Zero Net Carbons
They do encourage people to take some responsibility for their impact on the environment, and may do a bit of good. However, I believe they create a market for entrepreneurs to enrich themselves over people's desire to do good, they often have no impact on warming (or actually increase it), and they encourage an attitude of smugness in which people no longer feel obligated to make the real changes necessary to really address the global climate change problem.
Therefore, I am coming out against the concept of carbon offsets.
The basic idea is very similar to that of purchasing "indulgences" in the middle ages. You figure out exactly how much you've sinned (e.g., polluted), and you give somebody some money calculated to exactly make up for that amount of sin. Then, you go on doing whatever it was you were doing.
The first issue is the marketing of carbon offsets by for-profit companies. Now, I have no problem with a company that makes a profit by helping people do good. However, when you provide no actual service or goods to your customers except a slip of paper, I'm not convinced I would ever give you my money. This is the route that Al gone has taken, although I'm pretty sure that in his case the concept is much more complex than just paying someone else to conserve on his behalf.
Suppose you purchase your offsets from a reputable non-profit? There's still very little you can do to verify the actual carbon savings being generated on your behalf. You may be able to find out what sorts of things your money's being invested in, but the details of the net carbon impact may be elusive.
Take for example, planting trees, one very popular method of reducing carbon. In fact reforestation in the tropics turns out to be a pretty good and cheap strategy, as long as the right kinds of trees are planted (likely quick-growing, hopefully native species), local farmers aren't kicked off their land, and a host of other human rights problems don't emerge.
But planting trees elsewhere could actually increase climate change. Reduced reflection of sunlight can increase warming more than the cooling effect of the carbon absorbed. The act of planting trees can release carbon stored in the soil. The carbon stored in the trees will be released as soon as the trees are harvested or burned. And maybe those trees were going to be planted anyway, and someone is just using the carbon offsets to make money off the transaction.
What about buying pollution credits? Well, how can you verify that the company wouldn't be reducing their pollution anyway, for cost, regulatory or other reasons?
I assume that there are some good things that can be done with carbon offsets. Things like investing in renewable energy, or methane storage. But you have to be able to convince yourself that these things wouldn't be happening anyway without your purchase of offsets.
But the fundamental problem with carbon offsets is that they allow people to buy their way out of caring about their impacts on the planet. I may drive 20,000 miles every year, but by spending $150 I can assuage my conscience and go about my daily life with no change. In essence, I'm paying someone else to drive less for me.
So if people shouldn't buy carbon offsets, what should they do?
Well, first of all look hard at your own impacts. Drive less. Turn off your AC. Make your house more efficient. Start replacing light bulbs with more efficient compact fluorescent ones. As you replace appliances, choose the most efficient ones. Buy less stuff. (Every time you buy something, you are paying someone else to pollute on your behalf.) Don't go out and replace all your stuff at once, because the act of buying and shipping something new along with disposing of the old thing just adds to the problem. Recycle and compost. Go live in a cave. To really stop all of your emissions, shoot yourself. (Actually, stabbing yourself would be a more environmentally friendly way to go.)
So, you're riding your bike down to the local farmers market to pick up some locally-grown organic produce, but you're concerned that you're not down to zero. Now what?
Well, pick a cause you believe in, like renewable energy. Find a non-profit you believe in that invests in your cause. And write them a contribution. This is not an offset for your carbon emissions, it is an investment in society that you believe will make a fundamental change. Write the contribution off your taxes. Then take the money you just saved and write another check. (Actually, making your contribution electronically is probably a more environmentally friendly way to do it.) If you can, volunteer, start a company, or whatever makes sense for you.
That's it. You're working on improving your impact on the planet. You're making a positive impact in an area that matters. And, best of all, you are doing it because the cause is important to you, not because you are feeling self-centered and want to be able to claim carbon neutrality.