ATMOSPHERIC IMPACTS OF A SHRINKING ARCTIC SEA ICE COVER

Since the beginning of the modern satellite record in October 1978, the extent of Arctic sea ice has declined in all months, with the strongest downward trend at the end of the melt season in September. Recently the September trends have accelerated. Through 2001, the extent of September sea ice was decreasing at a rate of -7 per cent per decade. By 2006, the rate of decrease had risen to -8.9 per cent per decade. In September 2007, Arctic sea ice extent fell to its lowest level recorded, 23 per cent below the previous record set in 2005, boosting the downward trend to -10.7 per cent per decade. Ice extent in September 2008 was the second lowest in the satellite record. Including 2008, the trend in September sea ice extent stands at -11.8 percent per decade. Compared to the 1970s, September ice extent has retreated by 40 per cent, an area roughly comparable to the size of the United States east of the Mississippi River. Summer 2009 looks to repeat the anomalously low ice conditions that characterized 2007 and 2008.

The decreases in sea ice extent are best explained by a combination of natural variability (including changes in atmospheric and oceanic temperature and circulation) and rises in surface air temperatures linked to increasing concentrations of greenhouse gases in the atmosphere. Climate models that incorporate the effects of greenhouse gas emissions from fossil fuel burning show declining September ice extent over the period of observations., However, the model simulations mostly show smaller decreases in sea ice extent than has been observed. This argues that the models are too conservative, and that ice-free summers might be realized as early as the 2030s.

The continued decline of Arctic summer sea ice extent will affect heating in the lower atmosphere and, as a result, atmospheric circulation. These changes will influence temperature and precipitation patterns that affect transportation, agriculture, forestry, and water supplies. This talk summarizes the current and future predicted rates of ice loss and discusses the impacts these ice losses will have on atmospheric temperature and precipitation in the northern hemisphere.