October 2018 issue

Last update: 13/11/2018

After a break of eight month since the last sea level review I finally have some time to continue. My eight months old son started to let us sleep at night so I have some more time on my hands. Here are the three highlights of October.

The first one is an update of the Kopp et al. 2015 paper. One of the main conclusions of that paper was that “The 20th century rise was extremely likely (P>=95%) faster than during any of the 27 previous centuries”. It has now been updated in Kemp et al. 2018 by: “The global component confirms that 20th century sea-level rise occurred at the fastest, century-scale rate in over 3000 years (P > 0.999)” so there is now little doubt about that. This shows that global warming already had a detectable effect on the acceleration of sea level rise. In fact, the acceleration itself seems to be increasing fast. It is estimated by Dangendorf et al. 2017 at around 0.02 mm.yr-2 for the period 1902-1990 while the estimate during the satellite altimetry period (1993-now) is around 0.10 mm.yr-2 (section 3.1.2 in WCRP, 2018). This is a large difference that I haven’t seen discussed in the literature yet but it makes you think twice about the interpretation of sea level projections that assume a constant acceleration in the 21st century e.g. Nerem et al. 2018.

The second highlight is from Greenland surface mass balance research. In two papers by Hanna et al. 2018 and Delhasse et al. 2018 a research group from the Universiy of Liège and other international colleagues suggest that: (1) CMIP5 climate models do not reproduce recent observed circulation change in Greenland and (2) if these changes persist in the 21st century they expect a contribution from Greenland surface melt to sea level two times bigger than what was projected in the IPCC AR5 report. So that would be 10 cm instead of 5 for RCP4.5 or 20 cm instead of 10 for RCP8.5. There is no consensus yet about that issue but it will be something to keep an eye on when the CMIP6 model data become available. More about these papers here.

There cannot be a monthly review without talking about Antarctica so the third highlight is about the Antarctic ice sheet. This month the Pine Island glacier, a fast flowing glacier in West Antarctica that recently accelerated, shed a new iceberg (see picture bellow). Calving events are a natural way for the ice sheet to evacuate the surface snow fall but for the Pine Island glacier there is now a clear imbalance between mass gain through snow fall and mass loss through calving/basal melt. The calving front is now retreating inland as shown in this beautiful animation from Stef Lhermitte.

Bibliography:

Dangendorf, S., Marcos, M., Wöppelmann, G., Conrad, C. P., Frederikse, T., & Riva, R. (2017). Reassessment of 20th century global mean sea level rise. Proceedings of the National Academy of Sciences, 114(23), 5946–5951. http://doi.org/10.1073/pnas.1616007114

Delhasse, A., Fettweis, X., Kittel, C., Amory, C., & Agosta, C. (2018). Brief communication: Impact of the recent atmospheric circulation change in summer on the future surface mass balance of the Greenland ice sheet. The Cryosphere Discussions, 12(April), 1–13. http://doi.org/10.5194/tc-2018-65

Hanna, E., Fettweis, X., & Hall, R. J. (2018). Brief communication: Recent changes in summer Greenland blocking captured by none of the CMIP5 models. The Cryosphere, 12(10), 3287–3292. http://doi.org/10.5194/tc-12-3287-2018

Kemp, A. C., Wright, A. J., Edwards, R. J., Barnett, R. L., Brain, M. J., Kopp, R. E., … van de Plassche, O. (2018). Relative sea-level change in Newfoundland, Canada during the past ~3000 years. Quaternary Science Reviews, 201, 89–110. http://doi.org/10.1016/j.quascirev.2018.10.012

Kopp, R. E., Kemp, A. C., Bittermann, K., Horton, B. P., Donnelly, J. P., Gehrels, W. R., … Rahmstorf, S. (2016). Temperature-driven global sea-level variability in the Common Era. Proceedings of the National Academy of Sciences, 113(11), E1434–E1441. http://doi.org/10.1073/pnas.1517056113

Nerem, R. S., Beckley, B. D., Fasullo, J. T., Hamlington, B. D., Masters, D., & Mitchum, G. T. (2018). Climate-change–driven accelerated sea-level rise detected in the altimeter era. Proceedings of the National Academy of Sciences, 0, 201717312. http://doi.org/10.1073/pnas.1717312115

WCRP. (2018). Global sea-level budget 1993–present. Earth System Science Data, 10(3), 1551–1590. http://doi.org/10.5194/essd-10-1551-2018