I’ve explained several times in the course of media comments that, when it comes to the sea level rise that you experience, it really matters where the water comes from. This point still seems to cause confusion so I’ve written a super fast post on it.
Waves from the Storm Surge that hit Denmark in October 2023 credit: Sebastian Pelt
We very often talk about a metre or two of sea level rise by the end of the century, but in general that refers to global average sea level. And much like a global mean temperature rise doesn’t tell you very much about the kind of temperature changes you will experience in your location due to weather or climate, global mean sea level is also not very informative when talking about preparing your local community for sea level rise. There are other local factors that are important, (see below), but here I’m going to mostly focus on gravity.
Imagine that sea level is more or less stable around the earth (which it was, more or less, before the start of the twentieth century). Just like the moon causes tides because its gravity exerts a pull on the oceans, the ice sheets are large masses and their gravity also attracts ocean water, so the average sea level is higher closer to Greenland and to Antarctica. But there is only a finite volume of water in the oceans, so a higher sea level close to the ice sheets means lower sea levels further away in the tropics for example.
As the ice sheet melts and gets smaller, its gravitational pull becomes smaller so the average height of the sea around Greenland and Antarctica is lower than it was before, but the water gets redistributed around the earth until it is in equilibrium with the gravitational pull of the ice sheets again. The sea level in other places is therefore much higher than it would have been without that gravitational effect.
And in general, the further away from an ice mass you are, the more these gravitational processes affect your local sea level change. In Northern Europe, it often surprises people (also here in Denmark) to learn that while Greenland has a small influence on our local sea level, it’s not very much because we live relatively close to it, however the loss of ice from Antarctica is much more important in affecting our local sea level rise.
Currently, most of the ice contributing to sea level is from the small glaciers around the world, and here too there is an effect. The melt of Alaska and the Andes are more important to our sea level than the Alps or Norwegian glaciers because we are far from the American glaciers but close to the European ones.
This figure below illustrates the processes:
Processes important for local sea level include changes in land height as ice melts but also the redistribution of water as the gravitational attraction of the ice sheets is reduced. The schematic representation is from the Arctic assessment SWIPA report Figure 9.1 from SWIPA 2017
This is partly why the EU funded PROTECT project on cryosphere contributions to sea level rise, which I am currently working on, has an emphasis on the science to policymakers pipeline. We describe the whole project in this Frontiers paper, which includes a graphic explaining what affects your local sea level.
As you can see, it very much depends on what time and spatial scale you’re looking at, with the two ice sheets affecting sea level on the longest time scales.
Figure 1 from Durand et al., 2021 Illustration of the processes that contribute to sea level change with respect to their temporal and spatial scales. These cover local and short term effects like storm surges, waves and tides to global and long-term changes due to the melting of ice sheets.
In the course of the project some of the partners have produced this excellent policy briefing, which should really be compulsory for anyone interested in coastal developments over the next decades to centuries. The most important points are worth highlighting here:
We expect that 2m of global mean sea level rise is more or less baked in, it will be very difficult to avoid this, even with dramatic reductions in greenhouse gas emissions. But the timescale, as in when that figure will be reached, could be anything from the next hundred years to the next thousand.
Figure from PROTECT policy briefing showing how the time when average global sea level reaches 2m is strongly dependend on emissions pathway – but also that different parts of the world will reach 2m of sea level rise at very different times, with the tropics and low latitudes in general getting there first.
What the map shows is that the timing at which any individual place on earth reaches 2 m is strongly dependent on where on earth it is. In general lower latitudes close to the equator will get to 2m before higher latitudes, and while there are ocean circulation and other processes that are important here – to a large extent your local sea level is controlled by how close to the ice sheets you are and how quickly those ice sheets will lose their ice.
There are other processes that are important – especially locally, including how much the land you are on is rising or sinking, as well as changes in ocean and atmosphere circulation. I may write about these a bit more later.
