It's raining on the Greenland ice—in the winter

It's raining on the Greenland ice -- in the winter
Increasing rainfall over the Greenland ice sheet is driving rapid melting of the surface. Here, researchers cross Greenland's Russell Glacier, July 2018. Credit: Kevin Krajick/Earth Institute

Rainy weather is becoming increasingly common over parts of the Greenland ice sheet, triggering sudden melting events that are eating at the ice and priming the surface for more widespread future melting, says a new study. Some parts of the ice sheet are even receiving rain in winter—a phenomenon that will spread as climate continues to warm, say the researchers. The study appears this week in the European scientific journal The Cryosphere.

Greenland has been losing ice in recent decades due to progressive warming. Since about 1990, average temperatures over the have increased by as much as 1.8 degrees C (3.2F) in summer, and up to 3 degrees C (5.4F) in winter. The 660,000-square-mile sheet is now believed to be losing about 270 billion tons of ice each year. For much of this time, most of this was thought to come from icebergs calving into the ocean, but recently direct meltwater runoff has come to dominate, accounting for about 70 percent of the loss. Rainy weather, say the study authors, is increasingly becoming the trigger for that runoff.

The researchers combined with on-the-ground weather observations from 1979 to 2012 in order to pinpoint what was triggering melting in specific places. Satellites are used to map melting in real time because their imagery can distinguish snow from . About 20 automated weather stations spread across the ice offer concurrent data on temperature, wind and precipitation. Combining the two sets of data, the researchers zeroed in on more than 300 events in which they found the initial trigger for melting was weather that brought rain. "That was a surprise to see," said the study's lead author, Marilena Oltmanns of Germany's GEOMAR Centre for Ocean Research. She said that over the study period, melting associated with rain and its subsequent effects doubled during summer, and tripled in winter. Total precipitation over the ice sheet did not change; what did change was the form of precipitation. All told, the researchers estimate that nearly a third of total runoff they observed was initiated by rainfall.

Melting can be driven by a complex of factors, but the introduction of liquid water is one of the most powerful, said Marco Tedesco, a glaciologist at Columbia University's Lamont-Doherty Earth Observatory and coauthor of the study. Warm air, of course, can melt ice directly, but is not very efficient by itself, he said. However, can produce cascading effects. One is that they make it more likely that atmospheric conditions will pass the threshold where precipitation comes down as rain, not snow. Liquid water carries a great deal of heat, and when it soaks into a snowy surface, it melts the snow around it, releasing more energy. Meanwhile, the warm air that brought the rain often forms clouds, which hem in the heat.

This combination of factors produces a pulse of melting that feeds on itself, and well outlasts the rain itself, often by several days. Furthermore, the scientists found that the length of these pulses increased over the decades they analyzed, in cold weather from two days to three, and in the brief summer, from two days to five.

It's raining on the Greenland ice -- in the winter
Summer runoff from melting ice near Kangerlussuaq, Greenland. Credit: Kevin Krajick/Earth Institute

There are longer-term effects, say the study authors. They believe that part of the meltwater runs off, but the rest refreezes in place, morphing normally fluffy, reflective snow on or near the surface into darker, denser masses of ice. This ice absorbs solar radiation more easily than snow, so when the sun comes out, it melts more easily, producing more liquid water, which feeds more melting, in a vicious feedback loop. This, said Tedesco, has led to more and earlier melting in the summer. And because the surface has been hardened into ice, much of that meltwater can more easily flow off the ice sheet toward the sea.

"If it rains in the winter, that preconditions the ice to be more vulnerable in the summer," said Tedesco. "We are starting to realize, you have to look at all the seasons."

While rain is hitting increasingly far-flung parts of the ice in summer, winter rainfall so far appears mostly confined to lower elevations in south and southwest Greenland. It is brought in by moist, relatively warm ocean winds from the south, which some communities in other areas call neqqajaaq. These winds may be getting more common due to climate-induced shifts in the jet stream. The elevation of the ice sheet increases further inland and it is thus colder and snowier there; but if continue to increase as expected, the line where the moisture comes down as rain instead of snow will rapidly move inward, upward and northward. "The ice should be gaining mass in winter when it snows, but an increasing part of the mass gain from precipitation is lost by melt," said Oltmanns.

Greenland is not the only place in the far north affected by increasing . In recent years, anomalous winter rains have hit the northern Canadian tundra, then refrozen over the surface, sealing in plants that caribou and musk oxen normally forage through the loose snow; in some years, this has decimated herds. And a just-published study from near Fairbanks, Alaska, shows that increasing spring rains are percolating down through the permafrost, thawing it and releasing large amounts of methane, a highly efficient greenhouse gas.

