You’ve probably heard about "green tags," whereby businesses — or events, or rock bands, or whatever — can offset the carbon emissions of their activities by paying for clean energy credits (debits?). As the preceding sentence (doesn’t) make clear, it’s not entirely easy to explain exactly what a green tag is, or what it does, or how to get one.

Now a whole host of websites have popped up offering to let you offset your own personal CO2 emissions — that is, your driving. But the services of said websites work with different figures, cost different amounts, and produce different results. What’s a confused, eco-conscious driver to do?

Fear not. Joel Makower has just written a fascinating and comprehensive summary of the whole "climate-neutral driving" schtick. Get thee and read it.