"We have reduced the (carbon emission) cost of somebody going into space from something like two weeks of New York's electricity supply... to less than the cost of a economy round-trip from Singapore to London," Branson told reporters in Singapore.
The founder of the diversified Virgin group was in the Southeast Asian city-state to attend a summit organised by the Carbon War Room, an environmental charity organisation he founded in 2009.
"New technology can dramatically reduce the carbon output and that is the challenge we have set ourselves," added Branson.
The SS2's lightweight carbon-fibre body will also "reduce fuel burn dramatically", he said.
The SS2, with two pilots, is designed to be launched by a transport plane called White KnightTwo and will be guided by a rocket motor before gliding back to Earth.