Thread by @AukeHoekstra

We have another 'winner': a study claiming RCP 8.5 is 'business as usual' when in fact it is highly unlikely. In @NatureClimate no less.

RCP 8.5 is NOT business as usual!
STOP printing that misleading claim!
theguardian.com/environment/20…

If you're new to RCP 8.5: it's a scenario used by the IPCC with assumption on CO2 emissions.
en.wikipedia.org/wiki/Represent…
It means we assume 'forcings' of 8.5 W/m2 in 2100.

People started calling this 'business as usual' even though by now most scientists think it's highly unlikely.

In the abstract the paper calls RCP8.5 'high' and RCP4.5 'mitigation' which sort of muddles the misinformation. But again: nobody should call RCP8.5 'business as usual'.

We had a long twitter discussion on this using the hashtag #RCP85IsBollox instigated by the tweets of @MLiebreich and the research of @jritch with a nature commentary by @hausfath and @Peters_Glen.

TL:DR
Saying RCP8.5 is 'business as usual' is misleading.
nature.com/articles/d4158…

Does that mean polar bears are fine?
Of course not!
The north pole ice is really rapidly shrinking.

Does that mean there is zero chance this scenario comes true?
Again, no!
And as an insurance policy we should invest to lower the chances on such worst case outcomes.

And I DO understand you want to highlight things could go horribly wrong.

So why does a climate hawk like me undermine the credibility of this story??

Because it is not true!

That should be enough in my opinion.

Two other reasons:

1) By giving people worst case prediction while pretending they are 'business as usual' you expose all serious scientists working on climate mitigation to the accusation of lying and being alarmist.

Don't think for a moment fossil interests won't use that.

2) This makes it look as the trajectory we are currently on is already mitigation. It basically means politicians can give a few handouts to clean energy and then pat each other on the back for achieving the mitigation scenario in the paper (RCP 4.5).

So please @NatureClimate and others, make sure you publish no more papers containing the phrase 'business as usual' to describe RCP 8.5. (And no, not 'reference scenario' either.) Maybe 'highest scenario' or 'worst case scenario'. Can you do that for us?

Have to mention one more thing: in AR6, the RCPs (how much forcing) is combined with SSPs (en.wikipedia.org/wiki/Shared_So…). In most IAMs RCP 8.5 is considered valid only in SSP 5 (fossil fueled development) and e.g. not in SSP 2 (intermediate).

In normal English: you need a combination of worst case warming AND a specific set of social circumstances to achieve the scenario that is so casually defined as BAU in this paper @NatureClimate just published. 'Highest emissions' is a less misleading term for that than BAU.