Joint Seminar: Quantifying and comparing effects of climate engineering methods on the Earth system

Climate engineering (CE) methods are much discussed tools to complement mitigation efforts aiming at stabilizing future temperatures. Previous model studies on potential impacts of CE have focused mainly on effects of individual CE methods as simulated by different models. Here we assess atmosphere-, ocean-, and land-based CE measures with respect to effects and side effects consistently within one comprehensive model. We use the Max Planck Institute Earth System Model (MPI-ESM) with prognostic carbon cycle to compare solar radiation management (SRM) by stratospheric sulfur injection with carbon dioxide removal methods: afforestation and ocean alkalinization. For each of the three CE methods we perform simulations forced by fossil-fuel CO2 emissions according to the Representative Concentration Pathway (RCP) 8.5. We show that the CE methods differ vastly in terms of their effects on different Earth system components. We find that mitigating feedbacks emerge: for example, as a response to SRM temperatures are reduced leading to a reduction of atmospheric CO2 due to enhanced land carbon uptake. In addition, unintended side effects become clear: for example, terrestrial net primary production (NPP) is substantially reduced in the alkalinization scenario, whereas SRM has almost no net effect on terrestrial NPP due to counteracting effects of decreased water stress in low latitudes and weaker boreal forest expansion. We also identify challenges arising in a comparative assessment of different CE methods: the quantitative results depend on details of the CE scenarios and on the underlying models, and an interpretation of relative efficiency depends on the choice of variables that are analyzed. Furthermore, we show that normalisations allow for a better comparability of different CE methods. For example, we find that despite different amounts of global surface cooling achieved, local amplification factors compared to the global mean temperature changes are generally similar in the CE scenarios, with the exception of Arctic amplification, which is strengthened by SRM. In addition, we find a higher efficiency to remove carbon from the atmosphere for alkalinization compared to afforestation, again illustrating how carbon cycle feedbacks in the coupled Earth system alter the mitigation potential of CE methods. Overall, our study shows how different CE methods affect the components of the Earth system and why a comparative assessment of CE is difficult.

Datum

23.05.2017

Uhrzeit

15:15 Uhr

Ort

Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg

ReferentIn

Sebastian Sonntag, MPI-M

Chair

Guidi Zhou
Karsten Peters

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