January 4, 2010

Lessons of the Ice

We have all heard over and over that the icecaps are melting, glaciers are retreating, and sea level is rising as ice around the world turns to liquid water. We have covered this topic many times in our essay series, but we revisit the ice issue given two recent and important publications in the science literature.

The first article of interest is in the prestigious Journal of Climate written by two atmospheric and earth scientists from Canada. The title of the article is “A five-year record of summer melt on Eurasian Arctic ice caps”, and we never thought we would have much interest in the piece given its five-year time frame. We were wrong.

Sharp and Wang were concerned with summer melt for the Arctic sub-regions shown in the map below, and they used satellite-based “scatterometer” data to assess the rates of melt in the study area. It is a complicated story, but basically, when liquid water is present in near-surface layers of snow and firn (compact snow), there is a sharp reduction in microwave backscatter received by the satellite. More basic, but similar, measurement techniques have been used since 1973 to estimate melt activity from satellites, and the methods appear to work with reasonable accuracy. For most of the Sharp and Wang article, maps and tables are presented for their five-year 2000-2004 study period, and the results are impressive.


Figure 1. Map of the Arctic showing the locations of Svalbard (A), Novaya Zemlya (B), Severnaya Zemlya (C), the Queen Elizabeth Islands (D), and Greenland (E) relative to the major Arctic Ocean current systems (from Sharp and Wang, 2009).

A section in the article entitled “Longer-term context” is where the action is for us! Sharp and Wang determined the relationship between 850 mb temperatures (atmospheric temperatures about 5,000 feet above sea level) and annual and June-August melt season duration. The results were excellent for the June – August period with correlation coefficients between temperature and snow melt duration ranging from 0.91 to 0.95 for various sub-regions shown on the map. Next, they used the known 850 mb temperatures from 1948-2005 to estimate melt duration in over the past six decades. To our surprise, they conclude “If we consider all discrete 5-yr periods (pentads) between 1950 and 2004, the 2000–04 pentad has the second longest mean predicted melt duration on Novaya Zemlya (after 1950–54), and the third longest on Svalbard (after 1950–54 and 1970–74) and Severnaya Zemlya (after 1950–54 and 1955–59).”

We cannot help but notice that the time of greatest melting was the pentad from 1950 to 1954. Is that curious or what? The Earth warmed from 1910 to the mid-1940s, cooled from mid-1940s to the mid-1970s, warmed from the mid-1970s to the late 1990s, and has not warmed or cooled over the most recent decade. The 1950 to 1954 pentad with the longest melt seasons happens to have occurred during a time of global cooling. The same can be said for the 1955-1959 and 1970-1974 pentads with long melt seasons. The 2000-2004 pentad has seen relatively large melt duration periods, but to suggest that it was caused by global warming is not consistent with the largest melt duration values occurring during a time of global cooling.

Next up, Indian geologist Ravinder Kumar Chaujar of the Wadia Institute of Himalayan Geology published a recent paper in Current Science of interest to us at World Climate Report. Chaujar investigated the retreats and advances of the Chorabari glacier located near the long-standing Kedarnath Temple in the Himalayan region. The author notes that “Two wall engravings of writings/poems dated AD 650 and 850, on the back boundary wall of the temple, discuss the beauty of the Kedarnath temple. There is no mention about snow/ice/glaciers in them. These findings suggest that there was no glacier during that period around the temple.” These dates precede the Medieval Warm Period and remind us that modern day glaciers in the region have certainly come and gone many times in the past, long before anyone could blame humans for glacial retreats.

But the warmth ended, and as stated by Chaujar, “We consider that glaciations in the region started during the mid-14th century, i.e. the beginning of the Little Ice Age”. The Chorabari glacier advanced at this time, and it appears to have gone through periods of advances and retreats. As the glacier would advance, it would bulldoze rocks at its terminus, and there would be no chance of lichens establishing themselves in the active rock zone. However, once the glacier would retreat, the rocks would be left behind, and lichens could then be established. A variety of lichenometric techniques are available to date when the lichens began to grow, and those dates would indicate when the glacier began to retreat. Chaujar determined that the retreat began 258 years ago; around 1748 AD warming at regional and possibly global scales caused the melting. However, we read “After the peak of the Little Ice Age, recession of the glacier was followed by its three major stages of advance and retreat as indicated by the four loops of terminal and lateral moraines of the glacier.”

Two major lessons come from this study. One, any argument that the Medieval Warm Period and Little Ice Age were confined to Europe is clearly not supported by the evidence from the Himalayan region. Two, glaciers have advanced and retreated many times in the past with absolutely no connection to humans and/or the atmospheric concentration of greenhouse gases. To suddenly pronounce that glaciers are responding to human activities seems to disregard their behavior during periods when human activities certainly had no impact whatsoever.

Glaciers around the world are generally experiencing a melt period at present and there is evidence of melting occurring in the Arctic. However, as seen in the Chaujar and Sharp and Wang articles, there is a lot more to the story when it comes to linking global warming to melting ice.

References:

Chaujar, R.K. 2009. Climate change and its impact on the Himalayan glaciers – a case study on the Chorabari glacier, Garhwal Himalaya, India. Current Science, 96, 703-708.

Sharp, M., and L. Wang. 2009. A five-year record of summer melt on Eurasian Arctic ice caps. Journal of Climate, 22, 133-145.




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