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Apr 11 • 6 tweets • 7 min read
➡️Only 6 out of 97 scenarios in the #IPCC #AR6 WG3 category C1 ('no to limited overshoot') never cross 1.5C
➡️91 out of 97 cross 1.5C temporarily, and then go back to 1.5°C by 2100

If you read the Summary for Policymakers of IPCC AR6 WG1 (Aug. 2021), this cannot come as surprise
Below the numbers from #IPCC #AR6 WG1. Not sure if this knowledge was conciously included in "keeping 1.5C alive and within reach" messaging around #COP26.
'Overshoot' pathways (= exceedance & return) didn't make it onto the high-level #UNFCCC agenda yet
ipcc.ch/report/ar6/wg1…
The overshoot logic might also a little bit hard to detect in this #IPCC #AR6 WG1 SPM figure. That's because overshoot is quite small (0.1°C) for SSP1-1.9, while at the same time all standard RCP levels (1.9-8.5) are shown in one figure
ipcc.ch/report/ar6/wg1…
Tacitly assuming overshoot creates political flexibility. In a 2017 Nature Geoscience piece ("Define limits for temperature overshoot targets"), @andreasloeschel & I explore some of the downsides
Most recommendations have been taken up in #IPCC AR6 reports oxfordmartin.ox.ac.uk/publications/d…
#IPCC #SR15 established end point 2100 and magnitude categories (limited & high OS - peak below 2C)
Scenarios table in #AR6 WG3 contains column for cumulative net negative emissions
Still largely missing (in WG1/2): Impacts for limited & high OS pathways
Finally, once governments accept they soon have to deal with a depleted remaining carbon budget for 1.5C & decide to stick to this target, overshoot and net-negative emissions will become a 'normal' object of global climate policy
Our paper in @OneEarth_CP sciencedirect.com/science/articl…

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More from @Oliver_Geden

Oliver Geden Profile picture
Apr 4
The #IPCC #AR6 WG3 report includes a comprehensive assessment of Carbon Dioxide Removal (CDR), its role in mitigation strategies and long-term pathways, but also a techno-economic assessment of ~10 CDR methods
An ongoing 🧵
[1/n] Image
For Carbon Dioxide Removal, it's still early days in #climate policy, although there are already established methods (mainly forestry-related and soil carbon sequestration, not necessarily done to remove CO2)
In #AR6 reports, there aren't chapters dealing solely with CDR
[2/n]
There was quite some CDR coverage already in the #AR6 Special Reports on 1.5°C (#SR15) and on land (#SRCCL). In WG I, CDR was mainly assessed in chapter 5 ('Biogeochemical Cycles'), and a bit in chapter 4

[3/n]
Read 33 tweets
Oliver Geden Profile picture
Apr 4
#IPCC #AR6 Working Group III SPM and Full Report on "Mitigation of Climate Change" is now available
ipcc.ch/report/ar6/wg3/
🧵on key figures and tables from Summary for Policymakers
#ClimateReport Image
Key figures & tables from the #IPCC #AR6 WG III Summary for Policymakers
SPM.1: Global net anthropogenic GHG emissions (GtCO2-eq yr-1) 1990–2019
ipcc.ch/report/ar6/wg3/
#ClimateReport Image
Key figures & tables from the #IPCC #AR6 WG III Summary for Policymakers
SPM.2a: Regional GHG emissions, and the regional proportion of total cumulative production-based CO2 emissions from 1850–2019
ipcc.ch/report/ar6/wg3/
#ClimateReport Image
Read 9 tweets
Oliver Geden Profile picture
Mar 21
Today, we'll enter the long but final stretch for #IPCC #AR6 WG III report on mitigation - the virtual approval session, finalizing the 'Summary for Policymakers' (SPM) with governments Full Report and SPM to be published on April 4
Some insights...
ipcc.ch/meeting-doc/ip… [1/n]
First WG IIl lead author meeting took place 3 years ago, the process in itself way earlier. There've been delays because of #COVID19, but "Final Draft Report" has been submitted already in Nov 2021. The last months of work have been mainly about SPM
ipcc.ch/about/preparin…
[2/n]
There are strict confidentiality rules in the #IPCC when it comes to content, but as an intergovernmental organization, the #IPCC is quite transparent when it comes to process.
apps.ipcc.ch/eventmanager/d…
[3/n]
Read 9 tweets
Oliver Geden Profile picture
Oct 29, 2021
How will climate negotiators deal with diminishing carbon budget for 1.5C?
Some thoughts from our recent @OneEarth_CP paper "#UNFCCC must confront the political economy of net-negative emissions"
Now available #OpenAccess for 2 months
cell.com/one-earth/full… #COP26
(1/n)
Paper led by @aniruddh_mohan, co-authored with @MathiasFridahl, @hollyjeanbuck & @Peters_Glen
cell.com/one-earth/full… #COP26
(2/n)
Basic problem is quite easy to understand. We're very close to 1.5C, and even if you think it's still possible to stay within the remaining carbon budget (<500 Gt), this would mean that every country needs to reach net zero pretty soon.
#COP26
(3/n)
Read 10 tweets
Oliver Geden Profile picture
Oct 29, 2021
Remarkable framing shift ahead of #COP26

While "close to 1.5C" is politically more plausible than "limit to 1.5C", it's quite ambiguous, similarly to already established "well below 2C"

Is this the new language incorporating (initial) overshoot of 1.5C?

politico.eu/article/why-th…
Some background on #IPCC WG1 projections for threshold 1.5C crossing times under different scenarios, explained by @hausfath for @CarbonBrief
carbonbrief.org/analysis-what-…
"Constructive ambiguity" is a useful tool to reach agreement under #UNFCCC. But problematic that #ParisAgreement doesn't exclude or at least sets clear constraints for 1.5C overshoot. Creates way too much flexibility
See our 2017 @NatureGeosci piece
rdcu.be/cAqml #COP26
Read 4 tweets
Oliver Geden Profile picture
Aug 9, 2021
IPCC #AR6 WGI report on the physical science basis of climate change is out today.
Find the the Summary for Policymakers and the Full Report here ipcc.ch/report/ar6/wg1/
[1/n]
Here's a short thread on Carbon Dioxide Removal, and how the #IPCC #AR6 WGI assessment (led by @KirstenZickfeld) relates to the WGIII report (due in March 2022)
ipcc.ch/report/ar6/wg1/
[2/n]
First, some important context on remaining carbon budgets, pathways and net-zero emissions - since it doesn't make any sense to talk about Carbon Dioxide Removal (CDR) in isolation.
ipcc.ch/report/ar6/wg1/
#IPCC #AR6
[3/n]
Read 15 tweets

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