The plausible role of Barents and Kara sea ice loss in driving future polar vortex changes

Friday, March 25th at 9:00-10:00 UTC
All attendees must register through the following link: https://univ-lille-fr.zoom.us/webinar/register/WN_W_HjrR9PQuGZwv1OOdyqRg

Abstract

The Northern Hemisphere stratospheric polar vortex (SPV) is a band of fast blowing eastward winds, forming in winter over the Arctic. The strength of the SPV affects the weather and climate in the densely populated mid-latitudes and is also linked to stratospheric ozone concentrations. Understanding potential changes in the SPV in response to global warming is therefore of huge scientific and societal interest. However, in what way the SPV will respond to global warming is not clear, with climate models disagreeing on the sign and magnitude of projected SPV strength change. Here we address the potential role of Barents and Kara (BK) sea ice loss in this. Using data from 35 different climate models, we show that the SPV weakens as long as sea ice in this region declines but that it strengthens again once all sea ice is gone. However, the time the BK Seas are ice-free differs between models which explains some of the disagreement regarding the polar vortex projections. We quantify the causal effect of BK sea ice loss on the polar vortex and find it to be plausibly very small.  Yet, given the expected dramatic decrease in sea ice in the future, even a small causal effect can explain all of the projected ensemble-mean SPV weakening, approximately one-half of the ensemble spread in the middle of the 21st century, and one-third of the spread at the end of the century. Finally, we note that most models have unrealistic amounts of BK sea ice, meaning that their SPV response to ice loss is unrealistic. Bias adjusting for this effect leads to pronounced differences in SPV response of individual models at both ends of the spectrum. Overall, our results indicate the importance of exploring all plausible implications of a changing Arctic for regional climate risk assessments.

Dr. Marlene Kretschmer is a research scientist at the University of Reading, UK. Currently she holds an individual Marie Curie fellowship to apply causal inference methods to evaluate the representation of large-scale drivers (such as the stratospheric polar vortex) of European precipitation in climate models. She is an expert in using these novel statistical methods as well as other machine learning algorithms to identify and quantify causal pathways of teleconnections from climate data.

Knowns and unknowns on the impacts of COVID-19 lockdowns on urban air quality: A glimpse into what the future may hold

Tuesday, November 23rd at 9:00-10:00 UTC
All attendees must register through the following link: https://univ-lille-fr.zoom.us/webinar/register/WN_W_HjrR9PQuGZwv1OOdyqRg

Abstract

The coronavirus-19 pandemic led to government interventions to limit the spread of the disease that are unprecedented in the last decades. Stay at home orders led to sudden decreases in atmospheric emissions, most visibly from the transportation sector. In this seminar we summarize the current knowledge of the influence of these emission reductions on atmospheric composition and air quality. We show how key air pollutants change as lockdown measures become more severe. This includes anthropogenic pollutants directly emitted to the atmosphere called primary, as well as pollutants formed through atmospheric chemistry, called secondary.

Despite the overall emission reductions during the lockdown measures secondary pollutant concentrations that impact human health, including ozone and particulate matter, either increased or exceeded the world health organization guidelines. We highlight which anthropogenic pollution sources can play a key role in successfully mitigating secondary pollution to improve future urban air quality. Furthermore, we emphasize the need for future studies to address the seasonality of emission reductions during these lockdowns. Finally, we promote our online database available in https://covid-aqs.fz-juelich.de. This website is designed as a living version of our work and as new literature emerges authors of published papers are encouraged to upload their data to the database, thus complementing the data coverage in space, time, and compound dimensions.

Dr. Georgios Gkatzelis received a Ph. D. in physical chemistry with Professor Astrid Kiendler-Scharr at the University of Cologne. He moved to NOAA, USA in 2018 as a post-doctoral researcher working with Dr. Carsten Warneke and since August, 2020 is a research scientist at Research Center Jülich, Germany. His major research has been on the emissions, chemical evolution and impacts of volatile organic compounds (VOCs) to secondary organic aerosol (SOA) formation in the Earth’s atmosphere. His research background includes multiple chamber and field studies in Europe, China, and the US. Specifically, he measures VOCs using start-of-the-art mass spectrometers that he deploys on ground site, mobile laboratory and aircraft platforms in order to identify, and quantify VOC emissions and their potential to form SOA. More recently his focus has been on emerging urban pollution sources, more specifically volatile chemical product emissions in urban environments and their emission strength compared to traditional sources as for example traffic.