Australian billionaire Andrew "Twiggy" Forrest has slammed Donald Trump's "bulldust" on climate change, insinuating the US president is too sheltered to understand the reality of it.

"Across America, people are not venting what they tell me in private, and it's just so sad," Forrest told Today .

"You've got to be able to speak truth to power. Otherwise power is never going to hear it."

Trump declared climate change was a "con job" in an address to the United Nations earlier this week.

Forrest, a long-time champion of green energy, cited his own lived experience in Australia and the Pacific islands, including witnessing "coral reef decimation", as having granted him a closer perspective on the issue than Trump.

"Mate, you come and walk a mile in my shoes before you come out w

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