Efforts to reduce carbon dioxide emissions in China may be backfiring--at least in the short term.

Next month the country faces a self-imposed deadline to reduce its carbon intensity (a measure of the amount of carbon dioxide emitted per unit of GDP) by 20 percent compared to 2005 levels. In a last minute dash to meet these targets, some local governments have started imposing planned blackouts.

While the blackouts are cutting emissions from power plants, they're having unintended consequences. Factories, which have to keep running to meet production requirements or face fines for missing deadlines, are getting their power instead from backup diesel generators. These emit carbon dioxide and running them has led to a diesel shortage. Thousands of fueling stations have reportedly shut down or refused to sell drivers more than half a tank of diesel fuel. To make up that gap, Chinese refineries are producing more diesel--a strain in a country that has to import most of its oil.

Of course, unintended consequences from efforts to reduce carbon dioxide emissions aren't limited to China. In the United States and Brazil, the use of food crops for biofuels can drive up food prices and lead to the destruction of forests as new land is cleared to make up for lost food production. Clearing that land also results in more carbon dioxide emissions, undoing much of the benefit of biofuels.

Ethanol made from sugar cane rather than corn (the main source of ethanol in the U.S.) results in far less carbon dioxide emissions. But Dan Sperling, director of the Institute for Transportation Studies at the University of California at Davis, estimates that when you figure in the impact of cleared rainforests, that benefit could disappear.

Fossil fuels are the backbone of economies worldwide, so governments spend a lot to support them. A new report from Bloomberg New Energy Finance says altogether governments spent between $43 anf $46 billion on renewable energy and biofuels last year, not including indirect support, such as subsidies to corn farmers that help ethanol production. Direct subsidies of fossil fuels came to $557 billion, the report says.

This disparity raises the question--if the report is right and fossil fuels require so much backing, can they compete with renewables without government support? After all, some renewables--such as sugarcane based biofuels and some wind farms--can already compete with fossil fuels. Without the huge government subsidies for fossil fuels, wouldn't they be eclipsed by renewables?

The answer, for now, is no. So far renewables just can't provide enough fuel and power to displace fossil fuels. The infrastructure to make and distribute them isn't adequate, and many renewables have shortcomings that can make them difficult to work with--solar panels, for example, only generate electricity when the sun is out. If the fossil fuel subsidies disappear, gasoline and electricity prices will increase. That will help renewables compete, and increase in scale, but it will take years--likely decades--for them to reach levels high enough to replace all fossil fuels.