By Justin Gillis, The New York Times, December 16, 2011
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| Katey M. Walter Anthony, a scientist, investigated a plume of methane, a greenhouse gas, at an Alaskan lake. Dr. Walter Anthony is a leading researcher in studying the escape of methane (Photo: Josh Haner, NYT) |
FAIRBANKS, Alaska —
A bubble rose through a hole in the surface of a frozen lake. It popped,
followed by another, and another, as if a pot were somehow boiling in the icy
depths.
Every bursting
bubble sent up a puff of methane, a powerful greenhouse gas generated beneath
the lake from the decay of plant debris. These plants last saw the light of day
30,000 years ago and have been locked in a deep freeze — until now.
“That’s a hot
spot,” declared Katey M. Walter Anthony, a leading scientist in studying the
escape of methane. A few minutes later, she leaned perilously over the edge of
the ice, plunging a bottle into the water to grab a gas sample.
It was another
small clue for scientists struggling to understand one of the biggest looming
mysteries about the future of the earth.
Experts have long
known that northern lands were a storehouse of frozen carbon, locked up in the
form of leaves, roots and other organic matter trapped in icy soil — a mix
that, when thawed, can produce methane and carbon dioxide, gases that trap heat
and warm the planet. But they have been stunned in recent years to realize just
how much organic debris is there.
A recent estimate
suggests that the perennially frozen ground known as permafrost, which
underlies nearly a quarter of the Northern Hemisphere, contains twice as much
carbon as the entire atmosphere.
Temperatures are
warming across much of that region, primarily, scientists believe, because of
the rapid human release of greenhouse gases. Permafrost is warming, too. Some
has already thawed, and other signs are emerging that the frozen carbon may be
becoming unstable.
“It’s like broccoli
in your freezer,” said Kevin Schaefer, a scientist at the National Snow and Ice Data
Center in Boulder, Colo. “As long as the broccoli stays in the
freezer, it’s going to be O.K. But once you take it out of the freezer and put
it in the fridge, it will thaw out and eventually decay.”
If a substantial
amount of the carbon should enter the atmosphere, it would intensify the
planetary warming. An especially worrisome possibility is that a significant
proportion will emerge not as carbon dioxide, the gas that usually forms when
organic material breaks down, but as methane, produced when the breakdown
occurs in lakes or wetlands. Methane is especially potent at trapping the sun’s
heat, and the potential for large new methane emissions in the Arctic is one of
the biggest wild cards in climate science.
Scientists have
declared that understanding the problem is a major priority. The United States
Department of Energy and the European Union recently committed to new projects
aimed at doing so, and NASA is considering a similar plan. But researchers say
the money and people devoted to the issue are still minimal compared with the
risk.
For now, scientists
have many more questions than answers. Preliminary computer analyses, made only
recently, suggest that the Arctic and sub-Arctic regions could eventually
become an annual source of carbon equal to 15 percent or so of today’s yearly
emissions from human activities.
But those
calculations were deliberately cautious. A recent survey drew on the expertise of 41
permafrost scientists to offer more informal projections. They estimated that
if human fossil-fuel burning remained high and the planet warmed sharply, the
gases from permafrost could eventually equal 35 percent of today’s annual human
emissions.
The experts also
said that if humanity began getting its own emissions under control soon, the
greenhouse gases emerging from permafrost could be kept to a much lower level,
perhaps equivalent to 10 percent of today’s human emissions.
Even at the low
end, these numbers mean that the long-running international negotiations over
greenhouse gases are likely to become more difficult, with less room for
countries to continue burning large amounts of fossil fuels.
In the minds of
most experts, the chief worry is not that the carbon in the permafrost will
break down quickly — typical estimates say that will take more than a century,
perhaps several — but that once the decomposition starts, it will be impossible
to stop.
“Even if it’s 5 or
10 percent of today’s emissions, it’s exceptionally worrying, and 30 percent is
humongous,” said Josep G. Canadell, a scientist in Australia who runs a global
program to monitor greenhouse gases. “It will be a chronic source of emissions
that will last hundreds of years.”
A troubling trend
has emerged recently: Wildfires are increasing across much of the north, and
early research suggests that extensive burning could lead to a more rapid thaw
of permafrost.
