Is Donald Trump’s determination to send US climate change policy back into the dark ages an “existential threat to the entire planet”, as the architect of many of Barack Obama’s green measures warns? Or is global momentum towards a cleaner, safer future “unstoppable”, as the UN’s climate chief said recently?

The answer lies somewhere in between and you can choose your point on that scale according to your optimism about whether society, governments and businesses will together rise to the challenge of beating global warming.

One thing is clear, however: the slash-and-burn of federal climate action in the US is making one of humanity’s greatest ever challenges more difficult, just at the time when it needs to start getting easier.

There are lots of possible pathways to the zero-emission global economy needed in the second half of this century to avoid the “severe, widespread and irreversible impacts” warned of by the world’s scientists. But the best is to start early, with global carbon emissions starting to fall by 2020.

Encouragingly, emissions from fossil fuels seem to have levelled off in the past three years. However, Trump’s executive order undoing Obama’s clean power plan (CPP), alongside reversals making driving and fracking more polluting, might halt that progress. The US is the world’s second biggest emitter, pumping out 14% of global carbon dioxide, and canning the CPP could leave emissions 25% higher than otherwise.

But there are good reasons to think that scrapping the CPP may fall a long way short of delivering the huge coal revival Trump has promised. Even the coal barons themselves don’t see that happening.

Across the decades that energy investments stretch, the global move is clearly towards low-carbon and around the world coal is in freefall. A Trump blip is highly unlikely to see companies make billion-dollar bets on coal. Furthermore, with the costs of solar and wind power plummeting by 85% and 66% respectively since 2009, many US states and cities see clean energy as the future, whatever the current federal administration thinks.

As Trump’s healthcare and travel ban fiascos show, doing is a lot harder than tweeting. So while his climate assault is unlikely by itself to condemn the world to runaway global warming, it will make it tougher to tame.

However, the rest of the world’s nations are not going to give up just because the US is choosing to free-ride on their efforts to halt climate change. At the annual UN climate summit in late November, Trump’s election win strengthened their determination to act, not weakened it. “It really concentrated the minds of 180 of the world’s countries to get on,” one senior delegate told me.

Science is concentrating minds, too. Recent work shows the fast-heating Earth is now in “uncharted territory”, and just on Monday “human fingerprints” were revealed on extreme weather disasters around the world.

The US has brought a great deal to the international climate effort: billions of dollars of funding that helped persuade poorer nations to accept the landmark deal in Paris in 2015, as well as world-leading scientific observation and research. Trump may pull all that from the table, but there are plenty of other players ready to step up, not least the European Union and China.

China, the world’s biggest polluter, is now taking dramatic action to cut emissions, pushed by the foul air many of its citizens suffer and pulled by the likelihood of the low-carbon economy being the greatest growth story of the 21st century.

John Podesta, the former Obama chief of staff who warns of Trump’s “existential threat”, is nonetheless far from despondent: “This threat alone is no reason to give up hope that we can still avert the most severe impacts of climate change. If the US cedes its leadership in the global movement to curb greenhouse gas pollution, other major powers, most notably China, are primed to dominate the coming clean energy economy.”

It is also far from fanciful to imagine other nations penalising future US goods if they are produced with dirty energy. Politicians are already talking about such border carbon taxes and might point to the astronomical tariffs the US imposes on imports of which it disapproves, such as Chinese steel.

It is doubtful that Trump’s blitzkrieg on “bullshit” climate change will herald the end of civilisation. But, given the issue’s critical importance for all nations and their unprecedented cooperation to date, it might just signal the end of the US’s dominance as the world’s pre-eminent political and economic power, with others taking up the mantle. Trump’s campaign pledge was “Make America great again” – his legacy could be “Made China great again”.