As the world’s factory floor, China is not an obvious environmental leader. It is beleaguered by severe pollution and generates more carbon emissions than any other nation. Yet many have trumpeted it as an emerging “green giant” for its non-carbon-based energy production and its aggressive promises to cut carbon emissions. New York Times columnist Thomas Friedman described China’s “green leap forward” as “the most important thing to happen” at the end of the first decade of the 21st century.

But the facts do not support this “green” success story.

China indeed invests more than any other nation in environmentally friendly energy production: $34 billion in 2009, or twice as much as the United States. Almost all of its investment, however, is spent producing green energy for Western nations that pay heavy subsidies for consumers to use solar panels and wind turbines.

China was responsible for half of the world’s production of solar panels in 2010, but only 1 percent was installed there. Just as China produces everything from trinkets to supertankers, it is exporting green technology — which makes it a giant of manufacturing, not of environmental friendliness.

In wind power, China both produces and consumes. In 2009, it put up about a third of the world’s new wind turbines. But much of this has been for show. A 2008 Citigroup analysis found that about one-third of China’s wind power assets were not in use. Many turbines are not connected to the transmission grid. Chinese power companies built wind turbines that they didn’t use as the cheapest way of satisfying — on paper — government requirements to boost renewable energy capacity.

Consider the bigger picture: 87 percent of the energy produced in China comes from fossil fuels, the vast majority of it from coal, the International Energy Agency found in 2010.

The explosive recent growth in Chinese solar and wind generation equates to going from zilch to a small fraction: Wind today generates just 0.05 percent of China’s energy, and solar is responsible for one-half of one-thousandth of 1 percent.

The avoided carbon emissions from all of China’s solar and wind generation — even maintained over the entire century — would lower temperatures in 2100 by 0.00002 degrees Fahrenheit. That is the equivalent, based on mainstream climate models, of delaying temperature rises at the end of the century by around five hours.

Of course, proponents argue that China has promised to do much more: It vowed to cut carbon intensity (the amount of emissions produced per dollar of gross domestic product) 40 to 45 percent by 2020. But this is essentially promising to do nothing new: IEA projections, using expected growth and development and absent any new policies, show carbon intensity already on track to fall 40 percent. Even with this reduction, by 2020 China will have quadrupled its emissions from 1990.

China also aims for non-fossil-fuel energy sources to account for 11.4 percent of primary energy consumption by 2015. At best, this is a promise to slide backward merely slowly. Today, China gets 13 percent of its energy from non-fossil fuels, particularly biomass and hydropower, with a little nuclear energy and a minuscule amount of solar and wind power.

The reason China does not use more wind and solar power is simple: Even when mass-produced with cheap labor, solar panels and wind turbines are not cost-effective replacements for fossil fuels. They appear so in the West only where politicians create generous subsidies for their implementation.

There is, however, a mostly untold story from China that shows an area where the promise of a “green future” is not without foundation. China leads the world in the production of solar heaters. This industry doesn’t receive subsidies because it doesn’t need them: Solar heating is cost-effective.

Heat constitutes almost half of global energy demand, much of it from households wanting to cook, heat water or warm their environments. Solar heaters can heat water cheaply — at about one-quarter the price of an electric water heater. In China, solar heaters provide four times more energy than wind turbines. Exports of this product bring in more than $6 billion a year.

Because solar heaters are cheaper than fossil fuel heating, consumers don’t need to be paid large subsidies to use them.

This is the green lesson China holds: A green future will result not from subsidizing immature technology today but from developing competitive green technology that is effective and cheap. Wind and solar power are not yet competitive. Research would be a much better investment for Western countries than subsidizing imports of today’s green technology from China. Until we can make alternative energy technology effective and affordable for everybody, there will be no happy ending to the “green” success story.

Bjorn Lomborg is director of the Copenhagen Consensus Center and the author of “Cool It: The Skeptical Environmentalist’s Guide to Global Warming.”