The @UN#HLEGReport on Net-zero Emissions Committments is out
The problem though: #IPCC 1.5C pathways don't reach net zero GHG emissions by "2050 or sooner", but by the end of the century. The famous "net zero by 2050" (better "early 2050s) is CO2 only un.org/en/climatechan… 1/
You might be in disbelief, but have a look at the #IPCC AR6 WG3 Summary for Policymakers, Table SPM.2:
For 1.5C with no or limited overshoot (category C1), pathways reach net-zero CO2 in 2050-2055, but net-zero GHG in 2095-2100 ipcc.ch/report/ar6/wg3… 2/n
The difference between net-zero CO2 and net-zero GHG can be explained by the dominant role of non-CO2 GHGs (methane, nitrous oxide, f-gases) in residual emissions and the dominant role of CO2 in removals
You can see the difference betw net zero GHG (left) & net zero CO2 (right) also in #IPCC AR6 WG3 fig SPM.5: for 1.5C with no/limited overshoot, net-zero GHG emissions by 2095-2100, net-zero CO2 by 2050-2055. Almost completely ignored by #climate policy community so far #COP27 5/n
A major reason for these surprisingly late net-zero GHG years: the high number of scenarios in IPCC database from ENGAGE project, where IAM teams deliberately explored pathways that stay at net-zero CO2 (and therefore don't reach net-zero GHG) rdcu.be/cZiZj#COP27 6/n
In ENGAGE modelling intercomparison project, IAMs looked at avoiding 'peak & decline' scenarios involving the need for high levels of net negative CO2 emissions (to return from overshoot). Therefore, they are highly ambitious in the short-term rdcu.be/cZi15#COP27 7/n
Large share of ENGAGE scenarios in #IPCC WG3 database (not a statistically controlled sample) has a counterintuitive effect. These scenarios are so ambitious they don't have to (!) reach net-zero GHG by 2100, shifting median to 2095-2100. #SR15 had net-zero GHG in 2067 #COP27 8/n
During approval of #IPCC WG3 SPM these late (& often missing) net-zero GHG years led to interventions by small island developing states (SIDS) successfully calling for split-up of 1.5C pathways, into those reaching net-zero before 2100 (C1a) and those that don't (C1b) #cop27 9/n
Main argument for splitting up 1.5C pathways (C1a/b): Paris Agreement Art. 4.1 'demands' reaching net-zero GHG by 2100 (here's an article explaining this, maybe notable there's no law scholar co-authoring nature.com/articles/s4324…)
For C1a, net zero GHG is at 2070-2075 #COP27 10/n
Taken together, this creates a paradoxical constellation. #IPCC WG3 C1b pathways don't need to reach net-zero GHG since they're extremely ambitious. C1a pathways do reach net-zero GHG because they have to go net-negative (CO2), since until 2040 they're less ambitious #COP27 11/n
Even #UNFCCC NDC Synthesis Report mentions this. GHG emission reductions 2019-2030 are at 41% for scenarios that reach net-zero GHG pre-2100, and 48% for those that don't. Why would small island developing states (& their advisers) opt for 41%? unfccc.int/ndc-synthesis-… #COP27 12/n
Now back to main recommendation of @UN #HLEGReport on Net-Zero Committments. As we saw, "net zero GHG by 2050 or sooner" isn't backed by IPCC. Same goes for "at least 50% below 2020 levels by 2030". As we saw, #IPCC says 43% 2019-2030 (and 2020 emissions below 2019) #cop27 13/n
Finally, some 'take home' messages
➡️Modelling outputs (e.g. net-zero years) shouldn't be taken at face value, without reflecting underlying assumptions
➡️Even if taken at face value, there's a need to clearly distinguish between net-zero CO2 and net-zero GHG #COP27#HLEG
14/n
Finally, a more general #scipol remark: If an expert group sets benchmarks it can choose whatever it likes. But choosing own benchmarks and then saying these are #IPCC numbers is misleading. This coming from a UN expert body is, quite frankly, a bit disturbing #COP27#HLEG
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As promised, now more on the topics I was deeply involved in as #IPCC#AR6 Synthesis Report author, both in the Summary for Policymakers & the so-called 'Longer Report':
overhoot, net zero, mitigation pathways (incl. CDR)
Let's start with "Overshoot" (B.7), where I was responsible for drafting and 'negotiating' in plenary, but of course not alone (mainly together with @chrisd_jones, with whom I worked on corresponding section 3.3.4 in underlying report) #IPCC#AR6#SYR ipcc.ch/report/ar6/syr/ 2/n
Unfortunately, the UN Secretary General still doesn't understand difference betw net-zero CO2 and much more ambitious net-zero GHG targets. The famous 2050 is net-zero CO2 for 1.5C, net-zero GHG only some decades later, as per #IPCC WG3 & Synthesis Report politico.eu/article/climat…
UN Secretary General has been ill-advised by his own high-level expert group on net-zero, which also confuses net-zero CO2 and net-zero GHG.
After 3 yrs of hard work & a long approval plenary, we got the #IPCC#AR6 Synthesis Report published today, consisting of the Summary for Policymakers and a full report version ➡️ ipcc.ch/report/ar6/syr/
An ongoing 🧵, starting with SPM fig 1 on adverse climate change impacts 1/n
Today we publish the 1st edition of the "State of Carbon Dioxide Removal" report, a global assessment of the current #StateofCDR, and the gap we need to close to achieve the Paris temperature goal.
Full report➡️stateofcdr.org
An ongoing 🧵
[1]
This report compiles a first estimate of the total CDR being deployed (2 GtCO2/yr).
Almost all comes from "conventional" CDR on land, via afforestation, reforestation & forest management.
"Novel" methods don’t contribute much yet. #StateofCDR
[2]
We provide a calculation of total gross CDR in #IPCC-assessed pathways to keep warming below 1.5C and 2C, including all methods. All pathways involve substantial cumulative CDR volumes (450-1100 GtCO2 by 2100) - in addition to immediate & deep emissions reductions #StateofCDR
[3]
➡️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…
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]
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