When I started the Green Belt Movement [an NGO that combats deforestation by training rural Kenyan women to plant trees] in 1977, I was starting a small project. But it moved from one step to another. We've since planted more than 30 million trees [earning Maathai a Nobel Prize]. It's been very surprising.
It is in the interests of the developed world to help Africa adapt to climate change. People from poor regions are not going to sit there and die of starvation; there will be large migrations of people seeking a new life in the developed world.
Africa isn't just asking for help; she has something on the table, too, in the way of carbon management: the Congo forest is a huge carbon sink. But international companies are logging there, as the government needs the money. If it had another revenue source, this would stop.
You cannot get rid of poverty, improve quality of life and eliminate diseases without taking care of the environment, so you can have adequate food and clean drinking water.
Being a woman in Kenyan politics has meant I have not been able to do as much as I wanted. Men are quick to tell the voters you can't do as much as they can.
Serving others is the greatest thing one can do with one's life. I have been able to make a difference in people's lives. Even to plant a tree that will be growing long after you are gone is very satisfying.
I'm an optimist. I'm always hopeful and working for change, and I'm sure sooner or later a new horizon will beckon.
It's important to forget everything for a moment. It's easy when busy to forget you have a body, not a machine, and it needs replenishment. Resting, going to the gym and basking in the sun are some of the moments when I can relax.
'The Challenge for Africa' by Wangari Maathai (Heinemann, £20) is out now