Feeling guilty about that greenhouse-gas-spewing flight to visit Aunt Gladys in Minneapolis? That SUV sitting in the driveway? How 'bout all that nice warmth coming out of your electric baseboard heaters?

Well, carbon offsets are for you! The premise is simple: Plunk down some cash for the companies who sell these, and they'll balance out all that carbon dioxide your actions have let loose in the atmosphere. You can see Aunt Gladys guilt-free.

These companies, though, do a variety of things with the money you pay, and critics say many don't actually offset the guilt-spewing gases at all. For example, American firms involved in this field often use the proceeds to invest into renewable energy enterprises, such as wind farms or geothermal energy ventures.

That definitely does some good. Assuming those enterprises actually get up and running, they displace some of the future demand for energy whose emissions will warm the world.

But, critics say, they do not reduce the absolute amount of greenhouse gases being produced right now. In fact, critics say, because they are purchased by people who are eager to reduce their impact, offsets may result in even more of the gases being released than otherwise would have been -- because those committed people go on about their normal, carbon dioxide-splurging ways as before instead of cutting back.

Originally many of the carbon offsets were geared toward tree-planting, which does help suck carbon dioxide out of the atmosphere. But increasingly, because of the unwieldy and uncertain administration of those -- How long do the trees have to stay in the ground? Who will be around in 50 years watching to make sure? -- companies that sell the offsets have shifted toward funding renewable energy.

The basic problem with the offsets for now is that for many of them, there's no formalized and regulated market for them. It's all voluntary.

There is one more-regulated market, one authorized by the Kyoto Protocol, the international treaty to reverse growth of greenhouse gas emissions. It authorizes what's known as a "clean development mechanism," which is supposed to ensure that projects for which credit is given are actually in addition to whatever else would have happened anyway.

However, a June 2007 investigation by The Guardian newspaper of London found that the United Nations-sponsored program "has been contaminated by gross incompetence, rule-breaking and possible fraud by companies in the developing world, according to UN paperwork, an unpublished expert report and alarming feedback from projects on the ground."

How can you choose the right carbon-offset program? Check out this guide from Tufts University and the Stockholm Environment Institute.

Reprinted with Permission of Hearst Communications, Inc. Originally Published: Carbon Offsets