I want to offset my carbon footprint, but I'm not sure what company (if any) is really making effective changes. Bill Gates says he pays $400/ton of CO2 he offsets - but the companies I've seen imply I can make my entire footprint of around 30 tons per year disappear for $150. That doesn't really line up. And with this being a product that isn't tangible I worry about the likelihood of being taken advantage of. How would I ever know if they're using my money in bad faith?

I've held off on buying any offsets so far because of these concerns.