United States President Donald Trump was to decide this morning on pulling out of the Paris climate agreement, a move which would isolate the US in global efforts to curb the warming of the planet.

Here are five things to know about the pact.

Q What is the Paris climate agreement?

A It was established during a 2015 United Nations-led talks in the French capital, and legally ratified last year. In joining the climate accord, the 195 signatories pledged to reduce greenhouse gas emissions. But they were given ample leeway in how much they planned to cut them by.

Q Why is the US threatening to leave the pact?

A Mr Trump apparently believes that remaining in the accord would harm the US economy; impair the creation of jobs in areas such as Appalachia and the West, where his strongest supporters live; and undermine his "America first" message, the New York Times reported.

Q How have other nations responded?

A World leaders have expressed dismay at Mr Trump's climate stance, following the recent Group of Seven summit in Sicily.

The US had refused to sign onto a statement of support for the Paris accord approved by all other G-7 participants.

Q When will President Trump announce his decision?

A He was to announce his decision at 3pm on Thursday US time, or 3am today Singapore time.

Q What will happen if the US leaves?

A The departure of the US, the world's largest economy and second-largest greenhouse gas emitter, would not dissolve the pact.

But it could trigger a cascade of events that would have profound effects on the planet.

Other countries that were reluctant to join the pact could retract or soften their commitments to reducing planet-warming pollution, CNN reported.