The Canadian Football League announced plans in November to make the Grey Cup a "carbon neutral" event. The following month, Aeroplan unveiled a venture that would allow its members to neutralize the environmental impact of their jetliner travel. And when Hollywood attends the Oscars on Sunday, the awards show will declare its presenters have a carbon footprint of zero.

In each case, the move toward environmentalism is largely accomplished by the purchasing of "carbon offsets," which in theory allow a buyer to balance its greenhouse-gas emissions by sending money to a seller that uses the money to invest in a business that does the environment some good.

The carbon-offset market was non-existent just a few years ago, but it is big business now, with researchers estimating the activity in North America at more than $100-million last year. So, what are the buyers getting for all that offset money? At best, they are spurring investment in an enterprise that reduces greenhouse-gas emissions. At worst, critics say, they are simply practising chequebook environmentalism, salving guilt by investing in a scheme whose benefits are negligible.