By Alex Kirby
BBC News website environment correspondent, in Nairobi
Wangari Maathai, who won the 2004 Nobel Peace Prize, says African governments should do more about climate change.
Professor Maathai says Africa's women "carry a heavy burden"
Professor Maathai, also Kenya's deputy environment minister, was speaking to African journalists at the United Nations Environment Programme HQ here.
She said climate change mattered, and the Kyoto Protocol on how to limit its effects must be taken seriously by all.
Professor Maathai, an environmental and human rights campaigner, will receive the peace prize in Norway in December.
She is the founder of the Green Belt Movement, which has planted 20-30 million trees in Africa to counter forest loss and slow the spread of the deserts.
Challenge to backsliders
Mrs Maathai told the journalists, attending a climate workshop organised by Unep's GRID-Arendal office: "There's no reason why our African governments can't control greenhouse emissions, but quite often we make excuses.
"We say, for example, we're poor and so we can't impose taxes. But should we be taxing people trying to earn a living?
"When we act, we challenge those who are not doing as much as we think they should. I'm trying to educate the Kenyan government, and sometimes I have to do it loudly."
She criticised the way in which firewood and charcoal cost people less than electricity. "In the long term", she said, "using wood will cost us more. It's a very expensive resource.
"The tree is an empowering symbol: when you've planted one, something happens to the environment. It's not the only solution, but it's something most of us can do.
Trees for remembrance
"Anyone can dig a hole. And one tree multiplied several million times gives you a forest."
Professor Maathai said many Africans did not understand the problem of climate change.
"We need to explain it to them in simple terms and to give them simple solutions," she said. "When a baby is born, or when someone dies, plant a tree."
Winning the prize had made "a lot of people open their eyes. Many wondered why a highly educated person would spend their time digging holes and planting trees.
"But this is a matter of life and death, and the Nobel committee has made a wonderful decision."
Mrs Maathai lamented the decline of traditional knowledge and the neglect of African species.
She said: "Much of our knowledge and experience is not in books but in our cultures, and that's why I'm concerned about their loss.
"We import seeds, not from this environment but for instance maize from the Americas. Every year we're dealing with a new hybrid.
Trees can galvanise people, Maathai says
"I don't know how far we'll go till we rediscover the sorghums and millets and pumpkins that are indigenous to Africa."
And she was far from convinced that African men were leading the continent well.
Professor Maathai said: "We women in Africa carry the burden of poverty and conflict. We see our children dying in the fields, we see the future slipping away.
"I've been calling on Africa's leaders, who are mostly men, to make sure resources are exploited for the people's benefit, to help them out of poverty, ignorance and disease.
"We've been waiting for men to change. We women have an important role in challenging them to be responsible to us and to our children - to stop sending them off to die on the front lines."