New Study Predicts Higher Sea-Level Rise than IPCC Projections

According to the predictions of a new international study headed by the Nanyang Technological University (NTU), Singapore, the faster melting of polar ice sheets than projected earlier may lead to a nearly 1.3 m rise in the ocean levels by 2100.

Icebergs in Ilulissat Icefjord, Greenland. The melting of the ice sheets in Greenland and Antarctica can have a devastating impact on the world. Image Credit: Copyright—Mark Garten/UN Photo.

The new study was published recently in Climate and Atmospheric Science and predicts sea-level rise considerably higher than those projected by the UN’s International Panel on Climate Change (IPCC) in its 2014 Fifth Assessment Report, and also in a special report on oceans and the cryosphere published in September 2019.

The researchers used a survey of opinions offered by 106 experts to estimate global mean sea-level variations under low- and high-emission conditions. Answers to open-ended questions in the survey imply that elevations in upper-end estimates emerged from the latest influential studies on the effect of the instability of marine ice-cliff on meltwater contribution to global mean sea-level rise.

According to Benjamin Horton, acting chair of NTU’s Asian School of the Environment and lead author of the study, under a high-emission condition, with a warming of 4.5 °C, the study predicts an increase of up to 1.3 m by 2100 and up to 5.6 m by 2300.

About one-third of current rise comes from thermal expansion as water grows in volume as it warms, while the rest comes from the melting of ice on land. If all the ice in Greenland melted, it would raise sea levels by seven metres, [while] you only need to melt a small part of the Antarctic ice sheet to cause devastating impacts.

Benjamin Horton, Acting Chair, Asian School of the Environment, Nanyang Technological University

Horton stated that the biggest worry is the melting of giant ice sheets in Greenland and Antarctica. He noted that Antarctica, approximately the size of the United States and covered in ice up to 2 km in thickness, has adequate water to increase the sea levels by 65 m.

Horton added that satellite-based measurements of Antarctica and Greenland reveal the melting of ice sheets at an alarming rate. “For example, Greenland's glaciers went from dumping only about 51 billion tonnes of ice into the ocean between 1980 and 1990, to losing 286 billion tonnes between 2010 and 2018,” he noted.

According to Horton, predicting sea level rise and understanding their uncertainties are crucial to making informed decisions in relation to mitigation and adaptation.

Horton emphasizes that rising seas increase the susceptibility of cities and the related infrastructure lining several coastlines across the globe due to coastal erosion, flooding, salinization of ground and surface waters, and degradation of coastal habitats.

As an example of the impact of a high-emission scenario, once the ocean rises by 1.3 meters, it will affect 16 per cent of Bangladesh's land area and 15 per cent of its population. That affects 22,000 square kilometres and 17 million people.

Benjamin Horton, Acting Chair, Asian School of the Environment, Nanyang Technological University

According to Andrea Dutton, a professor in the geoscience department of the University of Wisconsin, Madison, the research is vital as it depends on the best estimates of sea level rise by several experts.

Conducting multiple, or repeat, expert elicitations also enables this response to be tracked over time to determine how these estimates may have changed over time as research evolves.

Andrea Dutton, Professor, Department of Geoscience, University of Wisconsin–Madison

The study demonstrates that densely populated coastlines of the Asia-Pacific region will be affected by future sea-level rise even carbon emissions are reduced to zero today, added Dutton. “The results of this study, however, emphasise that there is the potential to reduce the ultimate magnitude of that sea-level rise by reducing our emissions.”

Journal Reference:

Horton, B. P., et al. (2020) Estimating global mean sea-level rise and its uncertainties by 2100 and 2300 from an expert survey. npj Climate and Atmospheric Science.


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