America's coal industry has been in decline for decades

It takes longer to pull out of the Paris accord than it does to withdraw from the EU, so President Trump's decision is going to stick around until the next presidential election.

By then, we'll know what sort of an impact it will have had upon the American economy.

For one thing, we'll have seen whether he managed to reinvigorate all those coal mines.

Donald Trump said the accord was "punishing" America's coal industry, with a resultant loss of jobs.

:: Anger as US quits climate deal 'to save jobs'


But few believe that withdrawing from the Paris accord will actually reverse that decline.

For one thing, the coal industry has been declining for decades for the simple reason that power stations don't need the product.

Natural gas is cheaper and cleaner. Solar power is growing. America leads the way in shale gas, and is also developing wind and hydro power.

The US simply doesn't need as much coal any more - these days, only around 27% of the energy used by America's power grid comes from coal-fired power stations, and that figure has been declining for a long, long time.

What is the Paris agreement?

Coal-fired power stations have been closed, and there are no plans to build any more.

Yes, Mr Trump is correct that a new coal mine will open shortly, but it will employ a maximum of 100 people, and produce specialist coal for steel production.

:: World leaders condemn Trump's climate change u-turn

In fact, there is only one way that Mr Trump could really have helped the coal industry in his country, and that was by hobbling the rest of the energy sector.

Instead, he's signing forms to allow more drilling for natural gas, which will end up pushing down the price of gas and make coal-mining even less viable as a business.

The fact is that, even if the US had stayed in the Paris accord, it would probably still have met its climate change obligations, thanks to emission controls and a greater reliance on renewable energy.

And twice as many American voters work in the solar energy industry than in coal.

Mr Trump is resolute, though, that he will no longer abide by the strictures of the Paris accord, and maintains that pulling out will help the US economy, saving jobs, stimulating production and ensuring a reliable source of energy.

He says the decision will save the US trillions of dollars, although it's hard to find any reliable data to back that up.

His analysis appears to be guided by a widely criticised report from an organisation called NERA, which included a series of extreme assumptions such as every other country in the world missing its climate change targets and almost no development in electric cars.

Trump on climate agreement: 'We're getting out'

Neither of those things is likely to happen.

So what will happen next?

Many American businesses have already indicated that they intend to pursue the same programme of emission reductions that they were previously following - companies from General Motors to PepsiCo, and from Shell to Microsoft - all have expressed disappointment about Mr Trump's decision.

What's more, several US states have already talked about some form of independent enforcement of the Paris accord.

In the case of California, that's particular significant - its economy is thought to be the sixth biggest in the world, sandwiched between the UK and France.

As long as California maintains existing emissions rules on, for instance, cars, there is little chance of any auto manufacturers reversing the trend towards cleaner engines.

What's more, California is talking about sharing carbon credits with China - a potentially incendiary deal bringing together America's biggest Democratic stronghold with the nation's greatest economic rival, which also happens to be the world's biggest polluter.