Massive Exaggeration on Southern Alaskan Glacial ice melt

Paul Homewood has a lovely example of gross exaggeration on climate change. He has found the following quote from a University of Oregon study

Incessant mountain rain, snow and melting glaciers in a comparatively small region of land that hugs the southern Alaska coast and empties fresh water into the Gulf of Alaska would create the sixth largest coastal river in the world if it emerged as a single stream, a recent study shows.

Since it’s broken into literally thousands of small drainages pouring off mountains that rise quickly from sea level over a short distance, the totality of this runoff has received less attention, scientists say. But research that’s more precise than ever before is making clear the magnitude and importance of the runoff, which can affect everything from marine life to global sea level.

The collective fresh water discharge of this region is more than four times greater than the mighty Yukon River of Alaska and Canada, and half again as much as the Mississippi River, which drains all or part of 31 states and a land mass more than six times as large.

“Freshwater runoff of this magnitude can influence marine biology, near shore oceanographic studies of temperature and salinity, ocean currents, sea level and other issues,” said David Hill, lead author of the research and an associate professor in the College of Engineering at Oregon State University.

“This is an area of considerable interest, with its many retreating glaciers,” Hill added, “and with this data as a baseline we’ll now be able to better monitor how it changes in the future.” (Bold mine)

This implies that melting glaciers are a significant portion of the run-off. I thought I would check this out. From the yukoninfo website I find

The watershed’s total drainage area is 840 000 sq. km (323 800 sq. km in Canada) and it discharges 195 cubic kilometres of water per year.

Therefore the runoff is about 780 cubic kilometres per year.

From Wikipedia I find that the Mississippi River has an average annual discharge of 16,792 m3/s. This implies the average discharge into the Gulf of Alaska is about 25,000 m3/s. This equates to 90,000,000 m3 per hour or 2,160,000,000 m3 per day. That is 2.16 cubic kilometres per day, or 788 cubic kilometres per year. If this gross runoff was net, it would account for two thirds of the 3.2mm sea level rise recorded by the satellites. How much of this might be from glacial ice melt? This is quite difficult to estimate. From the UNIPCC AR5 WGI SPM of Sept-13 we have the following statement.

Since the early 1970s, glacier mass loss and ocean thermal expansion from warming together explain about 75% of the observed global mean sea level rise (high confidence). Over the period 1993 to 2010, global mean sea level rise is, with high confidence, consistent with the sum of the observed contributions from ocean thermal expansion due to warming (1.1 [0.8 to 1.4] mm yr–1), from changes in glaciers (0.76 [0.39 to 1.13] mm yr–1), Greenland ice sheet (0.33 [0.25 to 0.41] mm yr–1), Antarctic ice sheet (0.27 [0.16 to 0.38] mm yr–1), and land water storage (0.38 [0.26 to 0.49] mm yr–1). The sum of these contributions is 2.8 [2.3 to 3.4] mm yr–1. {13.3}

How much of this 0.76 mm yr–1 (around 275 cubic kilometres) is accounted for by Southern Alaska?

The author of the Oregon study goes onto say.

This is one of the first studies to accurately document the amount of water being contributed by melting glaciers, which add about 57 cubic kilometers of water a year to the estimated 792 cubic kilometers produced by annual precipitation in this region.

That is 20% (range 14-40%) of the global glacial ice melt outside of Greenland and Iceland is accounted for by Southern Alaska. Northern and Central Alaska, along with Northern Canada are probably far more significant. The Himalayan glaciers are huge, especially compared to the Alps or the Andes which are also meant to be melting. There might be glaciers in Northern Russia as well. Maybe 1%-10% of the global total comes from Southern Alaska, or 3 to 30 cubic kilometres per annum, not 14-40%. The Oregon Article points to two photographs on Flikr (1 & 2) which together seem less than a single cubic kilometre of loss per year. From Homewood’s descriptions of the area, most of the glacial retreat in the area may have been in the nineteenth and early twentieth centuries.

Maybe someone can provide a reconciliation that will make the figures stack up. Maybe the 57 cubic kilometres is a short-term tend – a sibgle year even?

Kevin Marshall

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