The biggest news in the Global Carbon Budget 2021 is a very large downward revision in CO2 emissions from land use
The downward revision is about the same size as the total emissions of CO2 from fossil fuels from the EU17 or India
Of course caveats about uncertainties . . .
Compared to when I went to sleep last night, our perception of the magnitude of the net-zero challenge just improved (it is stull huge, but less huger than we thought)
This is absolutely great news
As a consequence of the updated understandings 2021 CO2 emissions are now lower than any year 2011-2019
In other words, flat for a decade
Again, very good news
The revision also moves the world a giant step further away from RCP8.5
For those who rely on massive increase in land use emissions to argue for RCP8.5?
Schwalm et al 2020 = RIP
Good news!
Finally, while LUC is undoubtedly important, we are reminded that the net-zero CO2 challenge is fundamentally one of energy production technologies (carbon intensity of energy for you Kaya wonks)
Keep your eye on the ball
/END
PS. For those scoring at home, I just sketched this out
RIP SGD20, RIP RCP8.5
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I'm lecturing in class today on this brilliant paper by Mike Hulme
"Climate reductionism is the means by which the knowledge claims of the climate modelers are transferred, by proximity as it were, to the putative knowledge claims of the social, economic, and political analysts"
Hulme observes, correctly, that climate reductionism can be found in the scenarios of the IPCC which fix society and vary climate ... this is common in the climate impacts literature (eg, when adaptation is ignored)
We see climate reductionism in the IPCC15 report where societal impacts of 1.5C are compared to 2C (as reported yesterday by NYT below)
Little known is that almost all of these differences in impacts occur under scenarios that ignore human adaptation ... as if
The publication today of the 2021 FCCC NDCs reinforces the utter implausibility of CMIP/IPCC baseline scenarios (7.0, 8.5) unfccc.int/sites/default/…
It also should mark the last time anyone cites Schwalm et al 2020 to defend RCP8.5/SSP5-8.5 as BAU (or even as plausible)
Absolutely huge news
UN FCCC expectations for 2030 GHG emissions
2016 INDCs = 62.0 Gt CO2-eq
2021 NDCs = 51.5 Gt CO2-eq
Net-zero is a massive challenge, of course, but compared to 5 years ago the world is now in a much better position that was expected unfccc.int/sites/default/…
Another systemic misuse of the RCP scenarios involves using RCP8.5 as a reference scenario and the others as mitigation scenarios in impacts, economic or policy studies
RCP creators warned against doing this when RCPs were created
But it is found everywhere, including IPCC
Scenario experts foresaw that this type of misuse was getting baked into the RCP methodology, drawing 4 scenarios from different models and renaming them as if they were comparable (when they weren’t)
The desire for RCP pathways of radiative forcing overrode considerations of the proper use of scenarios for impacts, economics, policy research
The perceived needs of climate modeling were explicitly expressed as the priority
🧵
Why are climate scientists so mad at me?
Here's one answer
For almost 30 yrs I've been writing abt the conflicts between (a) the special interests of the climate science community and (b) the broader social responsibilities of this community
Pretty normal STS fare ... read on
My 1994 PhD dissertation was an evaluation of the then newly-created US Global Change Research Program link.springer.com/content/pdf/10…
I argued that the USGCRP would do a lot of good science but have limited policy relevance (a conclusion later reached by a @theNASEM study)
I was a post-doc at NCAR when this paper came out
It resulted in a furor
NSF funded NCAR & the program officer who oversaw NSF funding was central to creation of USGCRP
My job was threatened
A huge debate ensued
UCAR leaders pushed back on the pressure
I kept my job
A preview...
Scenario misuse in climate science is far deeper and nuanced than semantics of reference scenarios (as some would have us believe)
They are also very pedestrian mistakes, common to efforts to use scenario methods in research
Not surprising or unique to climate, but significant
The petulance, name-calling and invented quotes we saw earlier today suggests that our first recommendation won't be easily taken😉
Easier to attack messengers than hear their messages
We all all suffer the consequences when science gets off track and some try to keep it there
The responses I've had today the this discussion have me optimistic that the powerful few gatekeepers in the climate space of 2009 are not so powerful in 2021
The teeth gnashing & name calling remains the same, but most now see it for what it is, and that's good news