Observing the winds over Greenland is key to improving global sea level rise forecasts
A new study conducted by an international team of American, English and Belgian scientists using the MAR, the Regional Atmospheric Model, developed at ULiège by Xavier Fettweis, director of the Climatology Laboratory (SPHERES / Faculty of Science), demonstrates the essential role played by high-latitude winds in accelerating the melting of the ice in Greenland. This study is the subject of an article published in Nature Communications.
T
he Greenland ice sheet has been losing ice mass at an accelerated rate in recent decades, leading to a rise in global sea levels. A trend that is unfortunately expected to continue with the current human-induced climate change. An international group of scientists, using a unique modelling approach, have been able to show that between 1990 and 2012, observed wind changes can explain more than half of the sea level rise from Greenland mass loss. However, global climate models, which underestimate the observed increase in melting, suggest that the melting is mainly due to a generally warmer atmosphere resulting from increased greenhouse gas concentrations due to human activities and not associated with regional wind changes. This bias can seriously limit the ability of models to make accurate predictions of future sea level rise, given that if such circulation changes are repeated in the future, the MAR model suggests that future projections of sea level rise from Greenland ice sheet melt will need to be increased at least twofold (van de Wall et al., 2022).
The authors analysed modern satellite observations and climate datasets - including the MAR model developed at ULiège - as well as historical climate data from ice cores and tree rings, which have consistently shown that large-scale atmospheric circulation and winds have played a key role in the warming of Greenland and its surroundings over at least the last 400 years. Scientists suggest that these winds are linked to the decadal variability of surface temperatures in the tropical Pacific Ocean. However, many uncertainties remain, including the links between the tropics and the Arctic, and it is unclear whether global climate models respond correctly to changes in tropical sea surface temperatures in the same way as observations. The authors warn that although the climate models used in the latest IPCC report project Greenland's melting to be more consistent with observations than the previous generation of these models, these projections should be treated with caution without properly constraining the atmospheric circulation in these models. This new study demonstrates, once again, that there is an urgent need to improve the understanding of the climate changes observed on the Greenland ice sheet but also in Europe, where the models also underestimate the changes in atmospheric circulation observed in summer. These same changes explain why the climate anomalies currently observed in Belgium in recent summers are 'ahead' of what the models project for our decade. This would allow for more effective adaptation and mitigation plans to be developed to address the challenging threat of global sea level rise, which could reach 1.6m by 2100 in the worst case (van de Wall et al., 2022).
Lead author of the study, Daniel Topal (Centre for Astronomy and Earth Science Research, University of California Santa Barbara), said: "A key research priority should be to determine why models tend to overestimate the magnitude of warming induced by anthropogenic forcing in parts of the Arctic without suggesting a change in the general atmospheric circulation, as has been observed and modelled by the MAR model since 2000. It is essential that we can determine precisely how warming impacts the interactions between the atmosphere, ice and ocean in the Arctic but also in Europe," adds Xavier Fettweis, "knowing that we are also observing changes in atmospheric circulation that are driving the warming of our summers but that are underestimated by global climate models. Xavier Fettweis concludes that a more detailed knowledge of the driving factors will allow us to better prepare for future scenarios of melting of the Greenland ice sheet, which could be much greater than predicted in the IPCC report if these circulation changes continue in the coming decades.
Scientific reference
- Dániel Topál, Qinghua Ding, Thomas J. Ballinger, Edward Hanna, Xavier Fettweis, Zhe Li & Ildikó Pieczka, Discrepancies between observations and climate models of large-scale wind-driven Greenland melt influence sea-level rise projections, Nature Communications, 14 November 2022. doi : 10.1038/s41467-022-34414-2
- van de Wal, R. S. W., Nicholls, R. J., Behar, D., McInnes, K., Stammer, D., Lowe, J. A., Church, J. A., DeConto, R., Fettweis, X., Goelzer, H., Haasnoot, M., Haigh, I. D., Hinkel, J., Horton, B. P., James, T. S., Jenkins, A., LeCozannet, G., Levermann, A., Lipscomb, W. H., & White, K. (November 2022). A High‐End Estimate of Sea Level Rise for Practitioners. Earth's Future, 10 (11). doi:10.1029/2022ef002751
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