

Environmental group the Sierra Club recently published a list of cities on track to become 100% powered by renewables in the next 20 years. It is running a campaign dubbed ‘Mayors ready for 100 clean energy’, encouraging mayors of all political affiliations to sign up to its clean energy drive.

Proving the idea is not pie-in-the-sky, cities including Burlington, Vermont; Aspen, Colorado; Columbia, Maryland; and Greensburg, Kansas, have already achieved 100% clean energy.

A chart showing renewable energy sources for the state of Colorado

In addition, similar targets are already in view across a number of states. A bill introduced in California earlier this year would see it accelerate current green energy plans in order to gather all of its electricity from renewable resources by 2045. It currently aims to produce 50% of its energy needs from renewables by 2030.

Meanwhile, legislators in Massachusetts are aiming for all the state’s energy demands to be met by renewables by 2050.

Clean energy has witnessed massive price drops in recent years, with solar power now the cheapest form of new electricity in many countries. More global clean energy capacity is being added annually than for coal and natural gas combined.