Earlier this month Thai environmental activists carried out a ritual suicide on an effigy of DiCaprio at the Bangkok premiere of The Beach.
The 25-year-old has thrown his weight behind an EarthAction initiative to lobby governments for cleaner fuels ahead of Earth Day on 22 April.
In a statement the heart-throb said there was a "global emergency".
"The Earth is heating up and everyone's future is at risk. Please join us in sending a strong message to our governments that now is the time for action to prevent violent changes in our climate," he added.
He continues on his web page: "I can't tell you how excited I am to host Earth Day 2000 on the Mall in Washington DC... together we're going to rock this country, and jump-start some important changes that will put us on the right path for the future."
EarthAction is urging its supporters to contact their political leaders in the run-up to Earth Day, urging them to support clean energy such as wind or solar power.
Enviromnental protest
Ironically, Dicaprio has recently come under fire from ecological activists over alleged damage to a Thai island paradise during the filming of his latest movie, The Beach.
Earlier this month Thai environmental activists carried out a ritual suicide on an effigy of DiCaprio at the Bangkok premiere of The Beach.
Activists staged a mock harakiri on the star, puncturing the dummy with fake swords.
They also displayed photographs of Maya beach in southern Thailand which they allege was ruined by the film shoot last year. The protesters also urged the public to boycott the film.
A court case brought by local administrators against 20th Century Fox, a local producer and the Thai forestry department alleging damage to the beach on Phi Phi island is due to resume on 26 March.
The charges claim that the film shoot was given the go-ahead before social impact and environmental studies were carried out. A claim for compensation of more than 100 million baht (£1.6m) has been tabled.