Leonardo DiCaprio's passion for environmentalism was inspired by Al Gore.

He shared: "At a young age, I was very saddened by species that had become extinct by the result of man-made activity and so that led me on a long sort of journey to get me involved in environmental issues."

DiCaprio, 41 - who has spent years raising awareness about global warming - revealed how one conversation with Gore, who served as the US vice-President under Bill Clinton, shaped his attitude.

He told People: "It was really a meeting that I had with Al Gore in the White House in my early 20s.

"He sat me down, drew a picture of the planet, drew our atmosphere and said, 'This Is the most important crisis facing humanity' and from that point on I really become not only fascinated with the issue but really concerned why we as a collective world community haven't done enough about it."

Despite the work he has already done in the fight against global warming, DiCaprio admitted the battle is far from over.

The 'Wolf of Wall Street' star explained: "Each year is getting hotter than the next and now is the time to act on this issue. We are at a real turning point, not only in human history but as far as the manipulation of our planet is concerned due to global emissions. We need political leaders to really take a stand."