Want an offset? Want to change the world?

There are many who believe, with justification, that carbon offsets are snake-oil, green-washing, fake. Surely, you cannot take out enough carbon dioxide from the atmosphere with $100 to compensate for a year's worth of living?

Well, for most things, like planting trees in temperate forests, buying credits from the Chicago Climate exchange, and subsidizing the cost of wind and solar power plants--I now don't buy it either.

Here's my logic. Forests in temperate zones absorb sunlight, heating the earth and aiding global warming in the short-term. Now, we should not cut down forests here to slow global warming--releasing the carbon in forest soils is a huge no-no. BUT adding additional forests up north does not help much.

We need to add, or protect, tropical forests. Over 25% of global carbon emissions comes from burning tropical forests--more than all the cars in the world. In many poor countries, old-growth forests (and often forests, period) outside parks are gone. See this great flash introduction from Conservation International.

Buying $100 worth of carbon credits from the Chicago Climate exchange may prevent a coal company from emitting $100 worth of carbon dioxide, or 3 tons. This is a decent offset. BUT buying credits is not going to slow down carbon emissions very much, since the purchase of 3 carbon credits will not change the price of carbon for a polluting company.

Subsidizing a wind/solar power plant makes it possible to supply electricity at competitive rates to people who are willing to pay slightly higher prices for carbon-free electricity. Although I am sure the math works out, this seems to me a very roundabout and inefficient way to prevent carbon from being released into the atmosphere.

So how could you offset your carbon, if the above methods (and companies like Terrapass and Carbonfund.org who use them) don't work?

Three words: Protecting tropical forests. Pick an area where tropical forests outside parks are being burned, etc. Find a reputable organization that protects tropical forests. Buy an acre of rainforest. One acre of rainforest contains approximately 200-400 THOUSAND pounds of carbon.

I emit around 40-100 thousand pounds annually, as I drive, fly, and buy 100s of objects shipped to me from China. This year, I bought two acres of Costa Rican rainforest from The Nature Conservancy. That's an acre for my girlfriend and I for the last two years of living. At this point, we are not carbon-neutral; in all likelihood, we are carbon-negative. The cost? $50 an acre. Land is cheap in Costa Rica, as anyone who has dreamed of escaping there knows.

Tropical forests are being lost at a mind-numbing rate; 2030 will be a much sadder place than 2008. If rich citizens and governments all start getting real carbon offsets by protecting these forests, it could change history.

Search Google ("rainforest acre carbon", or "adopt acre rainforest") and use your judgement. I personally recommend The Nature Conservancy's Adopt-an-Acre program; they have an 88% efficiency with your money. But they all do great work--the Rainforest Alliance and Conservation International come to mind.. For those interested in wildlife, there's the World Wildlife Fund, and for those who want to reforest the U.S., there's the Conservation Fund. For you Brits, there's the World Land Trust.

The fate of our planet hangs in the balance. Do the right thing.