Trump claimed the US had to make emissions cuts while big rivals didn't, allowing them to grab a "financial advantage". China's emissions are now about 29 per cent of global total, or roughly twice that of the US. But China is the world's factory, and many emissions are export-related. And on a per-capita basis, Americans each emitted 16.1 tonnes of CO₂-equivalent in 2016, compared with 7.7 tonnes for every Chinese and just 1.9 tonnes for every Indian. While the Turnbull government might declare Australia's Paris targets are among the most ambitious per person, we start from about 18.6 tonnes each in 2016, which is one of the highest.

Trump said staying in the accord would cost America $US3 trillion ($4 trillion) in lost GDP, an estimate apparently sourced from a business group , according to FactCheck.org . The US would also be exposed to "massive legal liabilities" if it stayed in. The Paris accord, though, deliberately excluded a liability mechanism so Trump's advisers may be revealing fears about America's historical contribution of accumulated greenhouse gas emissions. Michael Burger, a Columbia University law professor, reckons lawsuits have "a greater likelihood of success" challenging governments' climate inaction, FactCheck said. Costs of action, of course, must be weighed against the damage global warming is already unleashing.

Loading

International reaction has largely been to blast Trump's unilateral move and call for nations to hold their nerve and climate commitments. But the absence of US leadership makes its less likely nations will pledge deeper cuts at the Paris review due in 2018. As it is, current promises would probably deliver 3 degrees of warming this century rather than the 1.5-2 degrees limit – versus pre-industrial levels – agreed at Paris. Scientists recently modelled the difference for Australia of that half degree, and found the chances of a repeat of the 2016 mass coral bleaching in the Great Barrier Reef soar to 64 per cent in any year at 1.5 degrees of warming and an 87 per cent at 2 degrees alone.

What's next?

The Trump administration may be opting for the Paris exit ramp but major US states such as California and New York and many cities say they will stay the course. Financial markets, too, are making their own calls, which is why investors such as BlackRock have declared "coal is dead". New coal-fired power plants in Australia are viewed as "unbankable" given the need sooner or later to price carbon emissions. Still, Trump's other efforts to reverse US climate action – such as his plans to cut low-emissions technology research – make curbing warming and swapping fossil fuels for renewable energy that bit more expensive for the rest of us.