The Eiffel Tower lit up during the UN climate conference in Paris in 2015. Credit:AP/Michel Euler "Given Trump's stance on climate, a clear 'out' would have been much preferable for the climate," he said. "It is up to world leaders to be steadfast and protect the historic Paris achievement for the generations to come." 'Laughing at us' Trump said the current Paris deal would have cost America $US3 trillion ($4 trillion) with only two-tenths of a degree in warming saved, without stating the source of such estimates. Leaving the accord marked "a reassertion of America's sovereignty". "We don't want other countries laughing at us," he said, adding, "I was elected by the people of Pittsburgh not Paris."

The Mayor of Pittsburgh, though, took a different view to Trump: President Donald Trump announcing the US was withdrawing from the Paris deal. Credit:AP Ahead of the president's announcement on Thursday afternoon, US time, scientists and political leaders weighed the prospect of whether the Paris accord to keep warming to "well below 2 degrees" could survive the departure of the world's second largest emitter and the nation responsible for about a quarter of the historical pollution that is cooking the planet. "We'd have a massive legal liability if we stayed in", Trump said.

China has overtaken the US as the world's biggest carbon emitter - but so far it's vowed to stick to the Paris climate plan. Credit:Getty Images 'Act of war' Trump ignored last-minute lobbying by world leaders and many of the biggest US companies including Apple, and oil giants Exxon and ConocoPhillips to remain in the accord. Only Nicaragua and Syria are not signatories to the agreement, which draws in voluntary pledges to cut emission from 195 nations, a tally to be reduced by one with Trump's move. US billionaire and Democrats supporter, Tom Steyer, was among the fiercer critics ahead of the announcement, taking to Twitter to declare the Trump withdrawal as a "traitorous act of war against the American people": US President Barack Obama in December 2015 as the Paris climate conference got under way. Credit:Getty Images

Benjamin Sanderson, a climate scientist at the US National Center for Atmospheric Research, has estimated an eight-year delay in US climate action if followed by other nations would lead to an additional 350 billion tonnes of carbon dioxide emissions in a worst-case outcome. That would deliver at least another 0.25 degrees of warming but also make it "extremely challenging" to keep within the two-degree climate "guiderail" set by Paris. In an article for The Washington Post, Dr Sanderson said the US exit from Paris means the 2-degree goal "will effectively be nullified". Temperature rises are already about half way there, compared with pre-industrial times. "This is a good time to remember that even two degrees of change will have significant global ramifications," he said. "Temperature records of the past will be yearly events, most years will likely have an ice-free Arctic, and extreme precipitation events are projected to markedly increase." 'Not fatal'

Whether other major countries follow suit is hard to say. For now, Australia plans to stick with its international commitments, Prime Minister Malcolm Turnbull told Parliament on Thursday. Australia's chief scientist, Alan Finkel, said the exit of the US from the global accord on reducing greenhouse gas emissions would be "a blow, but not fatal". New polling data out this morning from the Lowy Institute reveal 54 per cent of Australian adults agreed "global warming is a serious and pressing problem [and] we should begin taking steps now even if this involves significant costs". That's up 18 points since hitting a nadir in 2012. While still the second-biggest emitter, the US is arguably not the most important player in how the emerging climate crisis of more extreme weather plays out. China, with almost twice the emissions of the US, is vowing to stick with Paris. Its motivations are partly diplomatic - helping to fill a global leadership void being created by an American president apparently eager to rattle long-standing ties such as with Europe. But chronic pollution in Chinese cities is another driver, and so are the huge market opportunities available to the companies that dominate the emerging markets in renewable energy and storage.

India, the other emerging economic giant, is also going to be key. Can it secure enough wind and solar energy at affordable prices - and those are halving every five years or so - to meet its growing energy needs without having to build a huge new fleet of coal-fired power stations? (Australia has an interest here too, given the coal industry's hopes to open a giant coal province in Queensland's Galilee Basin starting with the proposed Adani coal mine.) Toss in the towel? So is it time to throw in the towel, and accept Trump's Paris exit as game over for climate action, and consign our futures - let alone our children's and later generation's - to runaway global warming? John Cook, an Australian now working as an assistant professor at the Center for Climate Change Communication at George Mason University in Virginia, past research shows people tend to take their cues from leaders. "We saw this in Australia. In 2007, Prime Minister Rudd characterised climate change as the great moral challenge of our time," he said. "But when he failed to back up his lofty words with action, public concern about climate change fell."

"On the other hand,..it's my hope that Trump's actions (or lack thereof) will strengthen the resolve of other countries to work together to reduce emissions, rather than be used as an excuse to fail to act," Professor Cook said. Loading It's worth recalling that the Paris conference in late November almost didn't happen. Terrorist attacks in Paris two weeks before the event killed 130 people and injured about 370 others. And yet, the leaders didn't flinch, turning up in the French capital in even greater numbers than expected. Something like that rallying spirit is needed now, and in the weeks and years ahead. But that can't be left to leaders of course - it's going to hinge on the actions of voters and consumers everywhere.