RUSSIA
BEAUFORT SEA
PERMAFROST
ALASKA
CANADA
BERING
SEA
GULF OF
ALASKA
Alaska’s permafrost, shown here in 2010, is no longer permanent. It is starting to thaw.
By 2050, much of this frozen ground, a storehouse of ancient carbon, could be gone.
This is what may be lost.
YUKON DELTA NATIONAL WILDLIFE REFUGE, Alaska —
The Arctic is warming about twice as fast as other parts of the planet,
and even here in sub-Arctic Alaska the rate of warming is high. Sea ice
and wildlife habitat are disappearing; higher sea levels threaten
coastal native villages.
But to the scientists from Woods Hole Research Center
who have come here to study the effects of climate change, the most
urgent is the fate of permafrost, the always-frozen ground that
underlies much of the state.
Starting just a few feet below the surface
and extending tens or even hundreds of feet down, it contains vast
amounts of carbon in organic matter — plants that took carbon dioxide
from the atmosphere centuries ago, died and froze before they could
decompose. Worldwide, permafrost is thought to contain about twice as
much carbon as is currently in the atmosphere.
Once this ancient organic material thaws,
microbes convert some of it to carbon dioxide and methane, which can
flow into the atmosphere and cause even more warming. Scientists have estimated
that the process of permafrost thawing could contribute as much as 1.7
degrees Fahrenheit to global warming over the next several centuries,
independent of what society does to reduce emissions from burning fossil
fuels and other activities.
Stash Wislocki
In Alaska, nowhere is permafrost more
vulnerable than here, 350 miles south of the Arctic Circle, in a vast,
largely treeless landscape formed from sediment brought down by two of
the state’s biggest rivers, the Yukon and the Kuskokwim. Temperatures
three feet down into the frozen ground are less than half a degree below
freezing. This area could lose much of its permafrost by midcentury.
That, said Max Holmes, senior scientist and
deputy director of the research center, “has all kinds of consequences
both locally for this region, for the animals and the people who live
here, as well as globally.”
“It’s sobering to think of this magnificent
landscape and how fundamentally it can change over a relatively short
time period,” he added.
Max Holmes, deputy director and senior scientist of the Woods Hole Research Center.
Stash Wislocki
But on this wide, flat tundra, it takes a practiced eye to see how Alaska is thawing from below.
At one of the countless small lakes that
pepper the region, chunks of shoreline that include what had been
permafrost have calved off toward the water.
Nearby, across a spongy bed of mosses and
lichens, a small boggy depression likely formed when the ice in the top
layers of the permafrost below it melted to water.
John Schade
John Schade
In July, the Woods Hole scientists, along with 13 undergraduate and graduate students working on projects of their own,
set up a temporary field station on a nameless lake 60 miles northwest
of Bethel, which with a population of 6,000 is the largest town in the
region. They drilled permafrost cores with a power auger, took other
sediment and water samples and embedded temperature probes in the frozen
ground. Later, back in the lab at Woods Hole, they began the process of
analyzing the samples for carbon content and nutrients.
The goal is to better understand how thawing
permafrost affects the landscape and, ultimately, how much and what mix
of greenhouse gases is released.
“In order to know how much is lost, you have
to know how much is there,” said Sue Natali, a Woods Hole scientist and
permafrost expert.
Even in colder northern Alaska, where
permafrost in some parts of the North Slope extends more than 2,100 feet
below the surface, scientists are seeing stark changes. Vladimir E.
Ramonovsky, a permafrost researcher at the University of Alaska,
Fairbanks, said that temperatures at a depth of 65 feet have risen by 3
degrees Celsius (about 5.5 degrees Fahrenheit) over decades.
Near-surface changes have been even greater.
At one northern site, he said, permafrost temperatures at shallow depths
have climbed from minus 8 degrees Celsius to minus 3.
“Minus 3 is not that far from zero,” Dr.
Romanovsky said. If emissions and warming continue at the same rate, he
said, near-surface temperatures will rise above freezing around the
middle of the century.
Max Holmes and Sue Natali of the Woods Hole Research Center.
Stash Wislocki
There is plenty of debate among scientists
about when and how much of Alaska’s permafrost will thaw. And there is
no doubt that thawing of the full depth of permafrost would take
millenniums.
