There’s been some recent debate about the term ‘net-zero’. Just to give some basic background, given that the zero emission commitment is close to zero (i.e., when we get anthropogenic emissions to zero, global surface temperatures should soon stabilise) means we can define a carbon budget. This tells us how much more we can emit if we want some chance of staying below some temperature target. It also tells us that our emissions must go to zero. The complication is that this could occur through emissions actually going to zero, or through some kind of negative emission technology offseting some continued human-caused emissions (this could include some active land management).
What some are concerned about is the possibility that some future negative emission technology could allow some to make ‘net zero’ promises that they may not be able to keep, or never actually intended to keep. In other words, they will claim that they’re aiming to get to a stage where they are offsetting all of their emissions despite it not yet being known if such technologies can actually operate at a suitable scale. Essentially, this becomes a form of greenwashing.
Another problem, though, is that some are interpreting ‘net zero’ in ways that aren’t consistent with what is intended. Mark Carney, for example, claimed that a company for which he is vice-Chair was ‘net zero’ because their enormous renewables business had avoided emissions that were comparable to their actual emissions. However, this isn’t ‘net zero’, it just means that they’ve ended up emitting about half of what they might have emitted.
‘Net zero’ requires actively sequestering an amount comparable to the amount actually emitted, not avoiding emitting an amount comparable to how much was actually emitted. I managed to come up with a reasonably popular tweet that illustrated the problem with Mark Carney’s suggestion.
I also came across another complication today, where someone interpreted ‘net zero’ as being the point when actual emissions are offset by negative emission technologies and by natural sinks. If this means that there is no net emission of any kind (anthropogenic, or natural), then it would imply constant concentrations. However, the reason that the zero emission commitment is probably small is because the natural sinks continue to take up some of our emissions after our emissions have gone to zero so that atmospheric CO2 concentrations actually decrease.
If we get to a stage where atmospheric concentrations stabilise, then we would actually continue to warm (this is the constant concentration commitment, which is different to the zero emission commitment). Hence, ‘net zero’ in this context means ‘net zero’ anthropogenic, not ‘net zero’ anthropogenic and natural. I should make clear that the above interpretation was, I think, more some confusion about ‘net zero’ than any attempt to define it in some convenient way, but it does illustrate how this can be a tricky concept.
So, I can see why some are concerned about the term ‘net zero’ and, as Simon Lewis points out, we can’t solve climate change using accounting tricks. However, I do think that the term ‘net zero’ is fine and that we should be careful of changing terminology just because some aren’t using it appropriately. However, it is important to stress that ‘net zero’ means ‘net zero’ anthropogenic emissions and that in the absence of negative emission technologies ‘net zero’ is the same as real zero. In other words, if negative emission technologies are unlikely to operate effectively at scale, then ‘net zero’ requires simply getting anthropogenic emissions to zero.
Warming commitments – post of mine about warming commitments with a number of useful links at the end.
Mark Carney Walks Back Brookfield Net-Zero Claim After Criticism – article describing Mark Carney’s misinterpretation of ‘net zero’.
The climate crisis can’t be solved by carbon accounting tricks – Guardian article by Simon Lewis.