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Friday, February 28, 2020 - 12:00pm to 1:00pm
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100F Pierce Hall, 29 Oxford St., Cambridge

Atmospheric & Environmental Chemistry Seminar

"The Role of Stratospheric Composition Feedbacks in the Climate Response to Anthropogenic Greenhouse-gas Emissions" with Gabriel Chiodo, Swiss Federal Institute of Technology (IAC-ETH).

The important role of stratospheric feedbacks for the climate system – most notably how the ozone layer responds to anthropogenic forcings (GHGs), and how that response then feeds back on the climate itself – remains largely unexplored, apart from the effects associated with gases regulated by the Montreal Protocol. This is because, to date, most models participating to CMIP inter-comparisons do not account for the complex interplay between stratospheric composition, dynamics and radiation. We here present some recent results illustrating the importance of such interplay in the case of abrupt 4xCO2 experiments from CMIP5. First, we show that increasing carbon dioxide levels lead to substantial changes in the ozone layer, and that the magnitude of these changes is highly model-dependent (Chiodo et al., 2018). Second, we demonstrate how these changes in the ozone layer can have a substantial effect on the circulation response to that forcing in both hemispheres, while barely altering the climate sensitivity (Chiodo & Polvani, 2017; Chiodo et al, 2018). Third, we explore the role of stratospheric water vapor (SWV) in the projected global warming. We quantify the SWV feedback in CMIP5 models, and show that feedbacks arising from stratospheric moistening are on the same order of magnitude as other notoriously important feedbacks, such as surface albedo and cloud feedbacks (Banerjee, et al., 2019). Such findings demonstrate that stratospheric composition changes play a key role in shaping the climate response to anthropogenic forcings, both via radiative and dynamical processes. However, the coupling between ozone, SWV and climate is still subject to large uncertainties. The implications of these results for CMIP6 will be discussed.

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Harvard University
Center for the Environment

Address: 26 Oxford Street, 4th Floor, Cambridge
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