But Dr. Romanovsky said that his and others’ work shows that permafrost “is not as stable as people thought.”
In addition to greenhouse gas emissions,
thawing wreaks havoc on infrastructure, causing slumping of land when
ice loses volume as it turns to water.
The main road in Bethel, where average
temperatures have risen about 4 degrees Fahrenheit since the mid-20th
century, is more of a washboard than a thoroughfare because of shifting
ground. Building foundations in Bethel move and crack as well. Some
roads, airport runways and parking areas have to be reinforced with
liquid-filled pipes that transfer heat out of the permafrost to keep the
ground from slumping.
The thawing of permafrost is a gradual
process. Ground is fully frozen in winter, and begins to thaw from the
top down as air temperatures rise in spring. As average temperatures
increase over years, this thawed, or active, layer can increase in
depth.
At the field station, the researchers are
especially interested in how wildfires affect the permafrost. Because
burning removes some of the vegetation that acts as insulation, the
theory is that burning should cause permafrost to thaw more.
In the field, Sarah Ludwig, a Woods Hole research assistant (left),
and a student, Laura Jardine, extract a core of permafrost. In the lab,
Ms. Jardine cuts the core with a saw. Stash Wislocki, except for last photo, by John Schade
Parts of the tundra here burned in the 1970s
and in the summer of 2015, so the researchers took cores from both
burned and unburned areas. Scientists wrestled with the bulky power
auger as its stainless steel tube worked its way into the hard
permafrost. Cores — often containing thin layers of solid ice — were
labeled, packed in a cooler and sent by helicopter to a freezer in
Bethel.
Thawing permafrost underneath or at the edge
of a lake can cause it to drain like a leaky bathtub. Thawing elsewhere
can bring about small elevation changes that can in turn lead to changes
in water flow through the landscape, drying out some parts of the
tundra and turning others into bogs.
Beyond the local effects on plant and animal
life, the landscape changes can have an important climate change impact,
by altering the mix of carbon dioxide and methane that is emitted.
Although methane does not persist in the atmosphere for as long as
carbon dioxide, it has a far greater heat-trapping ability and can
contribute to more rapid warming.
So the researchers devote much of their time to studying the flow of water and the carbon and nutrients it contains.
John Schade
“It’s one of the big questions to tackle –
what’s wet and dry now, and what will be wet and dry in the future,” Dr.
Natali said. If the decomposing permafrost is wet, there will be less
oxygen available to the microbes, so they will produce more methane. If
the permafrost is dry, the decomposition will lead to more carbon
dioxide.
Estimates vary on how much carbon is
currently released from thawing permafrost worldwide, but by one
calculation emissions over the rest of the century could average about
1.5 billion tons a year, or about the same as current annual emissions
from fossil-fuel burning in the United States.
Already, thawing permafrost and warmer
temperatures are being blamed for rising carbon emissions in the Alaskan
tundra, both here and farther north. In a study earlier this year, researchers found that bacterial decomposition of thawed permafrost, as well as carbon dioxide produced by living vegetation, continues later into the fall because freezing of the surface is delayed.
The rise in emissions has been so
significant, the researchers found, that Alaska may be shifting from a
sink, or storehouse, of carbon, to a net source.
Dr. Holmes said that shift was not surprising
given the climate trend, and he would expect that sub-Arctic parts of
Siberia, Canada and other areas with permafrost may be undergoing
similar changes.
“There’s a massive amount of carbon that’s in
the ground, that’s built up slowly over thousands and thousands of
years,” he said.
“It’s been in a freezer, and that freezer is now turning into a refrigerator.”
Correction August 23, 2017
An earlier version of this article referred incorrectly to an estimate of the amount of carbon released from thawing permafrost worldwide. It is 1.5 billion tons a year averaged over the remainder of the century, not 1.5 billions tons a year currently.
Note: Highlighted areas of maps show over 50% probability of permafrost within one meter of ground surface.
Source: Data from “Distribution of Near-Surface Permafrost in Alaska: Estimates of Present and Future Conditions” by Neal J. Pastick and others in Remote Sensing of Environment, October 2015.
Source: Data from “Distribution of Near-Surface Permafrost in Alaska: Estimates of Present and Future Conditions” by Neal J. Pastick and others in Remote Sensing of Environment, October 2015.
