When President Obama announced plans this month to install solar panels on the White House, it wasn’t because any law required it; it was to set an example. When the U.S. military began using solar panels in Afghanistan, it wasn’t to avoid paying a carbon tax; it was because it costs $400 to $500 a barrel to transport diesel to bases there, and because hundreds of soldiers have died guarding supply lines. And when DuPont cut its energy use to 19 percent below what it was in 1990, says Linda Fisher, the company’s chief sustainability officer, by turning waste into fuel, making burners more efficient, and other steps, it wasn’t to stay on the right side of a cap-and-trade law. “We’ve saved $3 billion to $4 billion since 2000, so this is real money,” she says.

A year ago, CEOs, greens, and policy wonks were all insisting that to make any progress on greenhouse emissions, the world needed to “put a price on carbon.” De-jargoned, that means requiring manufacturers, utilities, oil refiners, and others who emit carbon dioxide by burning fossil fuels to buy permits to do so or pay a tax on their emissions. Without such a “price on carbon,” went the argument, renewables like wind and solar would never be economically competitive, and only do-gooders and showoffs would adopt them. So last year, when the Copenhagen climate talks imploded, and the U.S. Senate failed to pass a climate bill, progress should have come to a screeching halt.

It didn’t. For a long list of reasons, ranging from saving money to saving soldiers’ lives, business and government are cracking down on carbon. “It’s become obvious that [adopting low-carbon energy] is a business decision,” says Peter Boyd of the Carbon War Room, a “think tank/do tank” that works with industries to reduce their carbon footprint, “You don’t need politicians for this.” The motivations driving CO2 reductions:

Saving and making money. Energy efficiency is the easiest way to shrink a carbon footprint. Retrofits such as energy-efficient windows at the Empire State Building, which had an $11 million annual energy bill, will cut energy use 38 percent, save $4.4 million a year, and slash greenhouse emissions 105,000 metric tons over 15 years. The Sears Tower is tapping Chicago’s winds for energy and improving efficiency to cut CO2 emissions 80 percent and save millions of dollars. DuPont will make $2 billion this year (headed for $4 billion in 2012) selling products that go into photovoltaics, fuel cells, lightweight composites for transportation, and energy-efficient materials, including polymers that replace steel in vehicles, decreasing their weight and thus improving fuel efficiency, and Kevlar in tires to cut friction and improve mpg. “None of that has changed with the floundering of climate legislation in the U.S.,” says Fisher. Overall, HSBC projects that revenue from low-carbon technologies will reach $2.2 trillion globally, compared with $740 billion in 2009, says the bank’s Nick Robins.

Reputation risk. Next March, the EPA will require large emitters of CO2 to report their emissions. “No company wants to wind up on a list of top-10 worst polluters,” says Matt Arnold, in the sustainability practice at PricewaterhouseCoopers. “Even without a price on carbon, reducing your footprint helps with some investors and with recruiting.” No wonder 70 percent of the S&P 500 have greenhouse-gas-reduction targets.

The Walmart effect. The giant retailer sets sustainability requirements for suppliers and manufacturers. “We find that Walmart is the most powerful environmental regulator in the market,” says Arnold.

Peak oil. Although investors fled solar and wind after oil plunged from its $145-a-barrel high of 2008, “there is still an expectation on the part of investors that things will get worse” as we reach peak oil, says Jigar Shah, CEO of the Carbon War Room. Awareness of future supply problems creates an implicit price on carbon and thus an incentive to invest in renewables. In addition, he argues, “solar is inevitable not because of carbon but because it is the most effective way to reach the unelectrified poor.” Much as huge swaths of Africa leapfrogged over landline phone systems to adopt mobiles, so the rural poor will go from dung and diesel to solar and wind without stopping at coal and oil.

Which is not to say the world can sit back and hope these factors avert a climate disaster. As long as fossil fuels are subsidized, renewables will not expand as quickly as needed to reduce greenhouse emissions enough to avert ruinous climate change (Pakistani-size floods, anyone?)—namely, cuts of 90 percent from today’s levels by 2050, says Daniel Kammen of the World Bank. “Without a price on carbon, we’re fighting with only one hand,” he says. But at least we’re fighting.