Billionaire Michael Bloomberg is investing another $30 million (£20.5m) in a bid to help the US reduce its dependence on coal.

The cash will go towards environmental group Sierra Club’s ‘Beyond Coal’ campaign, which aims to replace half of the nation’s coal fleet with clean energy by 2017.

It builds on Bloomberg Philanthropies’ previous commitment of $50 million (£34m) in 2011, bringing the total to $80 million (£54.8m).

The initial grant was used to expand the campaign from 15 states to 45 states, enforcing environmental laws and helping communities impacted by coal mining and coal plants.

It claims for every 50GW of coal taken offline, more than 3,600 deaths and 60,000 asthma attacks could be prevented and $2.3 billion (£1.6bn) saved in health care costs every year.

The former mayor of New York City said: “The single biggest reduction in carbon pollution in the US has come by retiring and repurposing coal-fired power plants – and that’s the direct result of our Beyond Coal campaign.

“But much more work remains and today we are doubling down on what has proven to be an incredibly successful strategy for improving public health and fighting climate change.”

Michael Brune, Sierra Club Executive Director added: “Together, we have secured the retirement of 187 dirty power plants – we cannot and we will not stop there. With this new investment, a clean energy economy is in our sights and dirty coal is a thing of the past.”