In an open letter yesterday, hundreds of top scientists including famous physicist Stephen Hawking, warned against voting for Republican presidential nominee Donald Trump, saying it would be disastrous for the planet if he becomes the US president.

Trump, who once claimed global warming is a hoax "created by and for the Chinese", vowed in May that he would pull out of the historic Paris Climate Agreement if he wins the US presidential election in November, reports The Huffington Post.

Opting out of the pact would have "severe and long lasting" consequences, both for the planet and the US, wrote the 375 members if the US National Academy of Sciences, including 30 Nobel laureates, in the letter.

"Human-caused climate change is not a belief, a hoax, or a conspiracy. It is a physical reality," the scientists wrote in the letter.

"During the Presidential primary campaign, claims were made that the Earth is not warming, or that warming is due to purely natural causes outside of human control. Such claims are inconsistent with reality," the letter read.

"A Parexit would send a clear signal to the rest of the world: 'The United States does not care about the global problem of human-caused climate change. You are on your own," the letter also stated.

Although the letter did not mention Trump by name, it is a clear attempt to steer the Americans away from casting their votes in his favour, reports The Huffington Post.

Earlier this month, the Paris Agreement was officially ratified by the US and China, the two largest emitters of greenhouse gases in the world, which was a major step for the deal to take effect this year. 

More than 170 nations signed the Paris Agreement in April, with the aim to fight climate change by reducing carbon emissions.

Former Harvard biology professor EO Wilson, often referred to as the 'father of biodiversity', is one of the signees who said earlier this month that his "main worry right now is that the Republican candidate might win the election", reports The Huffington Post.

"The United States can and must be a major player in developing innovative solutions to the problem of reducing emissions of greenhouse gases," the letter also read.

"Nations that find innovative ways of decarbonising energy systems and sequestering CO2 will be the economic leaders of the 21st century. Walking away from Paris makes it less likely that the US will have a global leadership role, politically, economically, or morally. We cannot afford to cross that tipping point," it added.