Humans should have fewer babies to help mitigate climate change, argue scientists including well-known conservationist Jane Goodall.

"It's our population growth that underlies just about every single one of the problems that we've inflicted on the planet. If there were just a few of us, then the nasty things we do wouldn't really matter and Mother Nature would take care of it -- but there are so many of us," the 75-year-old English scientist told Agence France-Press in an interview.

"We should be talking about somehow curtailing human population growth," said Goodall, a United Nations Messenger of Peace, whose 1960s research on chimpanzees altered views on the relationships between humans and animals. "It's very frustrating as people don't want to address this topic."

The controversial topic was not addressed at the United Nations' climate summit in Copenhagen in December. Powerful groups such as the Catholic Church oppose contraception, and others see population control efforts such as China's one-child policy as totalitarian. Even some climate scientists see limited value in it, because most greenhouse gas emissions come from developed countries with small growth rates.

Still, like Goodall, other scientists, advocacy groups and lawmakers argue that slowing population growth could be key to fighting climate change.

The United Nations Population Fund's 2009 annual report links slower population growth to reduced greenhouse-gas emissions.

"The whole world has been talking about carbon credits, carbon trading and emissions targets. But not enough has been said about the people whose activities contribute to those emissions," the report says. "Unless climate policies take people into account, they will fail to mitigate climate change or to shield vulnerable populations from the potentially disastrous impacts."

In December, more than 60 members of Congress, citing in part the need to address climate concerns, urged the Obama administration to improve financing for family planning efforts in a letter to Peter Orszag, director of the Office of Management and Budget.

A report in September from the London School of Economics found that contraception is almost five times cheaper than conventional green technologies such as windmills or solar panels at combating climate change. It cites U.N. estimates that 40% of pregnancies worldwide are unintended.

"Stabilizing population levels has always been essential ecologically, and this study shows it's economically sensible, too," said Roger Martin, chair of the Optimum Population Trust, which commissioned the report.

The non-profit Trust, of which Jane Goodall is a patron, campaigns for family planning, sex education and women's rights. It advocates that couples voluntarily "stop at two."