Sea level rise is caused by the melting of glaciers and continental ice sheets and is one of the most severe impacts of human caused climate change. However, as this is an interaction of many different factors, a reliable forecast is associated with major challenges. In a study published in the renowned journal Nature, 80 international researchers have now computed updated projections of future sea level rise, based on an unprecedented combination of computer models and statistical techniques. The projections were realized for the latest socio-economic scenarios to inform the Intergovernmental Panel on Climate Change's Sixth Assessment report, which will be published later this year. "It is the unprecedented combination of sophisticated climate and glacier models from 38 international groups which makes this study so important to better quantify by how much sea level will rise in the future," highlights Dr. Fabien Maussion from the Department of Atmospheric and Cryospheric Sciences at the University of Innsbruck. The glaciologist contributed to the study by computing projections of mountain glacier changes with the OGGM glacier evolution model developed at the University of Innsbruck. The key result: The research predicts that if we limit global warming to 1.5°C, Greenland ice sheet losses would reduce by 70%, and glacier losses by half, compared with current emissions pledges. For Antarctica, the predictions are the same for different emissions scenarios, because it is currently unclear whether snow falling in the cold interior of the ice sheet will offset melting at the coasts. However, under a 'pessimistic' storyline, with much more melting than snowfall, Antarctic ice losses could be five times larger.
1.5°C target can limit the damage
"Ahead of COP26 this November, many nations are updating their pledges to reduce greenhouse gas emissions under the Paris Agreement. Global sea level will continue to rise, even if we halt all emissions now, but our research suggests we could limit the damage," explains Dr Tamsin Edwards, Reader in Climate Change at King’s College London and lead author of this study. If pledges were far more ambitious, central predictions for sea level rise from melting ice would be reduced from 25 cm to 13 cm in 2100, with a 95% chance of being less than 28 cm rather than the current upper end of 40 cm, the researchers agree. The probability of at least being below 28 centimetres would even be 95 percent - instead of the current upper limit of the uncertainty range of 40 centimetres. " This would mean a less severe increase in coastal flooding," says Edwards. Glaciers and ice sheets are currently responsible for around half of global sea level rise, with most of the rest arising from expansion of the oceans as they warm. Previous predictions had used older emissions scenarios, and could not explore uncertainty about the future as thoroughly due to the limited number of simulations. This statistically-based study updates the scenarios, and combines all sources of land ice into a more complete picture that predicts the likelihood of different levels of sea level rise. "Despite large uncertainties about the fate of the Antarctic Ice Sheet, this study conveys a clear and unequivocal message about the importance of limiting warming to 1.5°C to protect coastal regions. But sea-level rise is not the only consequence of glacier retreat, which will also impact freshwater resource in many glaciated basins as well as increase the risks of glacier related hazards such as landslides and floods. Here also, we can show that every tenth of degree matters and makes a difference for future generations," stresses Fabien Maussion.