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Investigating two-way linkages between mid-latitude air pollution and Arctic climate change

Dr Steve Arnold (SEE), Dr Juliane Schwendike (SEE)

Contact email: s.arnold@leeds.ac.uk

Background

Observations show that the Arctic has warmed more than twice as rapidly as the global average over the past few decades (Trenberth et al., 2007), resulting in large changes in the Arctic climate system, most notably substantial reductions in summer sea ice extent. In addition to the warming effects of global increases in atmospheric CO2 concentrations, Arctic surface temperatures have been shown to be particularly sensitive to the atmospheric radiative effects of so-called short-lived climate pollutants (SLCPs), which include aerosols (such as sulfate, nitrate, and black carbon (BC) particulate matter) and the short-lived greenhouse gas tropospheric ozone (O3). SLCPs have sources within the Arctic from activities such as fossil fuel extraction, domestic fuel combustion and shipping, but are also transported efficiently to high latitudes by weather systems from sources in Europe, N America and Asia (Law et al., 2014; Stohl, 2006; see Fig. 1). In addition to the direct effects of SLCPs in the Arctic, Arctic temperatures also respond to their effects outside of the Arctic region, via transport of heat from lower to high latitudes (Shindell and Faluvegi, 2009). Due to this effect, several studies have shown that the Arctic surface temperature response to radiative forcing by changes in SLCP abundances at mid-latitudes has likely been larger than that due to SLCP changes locally in the Arctic (Sand et al., 2013; Acosta Navarro, 2016; see Fig. 2). A key determinant of the climatic effect of SLCPs in the atmosphere is their vertical profile distribution, which is largely determined by large-scale uplift and export of pollution within frontal systems. However, models have been shown to perform badly in reproducing the vertical distributions of aerosol and trace gases, particularly at high latitudes (Emmons et al., 2015; Arnold et al., 2015). This results in low confidence in our ability to diagnose contributions from SLCPs from different source regions and sectors to Arctic warming and sea ice change.

In addition to SLCPs having important effects on Arctic surface temperatures, some studies have postulated a link between Arctic warming and changes in mid-latitude weather patterns. Since aerosol particulates and tropospheric ozone are both harmful to human health, the response of their abundances to such changes in weather patterns and circulation may be important for air quality. Recently, Zou et al., (2017) identified a link between changes in Arctic sea ice cover, high latitude snow and intensification of winter time pollution episodes in Eastern China, resulting from changes in flow patterns over East Asia associated with venting of pollution away from the continental surface. However, the robustness of such relationships and their relevance to other mid-latitude regions are yet to be determined.

Fig 1: Continental export of aerosol pollution haze from eastern China into the East China Sea and Pacific Ocean (NASA).

Aims and approach

In this project, you will use a hierarchy of models (Lagrangian transport model, regional atmospheric model, global Earth system model) alongside observations of atmospheric composition from aircraft, satellite and surface stations to improve understanding of 2-way linkages between SLCP abundances at mid-latitudes and Arctic climate. The overarching aims of the project are to investigate and evaluate: 1) simulation of SLCP continental export and resultant radiative forcing at mid-latitudes, and impacts on Arctic surface temperature response, and 2) implications of Arctic climate change on mid-latitude air quality through atmospheric circulation changes.

Specific objectives of the research project may include:

  1. Evaluation of SLCP export from the mid-latitude continents facilitated by frontal weather systems in regional and global models, through comparison with aircraft and satellite data.
  2. Investigating sensitivities of simulated SLCP export to key model chemical and physical processes.
  3. Investigating sensitivity of magnitude and spatial pattern of Arctic climate response to different simulated SLCP forcing scenarios.
  4. Identifying dominant patterns and modes of variability in Arctic climate associated with variability in mid-latitude winter-time air pollution enhancements.
  5. Determining the sensitivity of mid-latitude air quality to northern hemisphere circulation changes induced by Arctic warming and sea ice loss using idealized climate model simulations.
  6. Investigating the balance between cooling and warming SLCP influences on Arctic climate and the sensitivity of this balance to different emission sources, atmospheric transport and chemistry processes.

Fig 2: Contributions to Arctic surface temperature change from different SLCPs and source regions within and outside the Arctic (AMAP, 2015).

Potential for high impact outcome

This project will deliver improved estimates of the climate benefits that can be expected from regional and sector-based emission reductions, and linkages between rapid Arctic change and the mid-latitudes, which are of high interest to policy makers, and are key priorities of the International Arctic Science Committee (iasc.info). The work undertaken by the student will contribute new international assessment within the Arctic Monitoring and Assessment Programme (AMAP) Expert Group on Short-lived Climate Forcers in the Arctic, as well as onging work within the international PACES (air Pollution in the Arctic: Climate, Environment and Societies) Project Working Group 1 (http://pacesproject.org/) ensuring effective dissemination to the wider scientific and policy-facing communities.

