October 22, 2007

A million square miles of open water

A couple of weeks ago, New York Times science writer Andrew Revkin wrote a piece titled “Arctic Melt Unnerves the Experts” in which he described this year’s record low Arctic summer sea ice extent and the how the dramatic decline over last year had caught many sea-ice scientists by surprise. Revkin goes on to interview a variety of experts on the topic of sea ice, most of which realize that some (most) of the sea ice decline observed over the past several decades is likely related to anthropogenic changes to the earth’s climate, while admitting that undoubtedly, some natural (non-human-influenced) processes likely contributed to the decline as well.

Revkin starts out by noting “astonished by the summer’s changes [in ice extent], scientists are studying forces that exposed one million square miles of open water—six Californias—beyond the average since satellites started measurements in 1979.”

And then he continues:

Proponents of cuts in greenhouse gases cited the meltdown as proof that human activities are propelling a slide toward climate calamity.

Arctic experts say things are not that simple. More than a dozen experts said in interviews that the extreme summer ice retreat had revealed at least as much about what remains unknown in the Arctic as what is clear. Still, many of those scientists said they were becoming convinced that the system is heading toward a new, more watery state, and that human-caused global warming is playing a significant role.

For one thing, experts are having trouble finding any records from Russia, Alaska or elsewhere pointing to such a widespread Arctic ice retreat in recent times, adding credence to the idea that humans may have tipped the balance. Many scientists say the last substantial warming in the region, peaking in the 1930s, mainly affected areas near Greenland and Scandinavia.

Depending on what Revkin meant by “recent times,” perhaps we could help him out as to where he may look in order to find out some information indicating that “widespread Arctic ice retreat” has occurred without any human help. If Revkin meant “since satellites started measurements in 1979” then, he probably has that covered, but if by “recent” he meant within the past 100 years or so, then maybe we could suggest a few other avenues to investigate.

For instance, Dr. Andy Mahoney, a post-doc at CIRES/NSIDC is working on examining some evidence from Russian sea ice charts complied as far back as the early 1930s. Apparently, Dr. Mahoney is finding that some pretty large variations in sea ice extent have occurred across the 20th century, including a period of relatively low sea ice extent that pre-dated a relative increase in sea ice area that occurred just prior to the sea ice decline of the last several decades (those observed in the satellite era). While Dr. Mahoney notes that the early declines don’t appear to be quite as large as the current ones, it is possible that they set the stage for them in that there was not a complete recovery in the intervening period.

Here is how Dr. Mahoney’s research efforts to date were summarized in an Abstract for a seminar titled “Multidecadal Arctic Sea Ice Variability: Large scale changes and local impacts” that he gave about a month ago out in Boulder, CO:

Abstract: As the Arctic sea ice pack retreats to record-breaking minimum extents, it is increasingly important to be able to set these changes in a longer-term context, while also increasing our awareness of the impacts such changes have at the local level. Here, I present results from research carried out at the National Snow and Ice Data Center using a recently digitized set of sea ice charts provided by the Arctic and Antarctic Research Institute (AARI), St Petersburg, Russia. The earliest chart dates back to July 1933 making the AARI ice charts perhaps the longest-lived systematic sea ice record in existence. In addition, I examine these sea ice data in conjunction with equally long records of air temperature derived from meteorological station data.

Timeseries of air temperature and the extents of pack ice, multiyear ice and landfast ice extents reveal three distinct periods of variability over the last 8 decades: a period of warm winters and decreasing summer and fall sea ice extent (period A), followed by a cool period of stable or slightly increasing extent (period B) before a period of year-roundwarm temperatures and ice loss (period C). In magnitude and seasonality, the warming and ice loss during period C are more significant that those during period A. However, the Russian Arctic ice pack did not fully recover during period B, suggesting that the early 20th Century warming during period A may have preconditioned the Arctic for greater change in recent decades. At the end of period B, there is a rapid expansion of both first year and multi year ice extent, which may also have been a catalyst for the subsequent rapid changes in recent years.

Perhaps Revkin should look up Dr. Mahoney in his search for records pointing to large scale ice decline in recent times that extend beyond Greenland and Scandinavia.

Or, perhaps he could consult the writing of noted early to mid-20th century Arctic researcher Dr. Hans Ahlmann. Ahlmann wrote a number of papers describing climate changes taking place in the Arctic in the first half of the 20th century, often referring to the warm-up that occurred back then as a “climate improvement.” We have made mention of some of Ahlmann’s findings previously (see here or here, for example). But we have recently come across a booklet that he prepared to augment a speech that he gave before the American Geographical Society in the fall of 1952 on “Glacial Variations and Climate Fluctuations” that we found to particularly enlightening. In it, he describes observations of receding glaciers, and rising temperatures across many disparate regions of the Arctic, as well as describing changes in plant and animal behavior and range shifts that have accompanied the climate warming. In fact, the northern migration of codfish in the Atlantic brought the species into southern Greenland for the first time and seemingly ushered newfound prosperity into the region. Ahlmann quotes the Prime Minister of Denmark proclaiming “In the last generation changes that have had a decisive influence on all social life have occurred in Greenland. A new era has begun. These changes are primarily due to two circumstances. Firstly, the Greenland climate has changed, and with it Greenland’s natural and economic prospects.”

But more to the point, Ahlmann volunteered the following observations and commentary concerning changes in sea ice extent and thickness:

The thickness of the ice forming annually in the North Polar Sea has diminished from an average of 365 centimeters at the time of Nansen’s Fram expedition of 1893-96 to 218 centimeters during the drift of the Russian icebreaker Sedov in 1937-40. The extent of drift ice in Arctic waters has also diminished considerably in the last decades. According to information received in the U.S.S.R. in 1945, the area of drift ice in the Russian sector of the Arctic was reduced by no less than 1,000,000 square kilometers between 1924 and 1944. The shipping season in West Spitsbergen has lengthened from three months at the beginning of this century to about seven months at the beginning of the 1940s. The Northern Sea Route, the North-East Passage, could never have been put into regular usage if the ice conditions in recent years had been as difficult as they were during the first decades of this century.

Granted, one million square kilometers is not the same as Revkin’s one million square mile anomaly, but it is a healthy portion of it (~40%) and, it only pertains to the “Russian sector,” so, it is possible that additional declines occurred in other portions of the Arctic Ocean as well. Likely the source of Ahlmann’s comments and the source of Dr. Mahoney’s data are one and the same. But even so, they seem to provide tantalizing evidence that large-scale sea ice variations took place in Arctic sea ice extent prior to human alteration of the earth’s greenhouse effect.

Perhaps the revelation of this early Russian sea ice data will cause modern day ice researchers to scratch their heads even more than they are doing already when trying to understand the processes that are involved in controlling Arctic sea ice conditions.

Of course, this is not to say that human activity is not behind the current warm-up in the Arctic and the consequences that go along with it, but it is to say, that such climate fluctuations are likely not unique in the recent past and as such, probably don’t pose intractable conditions for the earth’s natural systems.

Reference:

Ahlmann, H. W., 1953. “Glacier Variations and Climatic Fluctuations”. Series Three, Bowman Lecture Series, The American Geographical Society, George Grady Press, New York, available from http://www.questia.com/PM.qst?a=o&d=1918470




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