SAN FRANCISCO - Sen. Dianne Feinstein unveiled a package of legislation aimed at combating global warming, calling it the "greatest environmental challenge facing this planet."

The California Democrat's plan would require automakers to boost fuel economy, increase use of renewable energy sources such as wind and solar and force companies to lower emissions of the "greenhouse gases" blamed for warming the planet.

If action isn't taken, Feinstein said, global temperatures could rise by as much as 9 degrees, leading to massive extinction of species, rising ocean levels and an increasing number of devastating storms, floods and wildfires.

"Working together, I believe we can reduce our emissions sufficiently to stabilize the Earth's climate, minimize warming, and slow global temperature increase to 1-2 degrees to avoid catastrophic climate change," Feinstein said Thursday during a speech at the Commonwealth Club.

Feinstein has already introduced some of the legislation mentioned in her speech, including a measure requiring cars and trucks to get 10 more miles per gallon within the next decade.

A new provision would bring farmers and landowners into a "cap and trade" market system to reduce greenhouse gas emissions. Farmers and landowners who plant trees or grow biofuels such as ethanol would be able to earn emission credits that could be sold to firms that exceed emission limits.

While scientists and environmentalists back most of her proposals, the Bush administration and Congressional Republicans have expressed little enthusiasm for measures they believe are unnecessary and could hurt the economy.