Nathanael Harwood

Nathanael Harwood

Profile Display Name:

Nathanael Harwood

E-mail Address:

Start Year

2015 (Cohort 2)

Research interests:

Climate science, Arctic, North Atlantic, Atmospheric Circulation, Teleconnections, Machine Learning.

Hobbies and interests:

PhD Project
PhD Title

Using Bayesian Networks to investigate the role of Arctic change in the rise of extreme weather at mid-latitudes

Research Theme

Past Life and Environments

Primary Supervisor
Primary Institution


Secondary Supervisor
Secondary Institution


Additional supervisor(s)

Allan Tucker (Brunel University London),
Richard Hall (University of Lincoln (now University of Bristol)),


The Arctic is warming at 2-3 times the rate of the rest of the Northern Hemisphere, with rapid loss of sea ice occurring at an accelerating rate. Recent research has put forward the idea that rapid changes in the Arctic are contributing to extreme weather patterns at midlatitudes via an increase in the waviness of circulation and thus extreme weather frequency. Methods used to test this theory vary greatly and often do not include multiple potential drivers in observational approaches. This work constructs climate networks using network structures which are determined from the data using a machine learning approach called dynamic Bayesian networks. With tropical regions of importance included alongside potential Arctic drivers, the resulting structures reveal that the Arctic and midlatitude regions exhibit a strong co-dependency which shows that wavier circulation patterns play an important part in driving observed amplified warming in the Arctic as well as being a response to it on timescales of up to a month. The importance of the bidirectional nature of this relationship has been underplayed in the scientific literature surrounding the research area, as well as in the reporting and public knowledge. Finally, network results show that periodic shifts to slow-flow conditions in stratospheric circulation may have the strongest influence on the patterns of the jet stream on monthly timescales.

Policy Impact

The relative importance of the Arctic in driving midlatitude circulation anomalies remains unresolved, but this work has contributed more evidence to the theory that coupling of Arctic warming and midlatitude circulation is an important feedback mechanism even in the face of tropical forcing, stratospheric inputs and internal variability in midlatitude circulation. This is of interest to climate scientists working on future climate projections who need to model such feedbacks effectively, and to seasonal forecasters looking to drive up forecast skill who may have underweighted this feedback relationship due to the lack of a robust causal connection (in the Arctic-to-midlatitude direction) in atmospheric modelling studies. On the flip side, it is important that policy specialists be aware that simple claims about the impact of the Arctic on extreme weather need to be seated in a more advanced understanding of atmospheric circulation. Currently, claims about the ‘polar vortex’ and direct, causally-driven linkages to Arctic warming dominate the scientific reporting and policy landscape surrounding extreme weather (focusing particularly on cold waves during winter); such claims are not based in our current understanding of the science but instead misrepresent elements of the climate system when placing the importance of ‘narrative’ above the state of our knowledge on physical linkages and how they drive extreme weather events.

Background Reading

Richard Hall (University of Bristol)
Giorgia di Capua (Potsdam Institute for Climate Impact Research (PIK))


Conferences and Workshops
  • EGU General Assembly 2019 (April 2019). Talk: Using Bayesian Networks to investigate the influence of ongoing Arctic climate change on midlatitude circulation and extreme weather.:
Training courses
  • Gotham International Summer School, hosted by Potsdam Institute for Climate Impact Research (PIK). September 2021

Social Links
University Departmental Website:
Personal Website:




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