Arctic Sea Ice Loss Strongly Linked to Rise in Greenhouse Gasses
03.05.2012 - Water & Oceans, Ice & Snow, Bi-polar
A new study conducted by scientists from the Max Plank Institute for Meteorology in Germany shows a strong, physically plausible correlation between rising concentrations of greenhouse gases in the atmosphere and diminishing sea ice in the Arctic.
Published in Geophysical Research Letters, the researchers decided to not use complex climate models to link a specific climate forcing to observed climatic change, as fluctuations in sea ice are too chaotic to be reproduced in standard climate models. Instead they too ka different approach: they used a historical record that described natural sea ice extent variations between the 1950s and 1970s and compared them to the magnitude of fluctuations in Arctic sea ice cover measured using satellites since the late 1970s.
The team’s findings show that it is very unlikely that extreme sea ice minima happened purely by chance, and they were able to rule out the possibility that a positive self-acceleration feedback could be the main driver of sea ice retreat. They also were able to rule out an increase in solar radiation as a possibility, as solar output has decreased over the past few decades, and they could find no plausible link between prevailing wind patterns, volcanic eruptions, heat transport via the ocean, or cosmic rays.
The only plausible driving mechanism turns out to be atmospheric greenhouse gas concentrations. Lead author Dr. Dirk Notz explained that greenhouse gasses increase downwelling thermal radiation, which plays a major role in the heat budget of the Arctic.
The story is not the same for the Antarctic, however, where sea ice extent has been slightly increasing recently. Greenhouse gasses are not the main driver, but rather by prevailing wind patterns. The difference lies in the fact that the Arctic and Antarctic have two different land distributions.
In the Arctic, the ice is locked by the surrounding landmasses. Its extent is governed by melting and freezing, a process over which greenhouse gas concentrations can have a major forcing influence. In the Antarctic, being a region with a continent surrounded by the open Southern Ocean, sea ice is free to drift about freely, which allows prevailing winds that circulate around Antarctica to have a greater influence on sea ice extent than greenhouse gasses.