Days after US President Donald Trump said he was withdrawing from the landmark 2015 Paris climate pact, Pope Francis on Monday said that the entire world must safeguard the environment.

"We must never forget that the natural environment is a collective good, the patrimony of all humanity and the responsibility of everyone," Francis tweeted on the occasion of the World Environment Day.

Trump drew widespread condemnation when he announced on Thursday the US's pullout from the Paris accord, claiming the multi-nation pact to curb greenhouse gas emissions would harm his country's economy. 

The Paris agreement committed countries to global warming "well below" 2 degrees Celsius above pre-industrial levels and "endeavour to limit" them even more, to 1.5 degrees.

During Trump's visit to the Vatican in May, Francis gave him a copy of his 2015 papal letter or encyclical on protecting the environment, 'Laudauto Si', which Trump said he would read.

The encyclical is a searing indictment of nations' failure to take care of the earth – to the detriment of its poorest – and a call to action.

The US withdrawal from the Paris agreement could add 0.3 degrees to global temperatures by the end of the century, according to The World Meteorological Organisation and US think tank Climate Interactive.