Global Sea Ice on the Rebound?

While the retreat of ice at the Earth’s poles has been visible and effective evidence in support claims of catastrophic climate change, global sea ice has been on the rebound in recent months.  Sea ice has quickly re-taken previously thawed regions of the ocean at both ends of the globe, according to satellite observations recently published by NOAA’s National Snow and Ice Data Center.

While global sea ice extent has only been measured with high resolution since 1979, the recent increase in sea ice coverage now puts the start of 2009 in the same place as the year when records started:  1979.  While the extent of sea ice in the northern hemisphere is currently slightly below the 30-year mean, the coverage in the southern hemisphere exceeds the thirty-year mean by approximately 500,000 square kilometers.  While some scientists argue this is a clear and obvious sign of catastrophic global warming, others have urged restraint.  They argue this data cannot be reliably compared to older historical records that had less resolution and reliability.

The North Pole

Early in the northern hemisphere summer, the rate of sea ice melt painted a grim picture of the upcoming winter season.  Some even predicted that there would be enough open water that one could sail to the north pole.  Such predictions failed when the seasonal sea ice minimum was reached on September 12, 2008 and the arctic was still covered by 1.74 million square miles of ice.  Since mid-September, arctic sea ice has been growing in response to the normal seasonal cooling.

While the rate of ice growth has since slowed from the near-record rates of October and November, the NSIDC data points to a logical conclusion:  The polar ice is simply running out of physical room to expand as the surface area of open water shrinks as ice fills it.  While the rate has slowed over the last month, the rapid early season growth meant that the arctic has experienced a greater extent of sea ice than most of the 2007-08 winter season.  The recent slowing in growth now puts this season roughly on par with last year at this time with roughly 13 million square kilometers of ice covering the region.

The South Pole

For approximately 9 of the last 12 months, the extent of sea ice covering the South Pole has been equal to or greater the 30-year average.  The southern hemisphere is now in the midst of the summer season and thus sea ice coverage is in a normal but temporary rapid decline.  However, even during this period of normal melting, the Antarctic sea ice still remains more expansive than the 30-year average, according to data from the Arctic Climate Research Center at the University of Illinois.

Not only has this season’s ice coverage exceeded the 30-year average, the extent of sea ice over Antarctica has actually been steadily growing over the last 20 years.  While some may see this as evidence in direct opposition to global warming trends, NASA-funded research from 2005 indicates that expanding Antarctic ice may actually be proof positive of such warming (Warmer air may cause increased antarctic sea ice cover).  “Most people have heard of climate change and how rising air temperatures are melting glaciers and sea ice in the Arctic,” said Dylan C. Powell, lead author of the paper and a doctoral candidate at the University of Maryland Baltimore County. “However, findings from our simulations suggest a counterintuitive phenomenon. Some of the melt in the Arctic may be balanced by increases in sea ice volume in the Antarctic.”

Climate Change Models

While much of the northern hemisphere sea ice melting has been relatively well-handled by global climate models, the antarctic ice expansion has been under-resolved by the models.  Such disparities raise several questions concerning the reliability of such computer models of the climate.  Such disparity would not have been significant in the early days of computer climate modelling, as such models were only seen as one indication of potential trends.  Today, however, as climate change is bringing about legislative and regulatory action, the accuracy and reliability of model output is increasingly important.  While the 3o-year spans examined by the satellite data of both the northern and southern hemisphere is insightful in its detail and short-term trend indications, it is worth noting what a short span of time these data represent in the context of geologic time.