Modelling the effects of realistic polar stratospheric clouds on past climate and future ozone

Lead Research Organisation: NERC British Antarctic Survey
Department Name: Science Programmes


Climate change and its attribution to human activity is the most important global environmental challenge of the 21st Century. Stratospheric ozone depletion due to reactive chlorine from CFCs was one of the most important of the 20th Century. Any unexplained climate change would lead to severe loss of confidence in science-based advice when priorities for implementing the Kyoto Protocol or its successors are being debated. Any unexplained delay in the recovery of ozone depletion, expected because of the Montreal Protocol, could lead to similar loss of confidence by opinion formers and policy makers. Here we propose to investigate a large unexplained change in Antarctic climate and a strong possibility of delayed recovery of the Antarctic ozone hole, and proffer explanations. The largest warming observed in the troposphere in the last 30 years occurred in the mid- troposphere in Antarctic winter. This recent discovery cannot yet be explained - computer modelling with increased greenhouse gases shows too small a warming - but recent work has implicated increased Polar Stratospheric Clouds (PSCs). We propose to test the hypothesis that a combination of increased greenhouse gases and increased PSCs has caused the warming. We would conduct a thorough modelling study, after inserting a comprehensive PSC growth scheme, and an improved calculation of the stratospheric cold points induced by atmospheric waves above mountains, into the premier UK atmospheric model. The improved model will also be used to forecast the future evolution of the ozone hole. During the 21st Century, CFCs are expected to reduce. But greenhouse gases will continue to increase, which will act to cool the stratosphere and so produce more PSCs. This latter process may significantly delay the expected recovery of the ozone hole. This proposal combines world leaders in PSC and atmospheric chemistry modelling at Leeds and Cambridge Universities with BAS expertise in Antarctic climate attribution and publicity, to create an exceptionally strong team. This work should be done now before the unexplained change in Antarctic climate comes to the attention of the wider media and public.
Description This work is focused on improved representation of polar stratospheric clouds (PSCs) in the chemistry-climate version of the UK Met Office's internationally renowned Unified Model, by including simulation of PSCs induced by the temperature fluctuations caused by mountain waves. This formation mechanism is missing in standard chemistry-climate models because these temperature fluctuations are typically neither resolved nor parameterised, i.e. resulting in a significant underestimation of stratospheric ozone.

In this research we inserted a mountain wave parameterisation which computes the temperature fluctuations due to unresolved (sub-grid scale) mountain waves into a chemistry-climate model. The subsequent wave-induced 'cooling phase' computed by the scheme (which is an important source of PSCs) was passed to the PSC scheme of the model, and caused a 30-50% increase in PSCs over the Antarctic Peninsula compared to a control run.

The high sensitivity of the model to this change suggests that such improvements are of the utmost importance in enabling realistic modelling of the recovery of the Antarctic ozone hole, and the attendant impacts this would have on the Southern Hemisphere climate.
Exploitation Route The findings are applicable to all global chemistry-climate models ran by major research institutes. The findings and methodologies developed could be used to improve their chemistry-climate models and in doing so result in better future projections of the timing of the closure of the Antarctic ozone hole.
Sectors Environment

Description The findings were briefed to the Department of Environment, Food, and Rural Affairs (DEFRA).
Sector Environment
Impact Types Societal

Description Invited seminar
Amount £500 (GBP)
Organisation Julich Research Centre 
Sector Public
Country Germany
Start 05/2014 
End 05/2014
Title mountain wave parameterisation 
Description Parameterisation of the temperature fluctuations induced by mountain waves, I.e. the temperature fluctuations produced by unresolved waves. 
Type Of Material Computer model/algorithm 
Provided To Others? No  
Impact It has been inserted into the UKCA chemistry-climate model where it has been used to more realistically represent mountain wave-induced polar stratospheric clouds (PSCs). 
Description Julich Research Centre 
Organisation Julich Research Centre
Country Germany 
Sector Public 
PI Contribution Andrew Orr and Scott Hosking are working on a study to further improve the representation of mountain wave-induced polar stratospheric clouds (PSCs) in the UKCA chemistry-climate model. To this end we are examining the sensitivity of the model representation of PSCs to e.g. the mountain wave parameterisation developed in Orr et al. (2014) by comparison with long term PSC and mountain wave observations.
Collaborator Contribution Reinhold Spang and Lars Hoffmann will provide the long term mountain wave observations based on MIPAS and AIRS satellite sensors, respectively.
Impact A ten-year Antarctic PSC climatology, derived from MIPAS, has been developed.
Start Year 2014
Description Karlsrule Institute of Technology (KIT) 
Organisation Karlsruhe Research Centre
Country Germany 
Sector Academic/University 
PI Contribution I submitted a proposal for a PhD to the Cambridge DTP on 'Future startospheric ozone changes and associated climate impacts'. Prof Peter Braesicke from KIT, was one of the co-supervisors. He is doing related research in Germany, and we discussed that the collaboration would be mutually beneficial.
Collaborator Contribution Prof Peter Braesicke invited me to KIT in 2016 to discuss our shared research interests.
Impact A PhD proposal to the Cambridge DTP on 'Future startospheric ozone changes and associated climate impacts' was submitted for the 2018 intake round.
Start Year 2014
Description DEFRA 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact Briefed representativeness from the Department of Environment, Food, and Rural Affairs (DEFRA) on the importance and outcomes of the grant proposal.

The DEFRA participants were very interested and promised to include the outcomes in an upcoming report.
Year(s) Of Engagement Activity 2014
Description Expert reviewer for Chapter 5 of the WMO 2018 Ozone Assessment Report 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I was invited to provide comments on Chapter 5 of the WMO Ozone Assessment Report, 2018.
Year(s) Of Engagement Activity 2018
Description School talks on the Antarctic ozone hole 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Each year I give a number of talks to secondary schools on the Antarctic ozone hole, and more generally climate change.
Year(s) Of Engagement Activity 2014,2015,2016,2017,2018