Oscar-nominated British actor Pete Postlethwaite stars in "The Age of Stupid", which was shown in a solar cinema tent in Leicester Square and beamed to more than 70 cinemas nationwide via a live satellite link.
The event's organisers said they hoped up to 16,000 people would watch the premiere - but discouraged anyone from flying to London to see it.
Postlethwaite turned up in a solar car to the premiere, which was also attended by actress Gillian Anderson, designer Vivienne Westwood - on a bicycle - and Energy and Climate Change Secretary Ed Miliband.
In the film, Postlethwaite plays an old man living alone in a devastated 2055, looking back on archive footage of 2008 and asking why no one acted to stop climate change.
"The Age of Stupid", which opens here on March 20, took 3.5 years to make and had a budget of just 450,000 pounds (500,000 euros, 630,000 dollars) provided by 228 individual investors.