Nobel winner Maathai sounds alarm over planet

She said sweeping changes were needed to restore a "world of beauty and wonder" by overcoming challenges ranging from AIDS to climate instability.

Maathai founded a campaign that has planted 30 million trees across Africa in a bid to slow deforestation.

"Activities that devastate the environment and societies continue unabated," Maathai, Kenya's deputy environment minister, said in a Nobel acceptance speech at a glittering ceremony in Oslo City Hall.

"I call on leaders, especially in Africa, to expand democratic space and build fair and just societies," she said.