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Carbon Dioxide Link Provides New Estimates of Ice-Free Summer

New research published this week shows a direct correlation between each metric ton of carbon dioxide emitted into the atmosphere and the amount of sea ice lost in the Arctic. 

Written by Véronique Morin Published on Read time Approx. 5 minutes
Arctic sea ice extent averaged 6.4 million square kilometres (2.5 million square miles) last month, the lowest October in the satellite record.NASA/Kathryn Hansen

The Paris Agreement on climate change enters into force today with commitments from countries to curb their carbon dioxide emissions in an effort to limit global warming to 2C (3.6F) or lower this century.

New research published November 3 in the journal Science shows a direct correlation between each metric ton of carbon dioxide (CO2) emitted into the atmosphere and the amount of sea ice lost in the Arctic.

In the analysis, scientists predict the Arctic Ocean will be free of ice during the summer months by about 2040, if we keep emitting CO2 at the same rate – 35 billion tons a year. It is the first research to show direct and linear correlations between CO2 emissions and its impact on Arctic sea ice.

Arctic Deeply spoke with the paper’s lead researcher, Dirk Notz, director of the Arctic sea ice research unit at the Max Planck Institute for Meteorology in Hamburg, Germany.

Arctic Deeply: What is the main finding of your paper?

Dirk Notz: It is the very striking and very simple relationship between CO2 emissions and Arctic sea ice loss. We have been able to show that for each ton of CO2 that a person emits on this planet there is 3 square meters (32.3 square ft) of sea ice melted in the Arctic.

Arctic Deeply: How were you able to achieve such a clean linear correlation?

Notz: We combined simulation models and observational records, and we basically started to plot CO2 emissions with sea ice loss. And we did the same with other models, which makes us certain that this is a robust relationship. We looked at averages of 30-year periods. So, we didn’t look at individual events because there are ups and downs on individual years. We focused on the long-term trends. And there, the linear relationship was very obvious.

Arctic Deeply: Why wasn’t this reported before?

For the first time, we are now able to derive the evolution of Arctic sea ice simply and directly from observational records, whereas in the past we tended to use model simulations.

We use observations of Arctic sea ice from ship and airplanes for the period 1953 to 1978, and from satellite from 1979 until today. These we correlated with available data on global CO2 emissions during that period.

Multiyear sea ice is on the decline in the Arctic.

Arctic Deeply: What do these results mean for future ice projections under a business-as-usual scenario where we continue to emit about 35 billion tons of CO2 annually?

Notz: The convenient thing about this finding is that it becomes straightforward to calculate at which amount of CO2 emissions Arctic sea ice will be gone in the summer. And that is another 1,000 billion tons of CO2 emissions.

Arctic Deeply: So according to this, under a business-as-usual scenario, all Arctic sea ice will have disappeared in the summer in less than 30 years. Is this correct?

Notz: Yes. This is exactly the same number … that we emit to reach the 2C (3.6F) global warming target [outlined in the Paris Agreement on climate change]. So once we have emitted these 1,000 billion tons of CO2, Arctic sea ice will be gone in the summer and we will have reached the 2-degree global warming target.

Arctic Deeply: There have been other predictions putting the end of summer sea ice in about 30 years. What is different with your prediction? Is it that we can adjust the endpoint more easily now?

Notz: With our study, we now show that it really is the total amount of emissions that determine when Arctic sea ice is gone. For current emission levels, the Arctic is ice-free in 25 to 30 years’ time, for lower emissions it will come later. And if we somehow manage to keep total future CO2 emissions well below 1,000 gigatons (billion tons), Arctic summer sea ice might be around for a very long time.

Arctic Deeply: What is the take home message for policymakers?

Notz: This paper is very strong in that it offers very clear guidance for any policy action to directly translate future CO2 emissions into the implied loss of Arctic sea ice. It is not up to us to tell policymakers what they should be doing, but it is up to us to tell them what the consequences of their actions will be.

Arctic Deeply: So it makes it easier to drive home certain aspects of climate change to policymakers, is this the intent?

Notz: Absolutely. That is one thing. The other thing is for individuals it is not easy for them to grasp the consequences of their actions. For example, driving your car for 2,000 miles [3,200km] results in the loss of 3 square meters [32 square ft] of Arctic sea ice. If you fly from London to New York and back, that is another 3 square meters of sea ice melted. I think it makes it much easier to grasp how we contribute to global warming.

Arctic Deeply: Considering your finding, are governments going in the right direction when it comes to curbing global warming?

Notz: From a scientific point of view, there is no right or wrong direction. However, if society decides that it wants to keep Arctic summer sea ice and thus avoid the negative consequences of, for example, extreme-weather events, current policy is probably moving too slowly. However, having said that, since the ratification of the Paris Agreement, there seems quite some acceleration in international agreements to curb CO2 emissions, so that gives me personally some hope that we will still be able to keep this landscape of sea ice up north.

Arctic Deeply: Why was this not done before?

Notz: I guess simply nobody had the idea to compare or to link directly CO2 to Arctic sea ice. And so, nobody ever did this calculation before.

Arctic Deeply: What gave you the idea?

Notz: It is really the urge to understand the linear relationship (that was published before) between global temperatures and Arctic sea ice. That is something that we have been seeing for quite a while in the models. That was the starting point of this paper: We tried to understand this linear relationship by exploring other factors such as CO2 and ended with these striking results that are so easy to convey.

Arctic Deeply: What are the other variables that are also important in Arctic sea ice that might disrupt that direct link between CO2 and Arctic sea ice, and that we might surpass?

Notz: Eventually, on century-long time scales the heat uptake by the ocean becomes important. Therefore, in our study we only focused on time scales of a few decades where the oceanic heat content is of minor importance for the evolution of Arctic sea ice.

This version corrects an earlier version of the story in which it was reported that one ton of carbon dioxide melted 1 square meter of Arctic sea ice. In fact, each ton of carbon dioxide emitted leads to the melting of 3 square meters of Arctic sea ice.

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