Forgiveness is not easily bought. And it comes with unpredictable costs. This was the lesson the Roman Catholic Church learned from selling indulgences, a practice during the 13th to 16th centuries in which sinners could purchase absolution for their temporal transgressions and thereby be excused in the eternal hereafter. Aside from the dubious theological economics — the Church argued it had an excess of good deeds to sell — the practice eventually culminated in religious wars that fractured the Church and produced Protestantism.

The contemporary equivalent of selling indulgences is buying carbon offsets to undo the environmental sin of emitting the CO2 that is causing global climate change.

As personal guilt ascends in tandem with the ominous warnings about rising CO2 levels, many people are attempting to assuage their growing moral discomfort by buying back theirtransgression with deeds that compensate for their carbon output. Indeed, a whole industry is forming to accommodate this practice. The earliest and most obvious is with the world’s airlines, probably because most flying done by the public is unnecessary. And secondly, according to the David Suzuki Foundation, because airplanes have “a disproportionately large impact on the climate system” (Globe & Mail, May 30/07), accounting for “4 to 9 percent of the total climate-change impact of human activity”.

Some passengers, such as those flying with Air Canada or WestJet, can now compensate for their flight’s CO2 production by purchasing offsets with their tickets. If a return trip from Toronto to Paris generates 1.2 tonnes of carbon dioxide per person, then a guilty conscience can be eased by contributing $20.35 to a tree-planting project in Maple Ridge, BC — this is Air Canada’s present version of offsets.

But offset calculations are difficult to make because they depend on the size and efficiency of the aircraft, the passenger load, and even the altitude flown. A person flying for 10 hours in an Airbus 310 — it holds about 75,000 litres of fuel, burns 7,000 litres per hour and carries about 220 passengers — would be responsible for about 890 kilograms of carbon dioxide. A similar flight in a new super-jumbo A380 that carries 310,000 litres of fuel and 525 passengers would produce 1,520 kilograms per person. Flying the same trip in a Boeing 747-400 would generate 1,935 kilograms per person. Some climatologists contend that high altitude emissions should be multiplied by 2.7 because the carbon dioxide emitted at this elevation cannot dissolve in the oceans, be absorbed by trees and soils or be captured by other biological processes; it stays in the atmosphere for 50 to 200 years and goes directly to heating the planet.

As with honesty in religious matters, the issues surrounding carbon offsets are more complex than simply receiving absolution by paying money. The planting of trees to offset airplane flights or driving — or the burning of any fossil fuels — tries to replace the immediate environmental damage of carbon dioxide release with tree-growth that might take 50 to 80 years to sequester the equivalent amount of carbon. In the interim, the trees could be cut down, consumed by forest fires or disease, or they could even be displacing other plants that might store carbon more efficiently. Guy Dauncey, president of the Victoria-based BC Sustainability Association, says that, “Tree-planting for offsetting is something I absolutely disapprove of [because] scientists are telling us we need a turnaround of global carbon emissions in 10 to 15 years” (Globe & Mail, May 30/07). However, Dauncey does support offsets that fund the preservation of old growth forests because this sequestered carbon will not be released by cutting down and processing the trees.

Dauncey, who is becoming an internationally recognized authority on climate change and sustainable economies, has other useful advice. “The rule with offsets is that the action taken would not otherwise be done,” he says (Ibid.). If a wind farm or solar facility is already being planned and financed, your offset contribution will do no additional good. To be certain that your offset will produce a real reduction in CO2 emissions, be sure that the reduction would not otherwise have happened. This criterion is called “additionality”.

Daucey’s general advice is, “Offset your past emissions. Reduce your future emissions” (Econews, Apr/07). His own preferred offset program is to contribute $10 per tonne of his CO2 production to the Solar Electric Light Fund (www.self.org). A project such as this provides solar electricity to poor and remote villages in Bhutan and Nigeria. It has the multiple benefits of reducing the burning of unhealthy kerosene, alleviating poverty and providing villagers with light for nighttime reading and study. Clearly, choosing your offset is a complicated but personal matter.

As with all sinning, determining the cost is also complicated and personal. Once you’ve decided where to invest your offset, then you must decide how much to pay. The airlines have estimated your carbon cost at about $10 per tonne, a price that most people are willing to pay without being dissuaded from flying.

But many ecologists consider $10 per tonne for offsets to be little more than a symbolic gesture that relieves conscience but has few other benefits, a token payment that does not discourage carbon dioxide production. If we must reduce global CO2 output by 80 percent by 2050 to avoid environmental havoc, then the price of carbon sinning will have to be considerably higher. Some suggest $200 per tonne, an amount that would represent the actual cost to human health and natural ecologies, as well as the wars, widespread pollution and diverse environmental damage caused by our addiction to fossil fuels.

If bad deeds are to be undone by good ones, we have some very serious reckoning to do. And the cost of salvation will not be cheap.