If you've heard celebrities, politicians, and even friends buzzing about how they've eliminated the negative environmental effects of their car or plane travel by going 'carbon neutral' or using 'offsets,' you may be wondering exactly what they're talking about. What most people mean when they speak of carbon offsetting is the notion that planting trees will remove -- or at least balance out -- carbon dioxide released into the atmosphere when we drive cars or heat our homes. Another incarnation of offsetting declares that emissions circumvented through increased energy efficiency (say, driving a hybrid or installing better insulation) are 'savings.'

If you're still scratching your head, wondering how compensating for a gas-guzzler with a sapling and some fluorescent light bulbs adds up to a cleaner environment, you may be on the right track. While these steps could indeed make Mother Earth happy, critics say that offsets aren't a pass to continue our travel-filled, wasteful lifestyles unabated. In fact, some argue, they may not even work.

In an effort to clear the confusion, WorldChanging -- the website on all things sustainable -- solicited Dr. Ron Dembo of ZeroFootprint (the company hired to offset WorldChanging's current book tour) and journalist Clive Davidson to write a response to criticisms of the offsetting system. Dembo and Davidson address the important conundrum that offsetting may actually encourage us to pollute by eliminating the guilt associated with it. The team proposes that offset companies should also require some reduction in emissions overall.

For ZeroFootprint, the answer seems to be use less and offset the rest. A New Internationalist piece by Adam Ma'anit, however, takes a more skeptical view, arguing that the logic behind offsetting is 'hotly disputed.' Trees are, at best, a temporary storage place for carbon dioxide. When they die -- naturally, by fire, or through harvesting -- the carbon is released back into the atmosphere from which it came. Carbon removed from the ground in fossil fuels, however, is released into the atmosphere permanently.

And according to Ma'anit, even if climate offsets did work, they still cause harm by enabling projects or justifying lifestyles that should be reined in. What's more, the exotic tree species often planted as offsetters rarely absorb the amount of carbon they are projected to -- perhaps because many of them die in habitats they weren't bred for -- and they have been known to degrade the land they are planted on. Added to that is the fact that the entire business is steeped in encroachment on native land in the global South, where the trees are planted, though some clever marketers now promote commandeering of the land as positive 'development.'