COMFORT GA 2023

Thomas Frölicher

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Climate and Environmental Physics

Oeschger Centre for Climate Change Research

University of Bern, Switzerland

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@froeltho

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Thanks to: Jens Terhaar, Mathias Aschwanden, Pierre Friedlingstein, Fortunat Joos

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The adaptive emissions reduction approach and its applications

Projections by Earth system models and REB estimates are uncertain

+47% since 1750

Idea: Adaptive approach to successively quantify the global emissions reductions that allow reaching any temperature target, solely based on observations and not on climate model projections

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large uncertainty

large uncertainty

Figure SPM.10 (IPCC WGI, 2021)

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Terhaar et al. (Nature Climate Change, 2022)

The adaptive emissions reduction approach (AERA)

Idea: Adapting emissions successively like a control system with feedback loop

repeat at each stocktake

Observations:

• Global temperature
• Radiative forcing
• Emissions data

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At each stocktake, future CO₂-fe emissions can be split into contribution from CO₂, CH₄, N₂O, etc.

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Two earlier approaches for temperature stabilization: Zickfeld et al. (2009,2013), Goodwin et al. (2018)

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Stocktake frequency

Testing AERA with the Bern3D-LPX climate model

> 1’000 sensitivity simulations with the Bern3D-LPX

equilibrium climate sensitivities (1.9 – 5.7°C)

varying strengths of the ocean carbon sink

radiative forcing estimates

deviations between emissions reductions quantified by the AERA versus those implemented

different metrics to split CO₂ equivalent emissions into CH₄, N₂O, etc.

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Testing AERA with the Bern3D-LPX climate model

• Any temperature target can be reached following a smooth emissions pathways

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• It’s adaptive nature makes AREA robust against uncertainties in observational records, climate sensitivity, effectiveness of emissions reduction implementations and metrics to estimate CO₂ emissions

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Terhaar et al. (Nature Climate Change, 2022)

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Testing AERA with the Bern3D-LPX climate model

• For the fixed 1.5°C target, CO₂-fe emissions need to reach zero CO₂-fe emissions by approximately 2038 and peak afterwards at negative emissions of -2.7 Pg C yr^-1

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• For the fixed 2.0°C target, the resulting CO₂-fe emissions curves reach zero emission by approximately 2070 and peak afterwards at negative emissions of -0.4 Pg C yr^-1

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• Overshoot case demonstrates that AERA also works for moving temperature target

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+156% since 1750

Application 1: The role of non-CO₂ greenhouse gases for ocean acidification in a stabilized 1.5°C world

high CO₂ / low non-CO₂

low CO₂ / high non-CO₂

Terhaar et al. (Environmental Research Letters, 2023)

• The choice of emissions reduction between CO₂ and non-CO₂ emission is important for future ocean acidification

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• Low reduction in non-CO₂ GHGs emissions necessitate strong reduction in CO₂ emissions and lead to relatively little ocean acidification

Temperature anomaly (°C)

CO₂ emissions (Pg C yr^-1)

Global surface ocean pH

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+156% since 1750

Application 2: AERA-MIP

• AERA successfully applied to 12 Earth system models (9 full ESMs, 3 EMICs)
• Analysis of carbon budget and impacts at stabilized warming levels

Temperature anomaly (°C)

CO₂-fe emissions (Pg C yr^-1)

Atmospheric CO₂

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Silvy et al. (in prep.)

Summary

AERA is a new policy tool for calculating emissions reductions to meet any temperature target, only based on observations.

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AERA is a new tool that guides model simulations to stabilize climate at any chosen temperature target. AERA-MIP simulations are directly comparable in terms of impacts under equal warming.

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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)

Silvy, Y., et al. Emissions pathways compatible with 1.5°C and 2°C stabilized warming in fully coupled Earth system models: first results from AERA-MIP. EGU Poster EGU23-6073

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Questions?

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This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 820989 (project COMFORT, Our common future ocean in the Earth system – quantifying coupled cycles of carbon, oxygen, and nutrients for determining and achieving safe operating spaces with respect to tipping points). 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.