The Greenland ice sheet covers almost all of Greenland and is the second largest ice cap in the world with an area of around 1.7 million square kilometers. Only Antarctica is bigger.
If all the ice on Greenland were to melt, all the world's oceans would rise by seven meters. Fortunately, we do not have to worry about that horror scenario.
But the ice does melt, and it will contribute to higher sea levels, but not on such a scale. A 30 centimeter log ruler will probably be enough to measure any contributions from the Greenland ice until the year 2100.
Stefan Hofer at the Department of Geosciences at the University of Oslo, together with other researchers, has tried to quantify exactly how much by using the very latest climate models.
“We found that these new models are more sensitive to greenhouse gas emissions, so they warm more than the previous ones”, Hofer says.
The study is published in Nature Communications.
“The Arctic warms more in the new models and this means that Greenland melts more. How much it melts depends on how much greenhouse gases we will emit in the future”, Hofer says to Titan.uio.no.
Increase from 10 to 18 centimeters
All climate models have scenarios for different levels of greenhouse gas emissions. In this way, the researchers can predict what will happen if emissions do not decrease and what will happen if we manage to limit emissions to varying degrees.
With very high emissions, meaning if everything continues like today, the previous models showed that the melting of the Greenland ice sheet will contribute to the oceans rising by about ten centimeters.
“The new models have 18 centimeters of global sea level rise by 2100”, Hofer says.
For medium-sized emissions, the old models said seven centimeters, while the new ones say ten centimeters. For low emissions, the figures are five and eight centimeters.
“The new middle emission scenario is as much as we previously thought of the high emission scenario”, Hofer says.
18 centimeters may not sound very threatening if your house or cottage is not right down on the beach. If the same is true for Antarctica, the situation will probably be different.
“Antarctica is ten times the size of Greenland. Most of the scary numbers come from some kind of collapse of parts of the Antarctic ice sheet”, Hofer says.
“The contribution to global sea level rise could potentially be tenfold".
Aiming magnifying glass at Greenland
When the Intergovernmental Panel on Climate Change (IPCC) publishes its sixth report in 2022, it will be with new and better models. These new models are used in the new study on the Greenland ice sheet.
“The new models have more physics, they have better representation of clouds, they have higher resolution, so they should in theory be more trustworthy”, Hofer says.
In total, the next IPCC report contains 30 climate models. Hofer and his colleagues have used eleven of them. The figures they present are an average of the selected models.
“There are some variations between the eleven models, but the new model with the least amount of melt still has more than the old models”, Hofer says.
Although the new ones are likely better than the old ones, the global climate models are relatively coarse-grained. They have to be for it to be possible to perform the enormous calculations. Hofer has zoomed in on Greenland to get a better picture of a smaller area.
“I think we are the first group to use those climate models and put these data into a very high resolution model just for Greenland. It’s basically a magnifying glass”, Hofer says.
With this magnifying glass, they bring out details about the surface on Greenland that disappear in the large models.
“You need a higher resolution to describe the areas on the edges because Greenland only melts along the edges”, Hofer says.
Now they want to find out why
So far, the researchers have not found the reasons why the new model melts more ice in Greenland.
“Now we need to find out why it melts more. Is it due to clouds? Is it due to ocean currents that are different in the new models? Is it due to the atmospheric pressure systems working in a different way?”
“This is just the starting point”, Hofer says.
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Stefan Hofer & al: Greater Greenland Ice Sheet contribution to global sea level rise in CMIP6, Nature Communications, December 2020.