https://www.theguardian.com/environment/2019/jan/18/north-america-glacier-melt-study-climate-change
[images and links in online article]
North American glaciers melting much faster than 10 years ago – study
Satellite images show glaciers in US and Canada, excluding Alaska, are
shrinking four times faster than in previous decade
Glaciers in western North America, excluding Alaska, are melting four
times faster than in the previous decade, with changes in the jet stream
exacerbating the longer-term effects of climate change, according to a
new study.
The retreat hasn’t been equal in the US and Canada. The famous alpine
ice masses in the Cascade Mountains in the north-west US have largely
been spared from the trend.
“The losses we would expect were reduced because we got a lot of
additional snow,” said David Shean, a co-author at the University of
Washington. “Moving forward we may not be so lucky.”
When the ice melts: the catastrophe of vanishing glaciers
Read more
The jet stream – the currents of fast-flowing air in the atmosphere that
affect weather – has shifted, causing more snow in the north-western US
and less in south-western Canada, according to the study released in
Geophysical Research Letters, a publication of the American Geophysical
Union. Changes in the northern hemisphere jet stream are increasingly
firmly linked to global warming.
That warming from humans burning fossil fuels is also expected to
continue to melt alpine glaciers, even under scenarios for more moderate
greenhouse gas levels.
While some of the fourfold increase in the melting rate in western North
America is related to manmade climate change, the researchers can’t say
with certainty how much.
“We’re starting to understand these shorter cycles that have real
impacts on how the glaciers are behaving and how much water is stored in
the glaciers,” Shean explained.
Alaskan glaciers get much of the attention in North America because
Alaska is warming faster than the continental US. Mount Hunter in Denali
national park, is seeing 60 times more snow melt than it did 150 years ago.
The North American glaciers analyzed in the new study are far smaller
than those in Alaska, Asia and elsewhere, so they won’t contribute much
to sea-level rise as they melt. The authors say they offer critical
lessons for water management, fisheries and flood prevention.
With shrinking glaciers, less water will be available for nearby river
systems when rainfall is low. In some parts of the world, millions of
people could lose their primary water supplies.
In the Pacific north-west US, if glaciers melted entirely, that could
reduce the flow of certain watersheds by up to about 15% in dry months
of August and September, Shean said.
“In our case that will have an impact, especially if we’re having a
drought year … but in general at least for the foreseeable future we
should be OK here in Washington,” he said.
Snow pack changes will be more important than glacier melt for water
planners in the western US, Shean said.
Still, changes in water temperature could pose problems for fish. And
the sediment that comes with melting glaciers could fall to the bottoms
of riverbeds, making them overflow during heavy rains.
The authors got their data by comparing satellite images of glaciers
from 2000 to 2009 and from 2009 to 2018. They estimated elevation
changes, which can be difficult to assess with the smallest glaciers.
Other researchers are attempting to get spy satellite and aerial photos
from the 1950s and 1960s declassified so they can study longer-term
changes, Shean said.