Comment & Analysis
What is AMOC and why is it slowing down?
Ocean current systems play a key role in determining global climate through the redistribution of heat as well as other environmental quantities. Some of these systems are on a large spatial scale, for example the basin-scale Atlantic Meridional Overturning Circulation (AMOC) which has a significant influence on the climate of north-east America, north-west Europe, Scandinavia, and the African continent. In this regard, AMOC is the dominant mechanism of heat transport in the Atlantic, through northward-flowing warm near-surface currents and cold southward-flowing deep-sea currents, and projections from climate models consistently predict a weakening of the circulation as global temperature rises in response to continued greenhouse gas emissions. The anticipated slowdown is primarily driven by changes to the density of the sea water (which is dependent on salinity and temperature) at the northern end of the circulation due to the introduction of fresh water from melting ice sheets in Greenland.
How will the slowdown impact engineered systems?
A decline in the strength of the AMOC will have significant and far-ranging implications for the global climate, including widespread cooling in the North Atlantic region; altered atmospheric circulation; large-scale changes to precipitation patterns; a postponement of an ice-free Arctic; and increased temperature extremes in sub-Saharan Africa [1] . Such changes will impact the built environment, physical infrastructure and other engineered systems, potentially subjecting them to environmental conditions for which they have not been designed or adapted to cope.
For example, in the Northern Hemisphere, widespread decreases in surface air temperatures are anticipated, including cooling by several degrees in the UK, likely delaying the full extent of global warming (a complete collapse of the AMOC could potentially lead to a 5°C reduction in the UK average temperature compared with that which would otherwise occur). Changes to atmospheric circulation will potentially displace the mid-latitude jet stream poleward in winter leading to an eastward extension of a strengthened storm track over northern Europe. The latter may increase the frequency and intensity of winter storms tracking over the UK and the continent; result in higher seasonal precipitation and mean wind speeds; and increase snowfall rates, snow depths and snow cover duration. In summer, a weakened AMOC would decrease precipitation in northern Europe due to reduced evaporation. However, local increases in summer precipitation are expected in parts of southern Europe and there is also an increased probability of heatwaves over the continent. In the UK, heatwaves and drier conditions, with summer rainfall up to 40% less, could increase drought impacts.
What are the implications for adaptation and the engineering profession?
The engineering profession, in collaboration and cooperation with many other allied professions, is increasingly working on our response to climate change through adaptation and resilience building activities. The latter includes updating design methods, codes and regulations, both for new builds/manufactures and retrofits; modifying operational processes, monitoring and control systems, and maintenance regimes; and developing new technologies and approaches. Such initiatives are also being supported through the production of reports, adaptation guidance, policy reviews, and changes to education and training curricula. However, this current work does not consider the climate change related impacts of an AMOC slowdown and the associated uncertainties, hazards, vulnerabilities and risks for the built environment, physical infrastructure and other engineered systems.
To begin a discussion regarding these challenges and to stimulate the profession to start taking action, the Institution is convening two events in the near future. The first of these is a 1 hour, free to attend, webinar at 12 midday (BST) on Tuesday 20 May, see Adapting engineered systems to climate impacts from changing Atlantic ocean currents. for details and registration. The second is a 2-hour interactive in-person workshop session from 13:00 – 15:00 on Thursday 3 July in association with the Global Tipping Points conference being held at Exeter University. More details on the latter can be found by clicking on the 3 July dropdown here: Programme - Global Tipping Points. The workshop is free to attend (delegates are invited to join the conference lunch between 12:00 and 13:00 free of charge if they so wish). If you would like to attend, please register here.
[1] It is important to note that the detailed patterns and exact magnitude of potential impacts depend on the extent of AMOC decline and also vary with different climate models and emission scenarios.
[2] For details of the reference sources for this article please contact the author as directed above.