In a HARDtalk programme broadcast on 30 October, Zeinab Badawi talks to ecologist and environmental activist John Francis.
How far would you go for your green principles?
After witnessing a massive oil spill in San Francisco Bay in 1971 when two tankers collided, John Francis was so shocked that for twenty years he gave up all motorised transport and stopped talking.
Later he walked across the United States and much of Latin America to try to inspire others about environmental issues.
But, as Zeinab Badawi asks him, was it all worth it?
HARDtalk is broadcast on BBC World News channel at 03:30, 09:30, 14:30, 18:30 & 21:30 GMT
HARDtalk is also broadcast on the BBC News channel at 04:30 & 23:30 GMT