Comparative assessment of potential impacts, side-effects and uncertainties of CE measures and emission-reduction efforts (ComparCE-2)
Atmospheric Science
Economic Theory
Final Report Abstract
Climate Engineering (CE) as an option to prevent dangerous climate change has reached the political debate. For a well-informed societal decision on potential future deployment, CE research towards a comprehensive assessment is needed. A main task of ComparCE was to use numerical models to assess CE methods in a coherent model context. The selection of suitable models and indicators, the quantification of model uncertainties, as well as the identification of policy-relevant metrics were some of the major challenges addressed by the ComparCE project as a contribution to the overall goals of the Priority Program (SPP 1689). To study the theoretical potentials and side effects of single CE options, initially idealized and maximum-capacity simulations were performed with a model of intermediate complexity. A key finding in this context, was the fact that whenever a method was found to be efficient in terms of mitigating climate change, there was a substantial termination risk associated with it, with the notable exception of Ocean Alkalinization. Three of the previously assessed CE options were selected for a comparative assessment in a state-of-the-art Earth system model. In order to monitor individual CE measures, the detectability of CE signals needs to be ensured as well as the ability to attribute these signals to their causes. One advantage for detecting these engineered signals in the climate system is that the start date of the additional external forcing is well known. For the first time, single-model estimates of the externally forced response were used to detect the CE signal against climate noise. The results suggest that for a combination of smallscale measures, detecting individual contributions may be very difficult at least. Beyond that, it was found that climate feedbacks play important roles in determining the potential of CE options, and that a normalization is helpful to allow for a fair comparison of potentials and side effects. However, challenges arising from a CE comparison were identified, which then contributed to developing a framework for a comparative assessment of CE. Research on individual CE methods is often biased by disciplinary expertise. The application of limited ad-hoc indicator sets is no longer valid when large scale perturbations of the climate system are concerned. ComparCE developed a method that allows for the identification of policy-relevant indicators and the construction of a decision-informing metric, which is highly recommended to take an iterative approach that includes stakeholder dialogue, in order to include relevant information regarding the respective value systems.
Publications
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(2014): Potential climate engineering effectiveness and side effects during a high carbon dioxide-emission scenario. Nature Communications, 5, 3304
Keller, D. P., Feng, E. Y. & Oschlies, A.
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(2016). Impacts of artificial ocean alkalinization on the carbon cycle and climate in Earth system simulations. Geophysical Research Letters, 43, 6493–6502
Ferrer-González, M. F., & Ilyina, T.
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(2017), Indicators and metrics for the assessment of climate engineering, Earth’s Future, 5, 49–58
Oschlies, A., H. Held, D. Keller, K. Keller, N. Mengis, M. Quaas, W. Rickels, and H. Schmidt
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(2018). Enhanced rates of regional warming and ocean acidification after termination of large-scale ocean alkalinization. Geophysical Research Letters, 45, 7120-7129
Ferrer-Gonzalez, M., Ilyina, T., Sonntag, S. & Schmidt, H.
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(2018). Evaluating climate geoengineering proposals in the context of the Paris Agreement temperature goals. Nature Communications, 9 (1), 1–19
Lawrence, M. G., Schäfer, S., Muri, H., Scott, V., Oschlies, A., Vaughan, N. E., et al.
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(2018). Quantifying and comparing effects of climate engineering methods on the Earth system. Earth’s Future, 6(2), 149-168
Sonntag, S., Ferrer González, M., Ilyina, T., Kracher, D., Nabel, J. E., Niemeier, U., Pongratz, J., Reick, C. H. & Schmidt, H.
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(2018). Systematic Correlation Matrix Evaluation (ScoMaE)–a bottom–up, science-led approach to identifying indicators. Earth System Dynamics, 9(1), 15-31
Mengis, N., Keller, D. P., & Oschlies, A.
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(2019). Climate engineering– induced changes in correlations between Earth system variables—implications for appropriate indicator selection. Climatic Change, 153(3), 305-322
Mengis, N., Keller, D. P., Rickels, W., Quaas, M., & Oschlies, A.
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(2020). Comparative assessment of climate engineering scenarios in the presence of parametric uncertainty. Journal of Advances in Modeling Earth Systems, 12, e2019MS001787
Tran, G. T., Oschlies, A., & Keller, D. P.
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(2020). Detectability of artificial ocean alkalinization and stratospheric aerosol injection in MPI-ESM. Earth’s Future
Fröb, F., Sonntag, S., Pongratz, J., Schmidt, H., & Ilyina, T.
