So the author, by switching to local fonts, reduced the carbon emissions of the Internet by 0.000000056%.
Well yeah, one person switching to low-impact techniques on a low-traffic site won't change much. But (as with any other positive intervention), if lots and lots of people (say 50 percent of website owners, by traffic volume) reduce their footprint by 40 percent of so -- then that's a different story now, isn't it?
According to the Carbon Fund you can offset your CO2 emissions for $10 per metric ton.
Red herring, different topic. It's agreed by now that, whatever benefits offsets may bring (and this is hotly debated) -- we absolutely have to reduce emissions at the source as well.
If that point isn't 100 percent clear by now - then there's not much left to talk about, now is there.