"Women are very immediately affected, and usually women and children can't run away," said Maathai, who won the 2004 Nobel Peace Prize for her work on sustainable development.

"Men can trek and go looking for greener pastures in other areas in other countries ... but for women, they're usually left on site to face the consequences," she said. "So when there is deforestation, when there is drought, when there is crop failure, it is the women and children who are the most adversely affected."

Maathai was in Washington with 1997 Nobel Peace laureate Jody Williams, who got the award for her work in creating an international treaty to ban landmines, and both spoke to reporters at a briefing.

Williams said she saw climate change as a threat to security, and said desertification of former agricultural land fueled the conflict in Darfur.

Climate justice
In that case, she said, women forced to move for political and environmental reasons were more at risk than men.

As the leader of a United Nations mission on Darfur, Williams said she visited a vast refugee camp in neighbouring Chad where water was scarce and women and girls were dispatched to get water from outside the camp.

"Why did the women have to go?" Williams asked. "Because if the men went, they'd be killed. If the women go, the only, only thing they have to face is rape."

"If you don't deal with development and climate, you will have an increasingly insecure world," Williams said. "But if you're going to deal with it, you need to deal with it in terms of climate justice."

That meant rich countries, including the United States, must cut their own pollution and greenhouse emissions – not just offer aid for environmentally sound development.

Maathai, who founded the Green Belt Movement that started as a tree-planting program and grew into an international human rights and environmental organisation, said the United States has taken a "back seat" on global environmental leadership.

"As long as the United States of America doesn't take its leadership position, the rest of the world hides behind her and wants to say, 'she is the greatest polluter, she isn't doing anything, why should I do something?'" Maathai said.