Tiring of its mission to "organize the world's information," Google has set itself a new objective: save the planet.

The search giant unveiled a US$4.4 trillion plan Wednesday to reduce the US's dependency on fossil fuels and embrace alternative energy. The proposal would yield a net saving of US$1 trillion by 2030 and slash US carbon dioxide emissions by 48 percent, according to Google, which said it had been busy "crunching the numbers."

The plan involves weaning the US off of coal for producing its electricity and turning to wind, solar and geothermal power instead. It would also cut oil use in cars by 40 percent and use electricity for personal transportation. Google said its goal in announcing the plan, called Clean Energy 2030, was to stimulate debate.

"With a new Administration and Congress -- and multiple energy-related imperatives -- this is an opportune, perhaps unprecedented, moment to move from plan to action," the company said.

It's the latest and perhaps most ambitious attempt by Google to shape public policy. The company has already weighed in on issues like worker immigration, intellectual property law and net neutrality. Energy is further from its expertise, but Google has been hiring experts to help with the task, including the lead author of the proposal, Jeffery Greenblatt, a former scientist with the US Environmental Defense Fund.

CEO Eric Schmidt was to present the proposal in San Francisco on Wednesday evening. Google also described the plan in a blog posting and in more depth on its Wikipedia-like Knol Web site.

It deals primarily with two areas -- electricity production and personal vehicles. The basics look like this:

Reduce energy use today: Naturally for Google, it starts with computers. Data centers and personal computers both can be operated much more efficiently, by unplugging PCs when they are not in use, for example. Building codes can be more aggressive, and "smart meters" in homes that give real-time pricing should encourage people to use less power. Pacific Gas & Electric is already installing such meters in northern California.

Electricity: The US today produces half its electricity from coal, 20 percent each from natural gas and nuclear energy, and 1.5 percent from oil. The plan would replace coal and oil with primarily wind, solar and geothermal energy (using heat from inside the earth). It calls for keeping electricity demand at today's level, which would lop 30 percent off the projected demand in 2030. Onshore and offshore wind would account for a further 29 percent of demand, solar 12 percent and geothermal 15 percent. Nuclear, hydro and natural gas would make up the rest.