Effects of global warming visible for tens of thousands of years

Effects of global warming visible for tens of thousands of years

Denmark, Netherlands, Flanders, parts of Germany and UK under water according to VUB study on sea level rise

Most projections of global sea level rise run until the end of this century. However, the melting of the ice sheets is a very slow process and once the ice sheets are out of balance, it may take hundreds to thousands of years before a new equilibrium is found. In his doctoral study, published in the journal Earth System Dynamics, glaciologist Jonas Van Breedam has made projections for sea level rise over the next 10,000 years. He used linked models of the Greenland and Antarctic ice sheets, the atmosphere and the ocean: “Emissions of greenhouse gases over the next 30 to 200 years could result in a global average sea level rise of 9 to 37 metres over the next 100 centuries. Flanders, the Netherlands, Denmark, parts of Germany, parts of the UK would be almost completely below sea level.”

The VUB Research Group in Physical Geography, led by Prof Philippe Huybrechts, lead author of the IPCC, made projections for sea level rise over the next 10,000 years. They did this for a series of climate scenarios ranging from a CO2 peak over the next 30 years to the emission of most of the available CO2 reserves over the next 200 years. The highest scenario also takes into account an increased greenhouse effect when the permafrost on land and ocean floor melts and releases methane in large quantities.

Depending on these greenhouse gas emissions, sea levels will rise by between 9.2m and 37.4m. The Greenland ice sheet will disappear completely in each scenario, while the Antarctic ice sheet will remain largely intact in a low-emission scenario and could lose up to half of its mass in a high-emission scenario. It is only after 10,000 years that sea level will be in balance with climate change and the rise will fall back to a maximum of 5cm per 100 years. In the high-emission scenario, sea levels will rise by more than 1m per century on average during the first 2,000 years. For the low-emission scenario, the rate of sea-level rise is 10 times lower for the same period, at an average of 11cm per century. The rate of sea-level rise is thus highly dependent on the total amount of CO2 emitted.

In a high-emission scenario, low lands of western Europe under water.

The current rise in sea level is due to the expansion of ocean water, which is becoming warmer, and due to the melting water of mountain glaciers. Mountain glaciers are likely to lose most of their volume by the end of the 21st century. However, the biggest contribution will come from the polar ice sheets. The Greenland ice sheet will contribute most to sea level rise in a low-emission scenario, while the Antarctic ice sheet will contribute most in a high-emission scenario.

This is due to the gravitational pull of the ice sheets on the ocean waters surrounding them. As these ice sheets melt, the sea level near the ice sheets rises relatively less or even falls because the gravitational pull between the ice sheet and the surrounding water disappears. But further away from the ice caps, sea levels rise faster than the average. Because the Antarctic ice sheet is far away from Belgium, the sea level rise due to the melting of land ice in Antarctica would have more effect than the melting of land ice in Greenland.

Jonas Van Breedam: “This study shows that the effect of current warming on sea level will remain visible for thousands of years, mainly due to the slow response of the Greenland and Antarctic ice sheets to a change in temperature. If we cannot quickly reduce CO2 emissions to zero, Flanders, with the exception of part of Limburg, will be almost completely below sea level.”

Note for the press: Maps of specific regions, showing e.g. the rise in sea level in Belgium over time, are available on request.

Contact:

Jonas Van Breedam - jonas.van.breedam@vub.be – +32 494 60 25 14

Philippe Huybrechts - philippe.huybrechts@vub.be – +32 474 99 33 95

Figure 1: Increase in global sea level over the next 10,000 years.

Figure 2: Contribution of the Antarctic ice sheet, the Greenland ice sheet, the expansion of ocean water and mountain glaciers to the global sea level for a low-emission scenario (MMCP2.6) and a high-emission scenario (MMCP-feedback).

Publication in Earth System Dynamics: https://doi.org/10.5194/esd-11-953-2020

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