It means that sea levels could have risen by another 17 centimeters by the end of the century.

At the moment, the ice in Greenland and Antarctica is melting at breakneck speed. “The ice in both regions is now melting six times faster than in the 1990s,” researcher Tom Slater told Scientias.nl . “That’s an alarming increase.” Using simulations and climate models, scientists are trying to map out the exact consequences of this for sea level. And now, satellite observations are revealing that the melt in Greenland and Antarctica is going so fast that both regions are conforming to the worst climate scenario imaginable.

Worst case climate scenario
At the beginning of the 1990s, scientists began to systematically monitor the ice sheets in Greenland and Antarctica. And it has been going fast ever since. Between 1992 and 2017, Greenland and Antarctica together lost about 6.4 trillion tons of ice and raised sea levels by about 17.8 millimeters. And if this continues, we will be heading for the melt and associated sea level rise that the Intergovernmental Panel on Climate Change (IPCC) outlined in its fifth climate report as the worst possible scenario (see box). It means that the ice sheets are expected to raise sea levels by another 17 centimeters.

Contribution to sea level rise of Greenland and Antarctica. 
Image: IMBIE

The fact that we are now on track for the predicted ‘worst case climate scenario’ is quite alarming. “It’s very concerning,” says Slater. “Because the ice sheets are now following this worst conceivable scenario, we now have to come up with a new scenario. Underestimating the degree of sea level rise can have serious consequences. It may mean, for example, that our coastal defenses are not good enough, or that we may not have built new infrastructure in time. ”

The International Panel on Climate Change (IPCC for short) regularly issues climate reports in which it sketches the future of our climate and our planet. The last (and fifth) climate report was published in 2014 and contains several climate scenarios. Some of these scenarios are very optimistic and assume that we will embrace a very ambitious climate policy worldwide and thus manage to reduce CO2 emissions in the short term and the increase in CO2 concentration in the atmosphere and thus global warming. know to limit. Other scenarios are more gloomy and assume a situation in which little or no action is taken to reduce emissions and where the earth continues to warm, with all the associated consequences.

If the sea level has indeed risen by another 17 centimeters by the end of the century, there are quite a few consequences. “A rise in sea levels increases the risk of flooding, exacerbates hurricane damage, erodes coastal areas and threatens the land on which people live,” notes Slater. “A sea level rise of another 17 centimeters is enough to double the frequency of storm surge flooding in Europe. It means millions more people will be affected by annual coastal flooding. ”

Alarmingly fast
The findings from the study indicate that the ice in Greenland and Antarctica has withered away very quickly. “At the time, when the IPCC’s first climate report was published in 1990, the ice sheets were seen as a more passive element of the climate system,” says Slater. “It would take at least hundreds of years for them to respond to climate change. But in just three decades, our understanding of the ice sheets has completely changed. We have now seen how quickly they respond to climate change. ”

Causes of the melt

There are several reasons why the ice in Antarctica and Greenland is currently melting so hard. For example, the melt in Antarctica can mainly be traced back to the warming of the surrounding ocean. This affects the glaciers that flow into the sea from below, making the parts of the glaciers resting on the water thinner. Because the mass of these glacier tongues decreases, they are also less able to counterbalance the land-based part of the glacier. The result is that it starts to flow faster and dump ice into the sea at an accelerated rate. This same process is also happening in Greenland and it is estimated to be responsible for about half of the melt seen here. The other half is due to rising surface temperatures that affect the ice from above.

The fact that we now have a better picture of this is entirely due to satellite observations, according to Slater. Scientists are using a variety of missions, including ESA’s ERS-1, ERS-2, Envisat and CryoSat, in addition to the EU’s Copernicus Sentinel-1 mission – to track changes in the volume, flow and mass of ice sheets. “Satellites are our only way to regularly monitor the vast and remote areas,” says Slater. “These are essential for providing measurements that we can use to validate ice sheet models. They not only tell us how much ice is being lost, but they also help us identify and understand which parts of Antarctica and Greenland are losing ice and through what processes. Both are critical to improving ice sheet models. ”

Action
Despite the gloomy picture of the future, Slater emphasizes that it is not too late. “There is still time for us to take action,” he says. “We still have the ability to curb emissions so that the Earth does not warm beyond 1.5 degrees Celsius as set in the Paris Climate Agreement. That way we can reduce the risks of the most catastrophic consequences of climate change. We must also continue to plan and build suitable coastal defenses as we are now facing more sea level rise than expected. ”

Immense dam
Dutch scientists are also working on this idea. At the beginning of this year, an oceanographer from the Royal Netherlands Institute for Sea Research, for example, investigated whether an endless dam could protect us from the consequences of the expected future sea level rise.. The idea is to build a dam of about 475 kilometers between the north of Scotland and the west of Norway. In addition, a 160 km long dam will be built between the western tip of France and the southwest of England. This dam protects more than 25 million people from ever-rising sea levels. This is of course a rigorous decision with enormous consequences and the question is whether we should want to. But we may not have the choice at all and the construction of such a dam is our only option. “The most suitable coastal defense varies from location to location,” says Slater. “In addition, this depends on local geographic and human factors.

All in all, the findings from the study give us an accurate picture of the changes currently occurring in Greenland and Antarctica. And that picture is not very rosy. The researchers plan to keep a close eye on the polar regions with the help of future satellite missions. Consider, for example, the following major Copernicus candidate missions CRISTAL, ROSE-L and CIMR. And then we will learn even better what our future will look like.

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