There’s a narrative that seems to be developing that suggests that the requirement to reach (net) zero emissions is largely based on the high-emission RCP8.5 scenario. Since this is (according to some) no longer plausible, we should give up on our (net) zero plans, because they’re no longer necessary and will do more harm than good.
One obvious problem with this isn’t that there isn’t some boundary beyond which catastrophe ensues, and below which everything is fine. We expect the impacts to become increasingly severe as warming continues. Just because we’re unlikely to follow an RCP8.5-like pathway doesn’t mean that there won’t be severe impacts. If anything, there are already regions, and communities, that are being impacted by climate change and the difficulty of reliably estimating the impacts means that we may well be under-estimating the impacts of even the lower levels of warming.
Another issue is that there is a complex relationship between emissions, concentrations, and warming. This means that even if we don’t follow an RCP8.5 pathway, we still can’t rule out that we’ll experience levels of warming typically associated with RCP8.5 (> 4C, for example). Hence, ruling out an RCP8.5 pathway doesn’t immediately rule out RCP8.5-like impacts.
Finally, there is an element of irony to this narrative. One of the reasons why RCP8.5 has become much less likely is because of the progress that has already been made and the expectation that the promised climate policies will be implemented, and strengthened. Essentially, there’s an expectation that emissions will soon peak and start to decline. So, in some sense, the reason why RCP8.5 is much less likely than it once was is largely because we now think that we’re on a pathway towards (net) zero.
So, to suggest that the implausibility of RCP8.5 means we can give up on current climate policies is essentially arguing for a pathway that makes RCP8.5 more likely. To be clear, it’s always been a worst-case scenario, rather than being a pathway we were likely to follow. However, that’s mostly because it was unlikely that we would simply not develop, and implement, alternatives that would reduce emissions, not because it was absolutely impossible to follow an RCP8.5-like pathway.