Donald Trump’s Twitter pledge to make a decision on whether to remain in the Paris climate agreement this week promises resolution to months of fevered lobbying over US involvement in the global accord.



But while America’s traditional allies and environmental groups continue to urge Trump to stay within the Paris deal – in which nearly 200 nations have pledged to limit global temperatures to a 2C (3.6F) increase on the pre-industrial era – the actions of the US president, most recently at the G7 meeting in Sicily, have begun to provoke murmurs that perhaps the world would be better without American involvement.

The final G7 communique saw the US unusually break with the other six nations by failing to commit itself to the Paris agreement, which Trump promised to “cancel” during the presidential campaign, and reports on Wednesday claimed he had decided to exit. The exasperation of European leaders suggested they are ready to move on with or without the world’s second largest emitter of greenhouse gases.

“The whole discussion about climate has been difficult, or rather very unsatisfactory,” said German chancellor Angela Merkel. “Here we have the situation that six members, or even seven if you want to add the EU, stand against one.”

The US formally turning its back on perhaps the last best chance of a coordinated response to climate change would certainly carry heft. Frantic calculations by several thinkthanks and universities have estimated that US withdrawal would add up to 3bn tonnes of extra carbon dioxide to the atmosphere every year, raising the global temperature by 0.1C (0.2F) to 0.3C (0.5F) by the end of the century.

Such a regression would be compounded if other countries took the United States’ lead and also decided to quit Paris, or at least not strive to fill the void in emissions reduction. This would have grave implications for coastal cities facing sea-level rise, parts of the world already blighted by heatwaves and food insecurity, and the planet’s endangered species.

While US emissions would start to level off rather than continue their gradual decline, there are signs that India and China, the two other national heavy hitters in emissions, are moving away from coal more quickly than expected, according to Climate Action Tracker.

This has led several economists and large US businesses to fret that the coming boom in solar, wind and other renewable energies will not take place in the US. China signaled its intent earlier this year by announcing it will invest $360bn in renewable energy by 2020, creating more than 13m jobs in the sector.

If the economic fallout of leaving the Paris deal does not sway Trump, the diplomatic and security ramifications may. Rex Tillerson, the secretary of state, has urged the US to “keep a seat at the table” in order to maintain its international standing, while UN secretary-general António Guterres has raised the possibility of “risks of conflict” if climate change is not properly addressed.



If Trump does decide to stay in the deal, it is likely he will attempt to “renegotiate” it, which would mainly involve the US revising down its goal of reducing emissions by 26-28% by 2025 based on 2005 levels. Opponents of the deal, such as Trump strategist Steve Bannon and Environmental Protection Agency chief Scott Pruitt, have framed Paris as a “bad deal” for the US that may even hinder Trump’s domestic agenda of winding back various environmental regulations.

Several independent legal experts, as well as those who helped craft the Paris agreement, reject this view, pointing out that the edifice is built on a series of voluntary non-binding goals submitted by countries. Paris is essentially a statement of intent, a signal from governments to their citizens and businesses that low-carbon economies are on the way and that this inevitability should be financially supported.

Some supporters of Paris are now wondering how useful it would be to have a disengaged US within such a structure. The American public is largely in favour of the Paris deal and could be given the misleading impression that their government is addressing the climate issue by simply staying put, despite tearing down Barack Obama’s climate policies such as the clean power plan at the same time.

“Wanting the US to remain is a short-sighted, knee-jerk reaction,” said Luke Kemp, an expert in international environmental policy at the Australian National University. “The international community should be much more worried about the real domestic actions of the US, rather than whether it is symbolically cooperating internationally.”

Kemp points out that the US could act as a drag upon the international climate effort if it doesn’t leave. “The US and the Trump administration can do more damage inside the agreement than outside it,” he said.

The momentum is reportedly with the “leave” faction, with a group of 22 Republican senators – minus the notable voices of Lindsey Graham and John McCain, who want the US to remain – urging Trump to make a “clean break” from Paris. On Tuesday, Trump again met with Pruitt, one of the most vociferous opponents of the deal.

But the White House’s confusion over the decision and its wider ramifications was perhaps summed up best by Sean Spicer, Trump’s spokesman, who on Tuesday was asked the simple question of whether Trump believed global warming was spurred by human activity, a subject he has previously vacillated upon.

“Honestly, I haven’t asked him,” Spicer replied. “I can get back to you.”