Training and research group

The student will benefit from expertise in both numerical atmospheric chemistry-climate modelling and analysis of large geophysical datasets. The project provides a high level of specialist scientific training in: (i) State-of-the-science application and analysis of global atmospheric models, (ii) analysis and interpretation of in-situ aircraft datasets and satellite datasets, (iii) numerical modeling and use of supercomputers, (iv) science communication with expert and non-expert groups through attendance at international workshops on SLCP research and impacts. The student will benefit from closely collaborating with internationally leading groups from Europe, the US and Asia, and from attending workshops and meetings to work alongside international experts in atmospheric chemistry and climate.

The student will join a group of around 8 students and postdoctoral researchers working on projects in atmospheric composition and its links to climate, air quality and the biosphere. For more information about our research and recent publications, see: http://homepages.see.leeds.ac.uk/~lecsra. We encourage interested applicants to get in touch and arrange an informal visit to Leeds to meet and talk informally with the group.

Partners and Collaborations

The project is closely related to ongoing efforts in the new international PACES initiative. The student will be expected to travel to and contribute to scientific meetings as part of PACES and AMAP assessments.

Further information

AMAP Assessment 2015: Black carbon and ozone as Arctic climate forcers

UNEP Integrated Assessment of Black Carbon and Tropospheric Ozone (summary)

AMAP Report on The Impact of Black Carbon on Climate

POLARCAT project on Arctic climate and air pollution

References

Acosta Navarro, J. C., et al., (2016), Amplification of Arctic warming by past air pollution reductions in Europe, Nature Geoscience, 9, 277–281, doi:10.1038/ngeo2673.

Arnold, S. R., Emmons, L. K., Monks, S. A., Law, K. S., Ridley, D. A., Turquety, S., Tilmes, S., Thomas, J. L., Bouarar, I., Flemming, J., Huijnen, V., Mao, J., Duncan, B. N., Steenrod, S., Yoshida, Y., Langner, J., and Long, Y., (2015), Biomass burning influence on high-latitude tropospheric ozone and reactive nitrogen in summer 2008: a multi-model analysis based on POLMIP simulations, Atmos. Chem. Phys., 15, 6047-6068, doi:10.5194/acp-15-6047-2015.

Emmons, L. K., Arnold, S. R., Monks, S. A., Huijnen, V., Tilmes, S., Law, K. S., Thomas, J. L., Raut, J.-C., Bouarar, I., Turquety, S., Long, Y., Duncan, B., Steenrod, S., Strode, S., Flemming, J., Mao, J., Langner, J., Thompson, A. M., Tarasick, D., Apel, E. C., Blake, D. R., Cohen, R. C., Dibb, J., Diskin, G. S., Fried, A., Hall, S. R., Huey, L. G., Weinheimer, A. J., Wisthaler, A., Mikoviny, T., Nowak, J., Peischl, J., Roberts, J. M., Ryerson, T., Warneke, C., and Helmig, D., (2015), The POLARCAT Model Intercomparison Project (POLMIP): overview and evaluation with observations, Atmos. Chem. Phys., 15, 6721-6744, doi:10.5194/acp-15-6721-2015.

Law, K. S., Stohl, A., Quinn, P. K., Brock, C., Burkhart, J., Paris, J.-D., Ancellet, G., Singh, H. B., Roiger, A., Schlager, H., Dibb, J., Jacob, D. J., Arnold, S. R., Pelon, J., and Thomas, J. L., (2014), Arctic Air Pollution: New Insights from POLARCAT-IPY, Bull. Amer. Meteor. Soc., 95, 1873-1895, doi:10.1175/BAMS-D-13-00017.1

Sand, M. et al. (2015), Response of Arctic temperature to changes in emissions of short-lived climate forcers, Nature Clim. Change, doi:10.1038/nclimate2880.

Shindell, D.T., and G. Faluvegi, (2009), Climate response to regional radiative forcing during the twentieth century, Nature Geoscience 2, 294-300.

Stohl, A. (2006), Characteristics of atmospheric transport into the Arctic troposphere, J. Geophys. Res., 111, D11306, doi:10.1029/2005JD006888.

Trenberth, K.E., et al., (2007), Observations: Surface and Atmospheric Climate Change. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Y. Zou, Y. Wang, Y. Zhang, J.-H. Koo, (2017), Arctic sea ice, Eurasia snow, and extreme winter haze in China. Sci. Adv. 3, e1602751.

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