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New paper ‘The causes of sea-level rise since 1900’ ( https://www.nature.com/articles/s41586-020-2591-3#article-info) just came out! We have shown that we can close the ‘sea-level budget’ since 1900. That means, that we can now explain the causes of the observed #sealevel changes since 1900. (1/n)
That used to be an unsolved problem: global sea-level reconstructions showed more sea-level rise than could be explained by what was known about ice melt and thermal expansion of sea water due to the warming oceans. Now, we finally show that everything sums up well. (2/n)
In the figure you can see that global sea level has risen by about 20 cm since 1900, which has been caused by thermal expansion and ice melt, while there;’s now more liquid water stored on land than in 1900. (3/n)
This decrease is because we have impounded a lot of water in dammed reservoirs, such as the lakes behind Hoover Dam and the Three Gorges Dam in China. At the height of the dam construction era, all the new dams almost brought sea-level rise to a halt! (4/n)
Over the 20th century, most sea-level rise is caused by glacier melt, while the recently increased mass loss Greenland and Antarctica are catching up quickly. Sea level is also rising at an accelerated rate because of thermal expansion (5/n)
How did we come to these results? At first, we have access to more sea-level observations: due to extensive data rescue efforts, led by @NOCnews Peter Hogarth, we have more records of long-term sea-level rise ( http://doi.wiley.com/10.1002/2014JC009976). (6/n)
We also use a very large database of GPS measurements from the University of Nevada, Reno ( http://geodesy.unr.edu ) to check for vertical motions of these tide-gauge instruments. (7/n)
We found that some previous sea-level reconstructions slightly overestimated sea-level rise before the 1950s, while the ongoing high rates are a robust finding and is a truly global phenomenon. We find similar sea-level changes as Hay et al. ( http://www.nature.com/articles/nature14093) (8/n)
We use the new reconstruction of how much glaciers have melted and disappeared, based on the work of David Parkes and Ben Marzeion ( http://www.nature.com/articles/s41586-018-0687-9), which shows that glaciers have led to about 8 cm of sea-level rise since 1900. (9/n)
Another novelty is the use of an observation-based estimate of global thermal expansion from @laurezanna , ( http://www.pnas.org/lookup/doi/10.1073/pnas.1808838115) who found that the heat absorbed by the oceans has led to about 6 cm of sea-level rise since 1900. (10/n)
This 'budget closure' is good news for our trust in sea-level projections, which are often computed by summing up estimates of the individual components. With this study we show that we're not missing components that contribute to century-scale sea-level changes. (11/n)
This work is a team effort with many collaborators: Felix Landerer, @AlpineGlaciers, Lambert Caron @NASAClimate @NASAJPL, David Parkes, @vwhumphrey, @DangendorfSonke, Peter Hogarth, @laurezanna, @Lijing_Cheng , and Henry Wu (12/n)
Also a big shout-out to all the people who have collected all the GPS data, hydrographic surveys, tide-gauge instruments, fieldwork on the ice sheets and much more whose work has led to reliable long-term climate observations! (13/n)
Codes and data are also publicly available:
https://github.com/thomasfrederikse/sealevelbudget_20c
https://podaac.jpl.nasa.gov/dataset/JPL_RECON_GMSL
https://zenodo.org/record/3862995
Enjoy the read!
(14/n)
https://github.com/thomasfrederikse/sealevelbudget_20c
https://podaac.jpl.nasa.gov/dataset/JPL_RECON_GMSL
https://zenodo.org/record/3862995
Enjoy the read!
(14/n)
No institutional access to the paper? Click here: https://rdcu.be/b6mlB
