Models Unreliable on Antarctic Ice Expansion Projections

by Anthony Ward on September 26, 2013

in Blog

New studies are raising doubts about the reliability of climate model forecasts. As far back as the 1970s, most climate models have anticipated a decline in Antarctic sea ice. However, instead of declining, Antarctic sea ice in 2013 has approached record levels not seen since the 1970s. Scientists are scrambling to find explanations for this anomaly, but one thing is clear – model projections are facing a crisis of credibility.  If actual conditions diverge from the predicted, then how can we trust the predictions? It seems we are as likely to arrive to the truth about the Earth’s future climate using models as we are from reading tea leaves or performing an augury to pagan gods.

In order to salvage their credibility, scientists have sought a variable to explain away the errors of their models – increased polar winds. According to a new study, increased polar winds have offset the effect of rising temperatures. Adjusting for higher polar winds, models were able to account for 80 percent of the increase in Antarctic ice cover. The author of the study, Dr. Jinlun Zhang, an Oceanographer at the University of Washington, describes the results:

“The polar vortex that swirls around the South Pole is not just stronger than it was when satellite records began in the 1970s, it has more convergence, meaning it shoves the sea ice together to cause ridging. Stronger winds also drive ice faster, which leads to still more deformation and ridging. This creates thicker, longer-lasting ice, while exposing surrounding water and thin ice to the blistering cold winds that cause more ice growth

While higher winds could be driving the increase in polar ice, the remaining 20 percent of the increase remains unaccounted. This suggests some other factor, or combination of factors, might be driving the decrease. Moreover, scientists admit they are uncertain why the models did not anticipate the increase in polar wind. Thus, the explanation for the model error is based on the admission the models were wrong about polar wind speed. If the models were wrong about polar wind speed, then criticism about model reliability still stands.

Accepting this explanation, however, raises another problem. According to the U.S. National Snow and Ice Cover Data Center, previous studies suggest increases in polar wind speed lead to a faster rate of sea ice melt. How can the wind both increase and decrease the extent of ice?

It is clear that models must be taken with a grain of salt. Scientists are often uncertain about the exact cause of long-term changes in the Earth’s climate. Numerous variables should be considered. As Zhang notes in the study,

Still unknown is why the southern winds have been getting stronger. Some scientists have theorized that it could be related to global warming, or to the ozone depletion in the Southern Hemisphere, or just to natural cycles of variability.

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