Poor Prince Charles. Awarded a global prize for all he's done over the years to help protect the environment, he was criticized by the eco-lobby for his decision to fly from England to New York to pick up the honour and bask in his success. He shouldn't be flying in an exhaust-producing jet, they insisted, but staying home and taking the applause by videoconference instead. The criticism stung even the man who would be king enough that he cancelled his annual ski trip to Switzerland to make amends.

Closer to home, David Suzuki is getting grief from the eco-lobbyists for his decision to travel in a pollution-spewing bus across the country on a campaign to raise awareness of environmental decline.

These people want to make us all feel guilty for wanting to travel anywhere in pollution-producing cars or planes. If only there were a Star Trek-like transporter that would whisk us where we want to go without leaving a nasty trail of pollution behind us.

Enter the eco-logicians with a gimmick that offers travellers a way to wipe away the pangs of guilt for their pollution sins.

Two U.S. conservation groups have allied with online travel companies to offer travellers the option of buying indulgences. By making a donation, they say, we can be forgiven for the carbon dioxide left in the atmosphere by the jets we take and the cars we drive. The source of our redemption? Buying carbon dioxide sponges — also known as trees to us lay people.

Softening your carbon footprint

Here's how it works. Suppose you're planning a trip from Winnipeg to Orlando — that's about 5,472 kilometres round trip. You plug your itinerary into a carbon footprint calculator on terrapass.com, offered on Expedia.com. And voila: your portion of the fuel used by a jet travelling that distance is 68 U.S. gallons (244 litres) and your portion of the carbon dioxide created is 1,327 pounds or 602 kilograms.

If you're driving a car the same distance, you'd be responsible for 1,145 kg of carbon dioxide, or if there were two in the car, 572.5 kg per passenger, which works out to about the same pollution as flying.

The calculations are done in U.S. measures (I've converted them to metric here) because these American programs are not yet available to Canadians. Travelocity.com, which has linked up with the non-profit Conservation Fund's Go Zero program (conservationfund.org), plans to roll out a Canadian version on travelocity.ca soon, says Travelocity's chief marketing officer Jeffrey Glueck.

Go Zero asks for a donation of $10 US to offset the average trip including air travel, a one-night hotel stay, and rental car for one person; $25 to negate air travel and a four-night vacation with rental car for two people. It sends the money to the non-profit Conservation Fund (conservationfund.org), which then plants trees it says will absorb enough carbon dioxide to forgive your sins of emission.

The TerraPass is similar, with degrees of forgiveness. A "puddle jumper" costs $9.95 for a flight from Winnipeg to Orlando, or an "intercontinental" at $36.95 for a round trip from Vancouver to England.

Glueck says the average cost of planting a tree is $5, and so far Travelocity's collections have planted 4,000 trees — all of them in an area near New Orleans that was denuded by Hurricane Katrina in 2005.

But how many trees do you have to plant to suck up the smog you generate? Here's where it gets tricky. It depends on the kind of tree and where it is growing.

According to figures from the Colorado Tree Coalition (coloradotrees.org), an average mature tree reduces the same amount of atmospheric CO2 as released by a typical car driven 500 miles (or 805 km). That would mean you'd need to plant at least seven trees to atone for your Florida vacation The big question is how many years will it take a tree planted today to atone for the gunk you put in the air today? The trees being planted in Travelocity's program are "waist high" greenhouse specimens that will take a decade or so to reach maturity, but their carbon-gulping benefits could last a century, Glueck says.

There are a lot of caveats to the theory, as the British carbon tradeoff association Treeflights has found. Among the unknowns: whether the carbon is in permanent storage or only held until your tree dies.

More tree-planting programs springing up

Despite all the uncertainties, you're sure to be hearing a lot more about zero-carbon donation schemes, because there's increasing evidence that greenhouse gasses are helping to worsen global warming.

Dell Computer, for instance, recently launched a Plant a Tree for Me program that is sending donations from computer buyers to the Conservation Fund. The cost is $6 for a desktop computer, figuring the trees planted for that amount will cover the pollution caused by making the computer within 70 years. Carbonfund.org, based in Maryland, is trying to persuade all commuters to ante up an annual $99 donation to assuage their SUV guilt. And a resort in Zanzibar is promising to be a zero-carbon resort by using reclaimed stone, electric cars, and a pool filter made of reeds and run by a motor powered by the treadmills guests use in the gym. Of course, this fails to explain how you cover the air flight halfway around the world to get there.

In the short term, Travelocity's goal is to get at least 10 per cent of travellers to ante up, Glueck says. That's the proportion of travellers who already make the donations in Britain, where the concept originated a couple of years ago.

Easing your conscience

So yes, planting a tree can be a fine start to offsetting the emissions toll you produce. If it makes you feel better about flying, then by all means write the cheque.

But remember when you do that if all the planes carrying travellers across Canada were replaced by individuals in cars, it would require deforesting a lot of land to create a couple of extra lanes on the trans-Canada highway to handle all the extra traffic. And that wouldn't eliminate any of the carbon dioxide produced in the process.

Short of just staying home permanently, there are lots of things you should be looking at to be more fuel efficient and to offset your pollution day to day — and you can urge others to do the same.

One idea: about 4,000 trees were victims of this winter's wind storms in Vancouver's Stanley Park, just about the number of trees Travelocity has planted in New Orleans. The park authority will plant a replacement tree dedicated in your honour and tend it to maturity for $2,000 — but they will also take donations as small as $50.

And why let someone else do the planting? Plant some trees yourself in your hometown. Make it greener and reap the benefits directly during the rest of the year when you aren't travelling.

Wallace Immen has been travelling regularly for 25 years but he walks to work and has encouraged tree planting initiatives in Toronto.