Monday, October 5, 2020

Reappraisal of the climate impacts of ozone‐depleting substances

Olaf Morgenstern, Fiona M. O'Connor, Ben T. Johnson, Guang Zeng, Jane P. Mulcahy, Jonny Williams, João Teixeira, Martine Michou …First published: 28 September 2020
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL088295

Added by CC from https://scied.ucar.edu/ozone-layer, 

Abstract

We assess the effective radiative forcing due to ozone‐depleting substances using models participating in the Aerosols and Chemistry and Radiative Forcing Model Intercomparison Projects (AerChemMIP, RFMIP). 
A large inter‐model spread in this globally averaged quantity necessitates an ``emergent constraint" approach whereby we link the radiative forcing to ozone declines measured and simulated during 1979‐2000, excluding two volcanically perturbed periods. 

During this period ozone‐depleting substances were increasing, and several merged satellite‐based climatologies document the ensuing decline of total‐column ozone.

Using these analyses we find an effective radiative forcing of ‐0.05 to 0.13 Wm‐2. Our best estimate (0.04 Wm‐2) is on the edge of the ``likely" range given by the 5th Assessment Report of IPCC of 0.03 to 0.33 Wm‐2, but is in better agreement} with two other literature results.

Plain Language Summary

Chloroflourocarbons and other compounds involved in ozone depletion are also powerful greenhouse gases, but their contribution to global warming is reduced due to the cooling effect of the ozone loss which they induce.
Models informing an upcoming climate report disagree on the ozone loss and thus on the climate influence of these gases. Here we use observed ozone loss to reduce the resultant uncertainty in their overall climate influence and infer a larger cooling. 
Here we use observed ozone loss to reduce the resultant uncertainty in their overall climate influence and infer a smaller warming influence of these substances than was considered likely in a 2013 climate report. 

The result implies a smaller benefit to climate due to their phase‐out, mandated under the Montreal Protocol, than would have been the case under previous understanding.


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