13 de mayo de 2020
Simulations suggest ice-free Arctic summers by 2050
Future of Arctic’s sea-ice cover depends on carbon dioxide emissions
A new analysis, using global climate models, predicts that most of the Arctic Ocean could become ice-free during summer by 2050. This new forecast, which used continuous and consistent satellite observations generated via ESA’s Climate Change Initiative, suggests that the future of the Arctic’s sea-ice cover critically depends on future carbon dioxide emissions.
Each year, Arctic sea ice goes through a seasonal cycle, growing in area and thickness through the cooler winter months before shrinking back again as temperatures rise in the spring and summer, with the minima occurring usually in September.
Since satellite-based measurements have begun in the 1970s, data show a trend of more ice melting away during summers and less new ice forming during winters. The daily Arctic sea-ice extent minimum in September 2019 was the second lowest in the 40-year satellite record.
In a recent study, published in Geophysical Research Letters, scientists from 21 research institutes simulated the evolution of Arctic sea-ice using 40 different global climate models. The models encompass various hypothetical scenarios, including trajectories based on the reduction of greenhouse gas emissions.
The study found that in most of the simulations, the Arctic Ocean is predicted to drop below 1 million sq. km (an area typically considered to be ice-free) in summers before 2050 – even if greenhouse gases are reduced significantly.
Project coordinator, Dirk Notz from the University of Hamburg, comments, “We are very surprised by these findings. Even if we reduce emissions substantially, keeping global warming levels below 2°C, Arctic sea ice will nevertheless disappear occasionally in summers before 2050.”
The loss of sea ice in the summer will have a profound impact on our environment – influencing ocean circulation and hastening the warming of the Arctic. As sea ice declines, the areas of open water absorb more heat leading to the increase of ocean temperatures – beginning a cycle of warming and melting.
Another finding from the study suggests that an ice-free Arctic in the winter months appears possible if carbon dioxide continues to be emitted at high levels. “This study illustrates the fact that cutting greenhouse gas emissions remains vital to prevent the worst impacts on the Arctic,” Professor Notz states.
Simulations in this study are compared data records of sea-ice concentrations from 1979 until present that were prepared by EUMETSAT’s Ocean and Sea Ice Satellite Application Facility and ESA’s Climate Change Initiative programme. The climate models come from the Coupled Model Intercomparison Project (CMIP6) which is working towards improving the major climate models to support the assessment of climate change.
Dirk continues, “The satellite record of sea-ice concentration was crucial for our analysis of CMIP6 model simulations. Without such a long-term consistent record of the real-world evolution of Arctic sea ice, we would not have been able to estimate the robustness of the model simulations.
“By allowing us to examine how well models simulate the real evolution of the sea-ice cover, records such as these, guide and inform our projections for the future.”
Thomas Lavergne, the Climate Change Initiatives sea ice project science lead, comments, “It was good to see that our sea ice data contributed to this work. Here we have an excellent example of collaboration between the ESA Climate Change and EUMETSAT’s Ocean and Sea Ice teams to deliver state-of-the-art satellite data records to the climate science community.”
The authors of the paper do add caution. Although the CMIP6 multi-model ensemble mean provides a more realistic estimate of the sensitivity of September Arctic sea-ice area to a given amount of anthropogenic CO2 emissions compared with earlier CMIP experiments, they highlight that most CMIP6 models still fail to simulate at the same time a plausible evolution of sea-ice area and of global mean surface temperature.