If Earth Matters to you, It was about a decade ago that carbon offsets became a “thing.” Travelers at San Francisco International Airport could step up to a kiosk and buy carbon offsets to balance out that greenhouse gas-spewing flight. (How does 1,000 pounds of CO2 on an LA-to-Chicago trip sound?) The idea of an offset is that you can cancel out the harmful effect of your emissions by supporting a project that will eliminate an equivalent amount of emissions elsewhere in the world. But offsets pose practical and moral problems: If harmful pollution is wrong, can you really right that wrong by paying someone else not to pollute?