14 September 2016

The difficulty of predicting an ice-free Arctic

Posted by Nanci Bompey

By Trent Knoss

Blue sky begins to break through the clouds over Arctic Ocean ice Sept. 9, 2009. Blue sky begins to break through the clouds over Arctic Ocean ice. Credit: Patrick Kelley / U.S. Geological Survey

Blue sky begins to break through the clouds over Arctic Ocean ice.
Credit: Patrick Kelley / U.S. Geological Survey

The Arctic is nearing its seasonal sea ice minimum this month, but predicting exactly when the region will see its first ice-free summer may be more difficult than previously believed, according to new research.

After examining both high- and medium-level carbon dioxide emission modeling scenarios for the rest of the 21st century, the study found that it is not possible to reduce the uncertainty window for an ice-free Arctic to a period of less than 21 years due to the inherently chaotic nature of the climate.

The study also found that commonly-used metrics of past and present sea ice thickness, extent and volume are not predictive enough to reduce this long-range uncertainly further.

The new findings were published online today in the American Geophysical Union journal Geophysical Research Letters.

Scientists typically define an “ice-free Arctic” as having fewer than 1 million square kilometers worth of ice cover, which would leave the Arctic Ocean virtually clear while some pockets of ice would remain in the northern reaches of Canada and Greenland.

“When it comes to predicting the timing of an ice-free Arctic, climate models show a large spread of over 100 years. Many studies have attempted to narrow this wide range, in some cases to as little as five years,” said Alexandra Jahn, an assistant professor in the University of Colorado Boulder’s Department of Atmospheric and Oceanic Sciences (ATOC) and lead author of the new research. “Here, however, we find that the low bound of our predictive ability is significantly longer due to inherent climate variability.”

The study, which employed a large collection of simulations from the Community Earth System Model developed by the University Corporation for Atmospheric Research (UCAR) in Boulder, Colorado, also found that consecutive ice-free summers would become common after 2060 under the high emission scenario while remaining the exception in the medium emission scenario.

“Overall, these results serve as a sort of caution against over-narrowing the long-term sea ice predictions from climate models” said Jahn, who is also a fellow in CU Boulder’s Institute for Arctic and Alpine Research (INSTAAR).

Co-authors of the new research include Jennifer Kay of ATOC and a fellow at the Cooperative Institute for Research in Environmental Sciences at CU Boulder; Marika Holland of the Climate and Global Dynamics Laboratory at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado; and David Hall of CU Boulder’s Department of Computer Science.

— Trent Knoss is a science writer at CU Boulder. This post originally appeared as a press release on the CU Boulder website.