Feel free to comment or ask questions in the comments below or you can catch me on mastodon:
Hands-up who is looking for a new and very cool job in ice sheet and climate modelling and developing new machine learning tools?
REMINDER: 4 days left to apply for this PhD position with me at DMI looking at Antarctic Ice Sheet mass budget processes and developing new Machine Learning models and processes.
UPDATE 2: The PhD position on Antarctica is now live here. Deadline for Applications 18th February!
UPDATE: It’s not technically a PRECISE job, but if you’re a student in Copenhagen and are looking for a part-time study job (Note that this is a specific limited hours job-type for students in higher education in Dnmark) , DMI have got 2 positions open right now, at least one of which will be dedicated to very related work – namely working out how well climate and ice sheet models work when compared with satellite data. It’s part of a European Space Agency funded project that I and my ace colleague Shuting Yang, PI on the new TipESM project, are running. Apply. Apply. Apply…
This is a quick post to announce that our recruitment drive is now open. We’re split across three institutes. We are two in Copenhagen, ourselves at DMI and the Niels Bohr Institute at the University of Copenhagen, and then the University of Northumbria in Newcastle, UK.
The PI at the Niels Bohr Institute is the supremely talented Professor Christine Hvidberg, aided by material scientist and head of the institute, Joachim Mathiesen. I am leading for DMI, and the Northumbria work is led by Professor Hilmar Gudmundsson. We are also very fortunate to have the talents of Aslak Grindsted, Helle Schmidt, Nicolas Rathmann and Nicolaj Hansen already on board.
The project is already very cohesive between institutes, we’ve been working together for some time already and know each other well.
We have a good budget for travel and exchanges between groups, workshops, symposia, summer schools and the like, but perhaps more importantly, all the positions are focused at the very cutting edge (apologies for the cliche) of climate and ice sheet modelling. We are developing not just existing models and new ways to parameterise physical processes, but we also want to focus on machine learning to incorporate new processes, speed-up the production of projections for sea level rise, not forgetting an active interface with the primary stakeholders who will need to use the outcomes of the project to prepare society for the coming changes.
There’s also a healthy fieldwork component (particularly in Greenland, I don’t rule out Antarctica either), and if you’re that way inclined, some ice core isotope work too. So, if you’re looking for a new direction, feel free to give me a shout. I’m happy to talk further.
Links to all the openings, will be updated as they come out, these are currently open and have deadlines at the end of January:
The International Cryosphere Climate Initiative has put together a new petition for scientists to sign. I’m a little sceptical that this kind of “clicktivism” makes much difference, but there are many many lobbyists from polluting industries at the COP28 and rather fewer scientists. And how else to draw attention to what is one of the most visible and urgent effects of climate change?
The petition is aimed at:
” all cryosphere scientists globally; as well as those working on emissions pathways: and those in the social sciences with research on adaptation, loss and damage and health impacts. This includes research and field associates, as well as doctoral students — because you are the future, and will be dealing with the impacts of climate change in the global cryosphere throughout your lives, as well as your professional careers.”
ICCI
The list of signatories so far already includes many rather senior scientists, so take this as a challenge to add your signature if you work in the cryosphere/climate space. It takes only a minute to sign and there are many familiar names on the list.
I’m not sure how else to emphasise the urgency of real action at COP 28.
As a coincidence though, and as I posted on mastodon the image below appears in Momentum, a plug-in on my web browser with a new photo every day. Today’s is this beautiful image of the Marmolada glacier in Italy by Vicentiu Solomon.
It’s a gorgeous but very sad picture – this is one of the faster disappearing #glaciers in the world and to hear more about the consequences of cryosphere loss, take a look at the policy brief produced by the PROTECT project on the sea level rise contributions from glaciers and ice sheets. It also contains this eye opening graphic:
A 2 metre rise in sea level is almost inevitable. The uncertainty is on the timing which is somewhere between one century and the next 2 thousand years, depending on where you are in the world, but, more importantly given COP28, how fast fossil fuels are phased out. You can download the whole thing here.
Sterna Paradisaea 