Additionality means that it wouldn't have happened without the offset. It's nice that we should or need to do X, but if X isn't going to happen, then any action

Additionality means that it wouldn't have happened without the offset. It's nice that we should or need to do X, but if X isn't going to happen, then any action that causes X to happen is a positive change. If it's a "valid" offset, then we already know X wasn't going to happen without it, regardless of whether it should or must happen. Double counting is a serious problem here, of course, and the article is right that removal based offsets alone cannot get us to net zero. What genuine offsets (i.e. those that actually meet the 4 required criteria) can do is that (finite) resources get invested where they're more effective, letting us achieve specific intermediate goals earlier than without them. That's actual kilograms of CO2 that aren't in the atmosphere by a certain date. "If Everyone Did It, Would It Still Work?" - until we actually get to net zero, yes, actually. As the cheap and easy opportunities go away, genuine offsets become much more expensive, to the point where avoiding the emissions will often be cheaper than offsetting them. Likewise, as regulation tightens towards net zero, the opportunities for offsets that meet the "additionality" requirement go toward zero too. There are many serious issues with offsets (like the lack of additionality, double counting, non-permanence, and leakage, as mentioned in the article), but the article makes it sound like they can't work even theoretically. "“Preserving an acre of rainforest” fails the test. Suppose all of the world’s cement plant operators agreed to offset their emissions this way. Suppose that this succeeds so well that 100% of the world’s remaining rainforests are protected forever." - then the offsetting potential of rainforest protection is exhausted, and other ways to get to net zero will need to be found. Also, the "additionality" criterion should, if applied correctly, already limit the amount of offsets you can get out of protecting the rainforest.