Between 1993 and 2014, global sea-level rise accelerated from about 2.2 millimeters a year to 3.3 millimeters, and much of that acceleration is thought to be due to melting in Greenland. Projections of sea-level rise for the end of this century generally range from two to four feet, but most projections do not yet account for what may happen to the ice in Greenland, nor with the much larger mass in Antarctica, because understanding of the physics is still not advanced enough.

Richard Alley, a prominent glaciologist at Pennsylvania State University, said that the new paper adds to the understanding. "The big picture is clear and unchanged," he said. "Warming melts ice," But, he added, the specific processes that will carry this "need to be quantified, understood and incorporated into models. This new paper does important work understanding and quantifying."


Explore further

How the Greenland ice sheet fared in 2018

More information: "Increased Greenland melt triggered by large-scale, year-round cyclonic moisture intrusions," The Cryosphere (2019).
Citation: It's raining on the Greenland ice—in the winter (2019, March 7) retrieved 20 June 2019 from https://phys.org/news/2019-03-greenland-icein-winter.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
326 shares

Feedback to editors

User comments


Mar 08, 2019
Wouldn't it be fantastic if Greenland were to become green again? At the expense of welfare crapholes like New Orleans? Too bad man-made global warming is a myth.

Mar 08, 2019
More Pathological LIES from the Pathological "science", of the AGW Cult.

https://rmets.onl.../joc.852

Mar 08, 2019
haw haw , guess it depends on your definition of winter ,, this one is real cold

https://www.windy...pressure

Mar 09, 2019
"Wouldn't it be fantastic if Greenland were to become green again?" - Moron

Where do you intend to get the required soil, Moron?

Mar 09, 2019
Between 1993 and 2014, global sea-level rise accelerated from about 2.2 millimeters a year to 3.3 millimeters

No it didn't. That is a gross misreprsentation of the data. There has been no appreciable acceleration in sea level rise in the last 25 years.

The 2.2 mm/yr rate comes from tide gauge measurements, with records going back to 1870. The 3.3 mm/yr rate comes from satellites starting in 1993. No one is certain why there's a discrepancy in the two datasets, but you can see from this graph of both that there was no sudden jump in rate where they overlap between 1993 and 2013.

https://climate.n...a-level/

And the satellite rate was 3.4 mm/yr but has declined slightly to 3.2 mm/yr which means, according to the satellite data, that sea level rise has been slowing.

Mar 09, 2019
< a typical summers day in winter in this green and pleasant land >

What with rain in southern Greenland
the Eskimos are experiencing
the monsoon season earlier in their green and pleasant land
the problem the Eskimos are now facing
as
they
watch the approaching masts
of the Viking long ships
they
now have this problematic problem
as
these Vikings
just like last time
are not prepared
fore this green and pleasant lands fickle weather
for although
the ice appears to be melting
for although
it appears to be raining
even though
these Vikings in days gone by grew crops
please
feel free to visit this Greenland
because
on a good day
when there breezes are light
the sun is in the blue sky
it
is freezing
as
not the freezing any mortal man experiences
but
FREEZING as in MINUS 60° with a WIND CHILL of MINUS 100°

Mar 09, 2019
"Wouldn't it be fantastic if Greenland were to become green again?" - Moron

Where do you intend to get the required soil, Moron?


or the sunlight?

The "global warming is good argument" ignores the fact that far northern and southern latitudes get significantly less annual horizontal irradiance. Less irradiance lower yields.

https://globalsol...1.300489

Mar 09, 2019
''Where do you intend to get the required soil, Moron? ''

My newfoundland ancestors had the same problem , they used seaweed .

@ granville ,, LOL ! a good one

Mar 09, 2019
GREENLAND - This Green and Pleasant Land
snoosebaum> ''Where do you intend to get the required soil, Moron? ''
My newfoundland ancestors had the same problem , they used seaweed .
@ granville ,, LOL ! a good one

When in the height of summer
blazing June
when the temperatures are in single figures
as in Eskimo temperatures
this implies
any temperature between MINUS 9° and PLUS 9°
as these single digit temperatures
to these hardy Eskimo's
these hardy Eskimo's run down their duck board on the melting permafrost
dress down to their swimming trunks
go swimming amongst the melting ICE BURGS
then relax on the beach achieving that healthy golden brown tan
all in temperatures just above freezing
on those rare summer heat waves
as at any moment
the clouds roll in
the wind picks up
then the fun is over
and so is this brief few minutes in the sun
as the temperature
once again
Drops to MINUS 60° with a WIND CHILL of MINUS 100°

Mar 09, 2019
From all this endless alarmist BS, you'd think Miami would be underwater by now.

V4: why isn't Miami underwater by now? Moron.

Mar 09, 2019
From all this endless alarmist BS, you'd think Miami would be underwater by now.

V4: why isn't Miami underwater by now? Moron.


Please link to the study that said Miami would be underwater by 2019. Otherwise you are making things up.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more