All you need to know: What is the Paris Accord? Why is Trump walking away? And why should you care?
Donald Trump has vowed to pull the US out of the Paris Accord citing its "draconian" financial and economic burdens.
The move has been roundly criticised by politicians and scientists across across the globe.
What is the Paris Agreement?
It is a global deal, agreed under the United Nations in the French capital in December 2015, which will see action by all countries to curb rising temperatures.
Under the accord wealthier countries, like the US, agreed to help developing nations by providing climate finance to assist in adaptation and moving to renewable energy.
There will be five-year reviews of each country's emission targets, which can only be scaled-up in ambition and not reduced.
The ultimate aim is to limit greenhouse gases emissions to the level that they can be naturally absorbed by trees, soils and oceans, so-called 'carbon neutrality', between 2050 and 2100.
Why do we need it?
If the world continues to pump greenhouse gases into the atmosphere on current trajectories we are facing global temperatures of more than 4C above pre-industrial levels by 2100.
The World Health Organisation predicts that 250,000 people will die every year due to the health effects brought about by a polluted and warming planet, as malaria and dengue fever spread to new regions and food production is affected.
The World Bank adds that five of the 10 most vulnerable cities at risk from rising sea levels are in the US, with tens of millions threatened in Miami, New York, New Orleans, Tampa and Boston.
Why did Donald Trump pull the plug?
Mr Trump told the media last night: "We're getting out," at a ceremony in the White House Rose Garden in which he decried the Paris Accord's "draconian" financial and economic burdens.
He said American withdrawal "represents a reassertion of American sovereignty".
Mr Trump tapped into the "America First" message he used when he was elected president last year, saying: "I was elected to represent the citizens of Pittsburgh, not Paris.
"We don't want other leaders and other countries laughing at us any more. And they won't be," Mr Trump added.
"In order to fulfil my solemn duty to protect America and its citizens, the United States will withdraw from the Paris climate accord," he said.
How did the world respond to Trump's decision?
With Mr Trump's action, the United States will walk away from nearly every nation in the world on one of the pressing global issues of the 21st century.
The pullout will align the United States with Syria and Nicaragua as the world's only non-participants in the accord.
The condemnation was quick and unflinching.
The leaders of France, Germany and Italy issued a joint statement last night to say that the Paris climate accord cannot be renegotiated as Mr Trump has demanded.
Declaring their "regret" at Mr Trump's move, President Emmanuel Macron, Chancellor Angela Merkel and Prime Minister Paolo Gentiloni said they remain committed to the "irreversible" accord and regard it as "a cornerstone in the co-operation between our countries, for effectively and timely tackling climate change".
To all scientists, engineers, entrepreneurs, responsible citizens who were disappointed by the decision of the US: pic.twitter.com/qxjPX8MhKt— Emmanuel Macron (@EmmanuelMacron) June 1, 2017
Former US president Barack Obama was instrumental in brokering the deal and, in a statement, he expressed regret over Mr Trump's action.
"The nations that remain in the Paris agreement will be the nations that reap the benefits in jobs and industries created. I believe the United States of America should be at the front of the pack," Mr Obama said.
"But even in the absence of American leadership; even as this administration joins a small handful of nations that reject the future; I'm confident that our states, cities, and businesses will step up and do even more to lead the way, and help protect for future generations the one planet we've got," Mr Obama added.
The Irish Government "is extremely disappointed and concerned that the United States has decided to withdraw from the Paris agreement", Climate Action Minister Denis Naughten said last night.
Mr Naughten warned: "We are all vulnerable to the impacts of climate change and we all have a responsibility to address climate change within our respective capabilities.
"This is a major setback for the international community and it is essential that the decision of the United States does not weaken global resolve," he said.
What happens to the agreement now that the US is out?
The Paris Agreement sought to limit average temperature rises to no more than 2C above pre-industrial levels, and to pursue efforts to keep them to 1.5C. Current pledges from the 195 signatories are not enough, with rises of 3.3C expected. Without the US, the world's second-biggest emitter which had vowed to reduce emissions by 26pc-28pc, it increases to 3.6C.
Is all hope lost?
Paul Melia, writing in today's Irish Independent, insists that it isn't. He says climate policies are not driven at a federal level in the US, and just because the government is halting efforts that doesn't mean that individual states will follow suit.
Renewable energy targets and plans to reduce emissions are in states which are home to more than 200 million Americans. Oil-rich Texas has solar power.
California leads the way with its climate policies. Massachusetts has seen a 6pc growth in the clean tech sector over the last year, with well over 100,000 jobs created since 2008 thanks to progressive policies. Cities, too, are taking action.
In addition, business is adapting to the new reality. Shareholders in the world's largest publicly traded oil company, Exxon Mobil, this week backed a motion requiring the company to assess the risks from climate change to the business. Energy companies including BP and Royal Dutch Shell have spent billions researching clean energy, while Walmart claims to save $1bn a year by utilising renewable power.
China and the EU are now expected to take the lead on climate action.
In a communique expected today, a green alliance will be revealed with both sides reaffirming their commitment to taking action and accelerating the shift away from fossil fuels. The EU has long seen itself as a leader in this area, and the Paris Climate Accord would not have been struck without Chinese diplomatic efforts.