Even if we stop emitting greenhouse gases today, there is a good chance that the Greenland ice sheet will continue to melt well beyond the year 2100.

Researchers come to this cautious conclusion in the magazine PLOS ONE. They are based on a computer model that can simulate the impact of climate change on the Greenland ice sheet. Using this model, the researchers mapped the Greenland ice sheet’s response to current climate change and past climate changes (which occurred over the past 125,000 years).

Very slow

The simulations indicate that the times when the Greenland ice sheet reached its minimum and maximum extent over the past 125,000 years often occurred thousands of years after temperatures in Greenland reached record highs or depths, respectively. Apparently, the Greenland ice sheet is very slow to respond to changes in climate. So slow, in fact, that it regularly happens that the Greenland ice sheet is still adjusting to the previous one when a new climate change occurs.

Small changes, big (delayed) effect

“It was already known in itself that ice sheets in general react very slowly to climate change,” says researcher Lennert Stap, affiliated with Utrecht University. “But what did surprise me was that even the geologically small changes in temperature and precipitation during the Holocene produced such long-lasting effects. For example, the Greenland ice sheet did not start to shrink until late in the 20th century, while the climate warming that prompted this started already around 1850 – the beginning of the industrial age.”

Strikingly enough, the fact that the ice sheet did not respond to warming until late in the 20th century can partly be traced back to a change in the climate that took place thousands of years earlier, to which the Greenland ice sheet also reacted very slowly. “According to our simulations, in 1850 the Greenland ice sheet was still fully adapting to the climatic cooling after the Holocene Thermal Maximum (about 8,000 years ago),” Stap explains. Scientias.nl. So the ice sheet was growing. “As a result, it took until the end of the 20th century for anthropogenic climate changes to become so strong that the Greenland ice sheet began to shrink.”

The ice cap is still melting

In other words, the changes the Greenland ice sheet is currently undergoing are not only driven by current climate changes, but also influenced by climate changes that occurred thousands of years ago. And that has a very important implication. Because it means that we can expect that today’s warming will also have a delayed effect. “Now that the contraction is underway, it could last for millennia, well past the year 2100 when most climate and sea level projections cease. That could even be the case if we completely cut our greenhouse gas emissions tomorrow.”

Why does the ice sheet react so slowly?
According to Stap, it can take thousands of years for the Greenland ice sheet to fully adapt to a change in climate. “The Greenland ice sheet is huge. With a volume of about 3 million cubic kilometers, it would lead to a global-mean sea level rise of 7.4 meters if it were to melt completely. In addition, the ice sheet is not an isolated system, there are important feedback loops between ice changes and the climate. If the ice sheet adapts to climate change, this could lead to new climate change, and thus set in motion a chain of changes.” And that probably doesn’t just apply to the Greenland ice sheet. “The Greenland ice sheet is certainly not unique in this regard,” says Stap. “The Antarctic ice sheet is even larger, about 8 times the volume on Greenland. A recent research colleagues and myself have shown that during the Early and Middle Miocene (23 to 14 million years ago), when it may have been even smaller and highly variable in volume, the Antarctic Ice Sheet could also sometimes be thousands to tens of thousands of years behind the Earth. climate.”

The finding that the Greenland ice sheet responds to climate change with a delay and that the effects of different climate changes sometimes even overlap, also influences the way in which the Greenland ice sheet should be studied, Stap argues. For example, it means that researchers who want to predict the future of the Greenland ice sheet must look further back and ahead. “Technically, that slow response is especially important for the initialization of future projections of the Greenland ice sheet – the starting point. You cannot just assume that the current ice sheet is in balance with the climate, an assumption that is still sometimes used. Instead, it is better to simulate a full ice age cycle (approximately 130 thousand years) in the run-up to future projections. Also, the year 2100 is too early to capture the full effect of climate change, ice sheet changes will continue long after that.”

Whereas the earlier climate changes that Stap and colleagues included in their study had a natural cause, the situation is different for the current climate change. Today’s warming is caused by humans. And with that, the study also reveals that our actions today will affect the Greenland ice sheet for thousands of years to come. “We are only now at the beginning of a long period in which the Greenland ice sheet will adapt to the climate changes since the industrial age,” Stap emphasizes. And as far as he is concerned, it is an extra reason to reduce our emissions – and therefore the consequences that our great-great-great-grandchildren may still experience. “Once set in motion, these changes are hard to stop, so every kilogram of CO2 counts.”