That trip to Paris, those weekend drives to the beach and the balmy-in-the-winter, cucumber-cool-in-the-summer climate inside your house come at a price, and not just on your credit card or gas bill.

These activities emit greenhouse gases, including carbon dioxide and methane, which contribute to global warming. At, you can calculate your carbon footprint and buy offsets to compensate for it. Plug in information about your car, air travel and home energy usage, and the calculator will spit out the amount of carbon dioxide your habits use per year, and the amount you could pay to mitigate those emissions.

For example, I drive about 12,000 miles annually in a 2003 Honda Civic with a manual transmission. Total: 7,826 pounds of carbon dioxide. Ouch, that’s nearly four tons.

I didn’t fly much last year, just one roundtrip, direct flight from RDU to Philadelphia. Total: 382 pounds of CO2. I don’t feel so bad.

My 975-square-foot home uses electric and gas, and based on a monthly average of $60 for each, it uses 14,479 pounds of CO2. That’s less than two Hondas’ worth.

Total: 23,000 pounds of carbon dioxide, which costs $136.85 to offset.

A carbon offset represents reducing one metric ton (2,205 pounds, a bit more than the U.S. ton) of carbon dioxide emissions. When you buy one$5.95 per 1,000 pounds of reductionsthe money goes toward Terrapass projects in farm power, landfill gas capture and wind energy. For example, this year, offsets are helping reduce levels of methane at the Robeson County Landfill near St. Pauls, N.C.

Please don’t use offsets as a way to assuage your footprint guilt (presuming you have any). Offsets should supplement your conservation, such as keeping the thermostat lower when you’re not at home and walking or biking instead of driving.

Update: A reader noted that Home Depot now accepts and recycles used compact fluorescent light bulbs (see “Eureka! A low-mercury light bulb“); so if your county hazardous waste drop-off site is inconvenient, there is an alternative.