NAIROBI, Kenya (Reuters) -- The United Nations and Africa's Nobel laureate, environmentalist Wangari Maathai, launched a project on Wednesday to plant a billion trees worldwide to help fight climate change and poverty.

Kenya's Wangari Maathai, who in 2004 became the first African woman and first "green" activist to win the Nobel Peace Prize, urged people from the United States to Uganda to plant trees to combat global warming and to make a long-term commitment.

"Anybody can dig a hole, anybody can put a tree in that hole and water it. And everybody can make sure that the tree they plant survives," she said on the sidelines of a U.N. meeting on climate change in the Kenyan capital, Nairobi.

"There are 6 billion of us and counting. So even if only one-sixth of us each plant a tree, we will definitely reach the target (next year)," she told reporters.

Maathai, 66, became Africa's best known environmentalist after her Green Belt Movement planted about 30 million trees around Africa in a drive to slow deforestation and erosion.

Her work was praised by the Nobel committee as a step to help end poverty and avert potential conflicts over scarce building materials and firewood.

Some 189 nations are meeting in Nairobi to explore options for a global agreement to combat climate change, which experts say is worsened by rampant deforestation around the globe.

Achim Steiner, the head of the U.N. Environment Program (UNEP), said the delegates' discussions were important, but also complicated, slow and hard for the average person to follow.

"But at the same time as governments negotiate, citizens can act," he said. "Planting trees is a win, win, win, win, win proposition, and there are few of those in our world today."

Steiner said planting a billion trees would soak up some 250 million tons of carbon dioxide warming the atmosphere.

"It is a gesture more powerful than any report we can produce, or any political statement we can make," he said. The United Nations offered encouragement but no funds for the initiative.

For advice on what types of trees to plant in which environment, scientist Tony Simons said people could check interactive maps with details in scores of languages on his group's Web site http://www.worldagroforestry.org.

Some 32 million acres of forest are cut down every year, mostly in Africa and South America, and Simons said that could have dire consequences for everyone in the world.

"If you put your head inside a black plastic rubbish bag and breathe in and out five times, that is what the CO2 concentration is going to be like in 50 years if we don't start planting more trees," Simons said.