Higher sea level may come sooner than expected

By studying 120,000-year-old layers in the ice of Greenland, researchers have determined that the ice cover seems to be able to survive a warmer climate better than was previously believed. But at the same time they have found signs that the changes that are nevertheless happening will occur at an unexpectedly rapid rate. The level of the global seas may therefore rise faster than was previously thought.

One example of rapid change was found by scientists who were studying a so-called ice stream, ice that moves like a river through the rest of the inland ice and often forms icebergs at the mouth, so-called calving.

“In just two-three years the speed of a large ice stream nearly doubled. This means that we have underestimated the rapid changes that may ensue from the amounts of ice leaving the ice each year,” says Dorthe Dahl-Jensen, a professor at the Niels Bohr Institute at Copenhagen University. Dorthe Dahl-Jensen is taking part this week in the climate conference “Global Environmental Change: The Role of the Arctic”, arranged by the European Science Foundation, the Swedish Research Council, and the Research Council Formas (Sweden).

Dorthe Dahl-Jensen’s research also indicates that the inland ice can cope with a warmer climate considerably better than previous models calculated. Dorthe Dahl-Jensen and her colleagues are now updating the base for these models, for example by studying how ice moved during the so-called Eem Warm Period.

During the Eem Period, some 120,000 years ago, it was on average several degrees warmer than at present. This warmer climate lasted many thousand years. Scientists have been able to determine this using some dozen parameters, including the oxygen content of the ice. They have also taken DNA samples from under the ice cover. The DNA samples show that it was about 400,000 years ago that inland Greenland was last bare ground. By combining these data, Dorthe Dahl-Jensen has created an updated model that shows that a great deal of the inland ice can remain in place even through a long period of warmer climate than we have had had in modern times thus far.

“We are now approaching the climate and the temperatures that prevailed during the Eem Period,” says Dorthe Dahl-Jensen. “In other words, this research is not about abstract reasoning but rather about something that may soon be a concrete reality. The advantage of researching the inland ice is that we can study how the ice was actually impacted by earlier warm periods and compare this to the models we have for calculating what the future ice cover might look like. If the model fits the Eem Period, then I can rely on the model.”

Dorthe Dahl-Jensen stresses the importance of having reliable models when researchers present their forecasts to politicians and the general public.

“We scientists mustn’t be ‘fortune-tellers’; we have to be ‘sages.’ We must absolutely not use models that exaggerate the dangers of climate change. We would lose all credibility. That is precisely why this type of research is crucial, since it can be used to confirm or modify the models we researchers present to society.