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WP6 brief overview and �4-year summary

Jörg Schwinger, Laurent Bopp, and WP6 partners

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Financial crisis 2008

COVID 19

Paris agreement 2015

No sign of globally sustained emission reductions

Emissions over the recent past are not consistent with reaching the 1.5° or 2° target

Global Carbon budget 2022, Friedlingstein et al.

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Hausfather and Peters (2020)

But we are NOT on a path to a “worst case” future, either

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Therefore, plausible 1.5° scenarios all contain carbon dioxide removal (CDR)

IPCC SR15, Fig. SMP3b

Even in the most optimistic scenarios, reaching net-zero emissions involves carbon dioxide removal (CDR) from the atmosphere (at least to compensate for hard-to-abate emissions)

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WP6 has been working on

provision of Earth system model scenarios

robustness of ESM projections w.r.t. mitigation targets

mitigation pathways towards zero emissions and pathways with negative emissions

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provision of Earth system model scenarios

Kwiastkowsky et al. 2020

The triple thread projected by CMIP6 ESMs

warming acidification deoxygenation

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Bourgeois et al., D6.2

Comparing high, low, and overshoot scenarios:

For ambitious mitigation targets, there is little difference between scenarios (many targets are exceeded early on)

constraining ESMs, and robustness w.r.t. mitigation targets

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constraining ESMs, and robustness w.r.t. mitigation targets

Summary and synthesis available in D6.3

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Trends in seasonal amplitudes of surface ocean pCO2 in simulations with/without anthropogenic forcing versus 6 observational products (Fay et al.,2021)
Analysis of Covariance: observed trends in mid-latitude regions firmly attributed to anthropogenic forcing (no trends in tropics+SO in obs. and models)
Large data-model discrepancies in the mean pCO₂ seasonal cycle in high-latitudes
Considerable differences in observational products, questioning their reliability (e.g., for decadal trend reconstructions)

Joos, Hameau, Frölicher, Stephenson., GRL, subm.

The growing seasonal amplitude of pCO₂

Historical�(anth+solar+volc)

Natural

(solar+volc.)

SeaFlux Data

constraining ESMs, and robustness w.r.t. mitigation targets

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zero emissions

positive emissions

Idealized simulations with NorESM2…

Schwinger et al. 2022

Mitigation pathways towards zero emissions and pathways with negative emissions

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Mitigation pathways towards zero emissions and pathways with negative emissions

Idealized simulations with NorESM2, show large temperature fluctuations (related to AMOC decrease and recovery) north of 40N after emissions have been phased out

emissions phased out

>2 °C

Schwinger et al. 2022

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Reversibility in mitigation pathways with negative emissions

Roy et al. under preparation, D6.4

See also my presentation after �this overview talk

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Berger et al. 2023, D6.4

Simulating efficiency of macroalgae cultivation in EEZs

Mitigation pathways with negative emissions

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Mitigation pathways with negative emissions

Simulation of Ocean Alkalinization scenarios developed in WP5 with NorESM and IPSL ESMs

Atmospheric CO₂ about 25 ppm lower after 75 years of alkalinization through addition of 5 Pg of Ca(OH)₂per year

D6.4

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We developed a new adaptive emissions reduction approach that allows to reach any temperature target following a smooth emissions pathway

References:

Terhaar, J., Frölicher, T. L., et al. Adaptive emission reduction approach to reach any global warming target. Nature Climate Change 12, 1136-1142 (2022)

Terhaar, J., Frölicher, T. L., Joos, F., Ocean acidification in emission-driven temperature stabilization scenarios: the role of TCRE and non-CO₂ greenhouse gases. Environmental Research Letters 18, 024033 (2023)

New method for simulating mitigation pathways in ESMs

See presentation by Thomas Frölicher

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WP6 status in terms of Deliverables:
D6.1: Additional high frequency ESM output (Submitted M6; NORCE responsible, UBERN, AWI, MPI-M, MF-CNRM, SMHI, ENS) D6.2: Report on robustness of ESM simulations and uncertainties with respect to thresholds defined by the impact metrics developed in WP5. (M30; ENS responsible, NORCE, UBERN, UiB) D6.3: Report on constraining the CMIP6 model ensemble and appropriate model weighting schemes. (M38; ENS, NORCE responsible, UBERN, UiB) D6.4: Run selected mitigation scenarios in ESMs, synthesis report on ESM projections with and without mitigation pathways (M44; NORCE responsible, GEOMAR, MPI-M, ENS, MF-CNRM, UBERN, AWI) D6.5: Publication draft on pathways for avoiding ocean biogeochemical damage: Mitigation targets, mitigation options, and projections. (M45; all partners from WPs 5&6, UBERN responsible)

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Aspects to be discussed in the WP breakout session

upcoming deliverables:

D6.4: Run selected mitigation scenarios in ESMs, synthesis report on ESM projections with and without mitigation pathways (M44)

D6.5: Publication draft on pathways for avoiding ocean biogeochemical damage: Mitigation targets, mitigation options, and projections. (M45; all partners from WPs 5&6, UBERN responsible)

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Lessons learned…

interactions with WPs 1-4 could have been established better

… and knowledge gaps

we need to learn more about the physical and biogeochemical response to phasing out emissions (and to negative emissions)
need to explore the Earth system effectiveness, feedbacks, and side effects of negative emission options

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Key messages

Emission trajectories over the past years are not consistent with reaching the 1.5° or 2° target

Carbon dioxide removal (CDR) cannot replace fast and immediate emission reductions in any way – too expensive, too many side effects, too little removal capacity, too risky to bet on

Reaching net-zero emissions will involve carbon dioxide removal (CDR) from the atmosphere - at a minimum to compensate for hard-to-abate emissions, maybe also to lower temperatures after an overshoot. We will need more knowledge about CDR options.

Overshoot pathways generally come with an additional risk

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Thank you for listening

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 820989. The work reflects only the author’s/authors’ view; the European Commission and their executive agency are not responsible for any use that may be made of the information the work contains.

COMFORT annual meeting 2023, Bergen