It's a trend that counts Leonardo DiCaprio, London cabs and Al Gore among its followers: making life "carbon neutral" by tree planting and other environmentally friendly efforts to curb emissions of heat-trapping carbon dioxide.
The theme is a hot one as scientists in Paris this week prepare to issue a major report on global warming — but critics say the movement is counterproductive, even a scam.
The practicalities of "offsetting" carbon dioxide emitted when flying, driving cars, even getting married are increasingly simple.
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A growing array of companies offer to calculate how much carbon dioxide such activities give off and how much money should be given to projects that, in theory at least, will reduce emissions by an equivalent amount somewhere else in the world. It can be done in minutes online, paid for by credit card.
Opponents say offsetting gives people the mistaken impression that they can keep on polluting or that such individual efforts can solve global warming, when much more fundamental change is needed.
They also warn that offsetting companies lack oversight and transparency, and that the environment would be better served by people reducing their own pollution and demanding that governments end the use of carbon-producing fossil fuels.
The carbon neutral trend "tries to make money from tapping into consumers' guilt," said Jutta Kill of SinksWatch, an environmental group that monitors such projects.
"It's worse than doing nothing. ... Those who are in a role-model function like Al Gore do not do the movement for effective action on climate change a favor by promoting carbon offsets in the way he does."
But green business can be good business, especially when a trend is so hot: The New Oxford American Dictionary declared "carbon neutral" its "word of the year for 2006," for inclusion in its 2007 edition.
The British firm Radio Taxis Group, which runs a fleet of 3,000 iconic black London cabs and other vehicles, declared itself the world's first "carbon neutral" taxi company in 2005.
It said it would offset emissions by investing in renewable energy projects in Sri Lanka and Bulgaria and forests in Britain and Germany for a cost of about $195,000 per year.
Since then, the company says it has won new contracts worth $3.9 million from clients attracted by its green credentials.
"The cabs still have an impact on the environment," said Michelle Nunan, head of marketing. But "it's the best that you can do at the moment as far as taxis are concerned."
Climat Mundi's online "CO2 calculator" works out that a round-trip Paris to London flight for one person in economy class produces 0.2 tons of carbon dioxide.
It says the best thing is to take the train but if flying is unavoidable, the fledgling French company suggests contributing $5.31 to two projects it funds.
One provides Eritrea with stoves that burn less wood. The other helps maintain a plant near Sydney, Australia, that captures methane — another greenhouse gas — from rotting trash at an adjacent landfill and burns it to power electricity-producing turbines.
Eric Parent, an engineer who quit a steady job in waste management to start up Climat Mundi last June, says polluting without offsetting could become as frowned-upon socially as littering in public.
"It remains socially very acceptable to vacation on the other side of the world or to travel for a weekend to another country in Europe on a low-cost airline," Parent said in a telephone interview. "Growing awareness of global warming and the fact that we, as individuals, can now compensate for our emissions — which wasn't the case four to five years ago ... will, in my opinion, make traveling without compensating far less acceptable."
For newlyweds, or their guests, it offers a $230 "Just Married" pack to compensate for the 9 tons of carbon dioxide that it calculates are given off by a wedding bash for 150 people and honeymoon trip — accounting for travel, heating or other eco-unfriendly activity.
The French government is funding Climat Mundi's Eritrean stove project to compensate for this week's meeting in Paris on climate change. Bringing together some 500 people from all over the world for the conference is expected to produce some 1,100 tons of CO2.
To compensate will require some 360 stoves, said Parent. They burn half as much wood and pollute less than traditional Eritrean stoves.
Organizers of the 2006 World Cup in Germany said they would invest environmentally to offset the estimated 100,000 tons of carbon emissions caused mostly by car usage during the June 9-July 9 soccer extravaganza.
Fans were also encouraged to take public transport and only recyclable drink cups were used in stadiums.
DiCaprio in the past has offset his carbon through organizations that plant trees and is "looking at various options" for 2007, according to Chuck Castleberry of the Leonardo DiCaprio Foundation, which the "Titanic" star started in 1998 to promote environmental awareness.
The actor switched recently to a Honda Accord hybrid car and has solar panels on his Los Angeles home.