If Donald Trump is re-elected as US president in November, there will be a less than 0.1% chance of the world limiting climate change to a 2°C increase above pre-industrial levels, according to climate researchers.

A study published in the June issue of peer-reviewed scientific journal Environmental Science & Policy shows that four more years of climate inaction by a US government will cause “knock-on effects on other countries’ emissions” and could ultimately delay global emissions reduction by a decade.

“While the 2°C goal will likely be reached only under a very small set of conditions in any event, even temporary US withdrawal will further narrow this set significantly,” say the study’s authors, from the CICERO Center for International Climate Research in Norway and the Potsdam Institute for Climate Impact Research in Germany.

The researchers used an “agent-based” computer model — a kind of virtual world where countries interact — to analyse the potential impacts of continued climate inaction by the US government.

More than one million scenarios were run by the computer model, using different combinations of inputs — including how other countries respond to US inaction — and found that the 2°C global target was hit less than 0.1% of the time.

However, when the model was run without a second Trump term, the 2°C goal was only met 0.3% of the time — and if Trump had never been elected, it was only hit on 0.64% of the scenarios.

If all countries’ meet the emissions-reduction pledges they made under the 2015 Paris Agreement, the world would still be on course for a temperature increase of around 3°C, which would have a devastating impact on the planet’s ecosystems and food production, with rising sea levels displacing 275 million people living in coastal areas.

Keeping climate change to less than a 2°C rise above pre-industrial levels is seen as a far safer threshold, albeit nowhere near as safe a 1.5°C temperature increase.

The Paris Agreement committed the 195 signatories (including the US) to “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above preindustrial levels”.