Rise and Fall of
Permafrost
Standing on a bluff
the other day, overlooking an immense river valley, A. David McGuire, a
scientist from the University of Alaska, Fairbanks, sketched out two million
years of the region’s history. It was the peculiar geology of western North
America and eastern Siberia, he said, that caused so much plant debris to get
locked in an ice box there.
These areas were
not covered in glaciers during the last ice age, but the climate was frigid,
with powerful winds. The winds and rivers carried immense volumes of silt and
dust that settled in the lowlands of Alaska and Siberia.
A thin layer of
this soil thawed on top during the summers and grasses grew, capturing carbon
dioxide. In the bitter winters, grass roots, leaves and even animal parts froze
before they could decompose. Layer after layer of permafrost built up.
At the peak of the
ice age, 20,000 years ago, the frozen ground was more extensive than today,
stretching deep into parts of the lower 48 states that were not covered by ice
sheets. Climate-change contrarians like to point to that history, contending
that any melting of permafrost and ice sheets today is simply the tail end of
the ice age.
Citing permafrost
temperatures for northern Alaska — which, though rising rapidly, remain well
below freezing — an organization called the Center for the Study of Carbon
Dioxide and Global Change claimed that permafrost is in “no more danger of
being wiped out any time soon than it was in the days of our
great-grandparents.”
But mainstream
scientists, while hoping the breakdown of permafrost will indeed be slow,
reject that argument. They say the climate was reasonably stable for the past
10,000 years or so, during the period when human civilization arose. Now, as
people burn immense amounts of carbon in the form of fossil fuels, the planet’s
temperature is rising, and the Arctic is warming twice as fast. That,
scientists say, puts the remaining permafrost deposits at risk.
For several
decades, researchers have been monitoring permafrost temperatures in hundreds
of boreholes across the north. The temperatures have occasionally decreased in
some regions for periods as long as a decade, but the overall trend has been a relentlesss
rise, with temperatures now increasing fastest in the most northerly areas.
Thawing has been
most notable at the southern margins. Across huge areas, including much of
central Alaska, permafrost is hovering just below the freezing point, and is
expected to start thawing in earnest as soon as the 2020s. In northern Alaska
and northern Siberia, where permafrost is at least 12 degrees Fahrenheit below
freezing, experts say it should take longer.
“Even in a
greenhouse-warmed world, it will still get cold and dark in the Arctic in the
winter,” said Mark Serreze, director of the snow and ice data center in
Boulder.
Scientists need
better inventories of the ancient carbon. The best estimate so far was published in 2009 by
a Canadian scientist, Charles Tarnocai, and some colleagues. They calculated
that there was about 1.7 trillion tons of carbon in soils of the northern
regions, about 88 percent of it locked in permafrost. That is about two and a
half times the amount of carbon in the atmosphere.
Philippe Ciais, a
leading French scientist, wrote at the time that he was “stunned” by the
estimate, a large upward revision from previous calculations.
“If, in a warmer
world, bacteria decompose organic soil matter faster, releasing carbon
dioxide,” Dr. Ciais wrote, “this will set up a positive feedback loop, speeding
up global warming.”
Plumes of Methane
Katey
Walter Anthony had been told to hunt for methane, and she could not find it.
As a young
researcher at the University of Alaska, Fairbanks, she wanted to figure out how
much of that gas was escaping from lakes in areas of permafrost thaw. She was
doing field work in Siberia in 2000, scattering bubble traps around various
lakes in the summer, but she got almost nothing.
Then, that October,
the lakes froze over. Plumes of methane that had been hard to spot on a choppy
lake surface in summer suddenly became more visible.
“I went out on the
ice, this black ice, and it looked like the starry night sky,” Dr. Walter
Anthony said. “You could see these bubble clusters everywhere. I realized —
‘aha!’ — this is where all the methane is.”
When organic
material comes out of the deep freeze, it is consumed by bacteria. If the
material is well-aerated, bacteria that breathe oxygen will perform the
breakdown, and the carbon will enter the air as carbon dioxide, the primary
greenhouse gas. But in areas where oxygen is limited, like the bottom of a lake
or wetland, a group of bacteria called methanogens will break down the organic
material, and the carbon will emerge as methane.
Scientists are
worried about both gases. They believe that most of the carbon will emerge as
carbon dioxide, with only a few percent of it being converted to methane. But
because methane is such a potent greenhouse gas, the 41 experts in the recent
survey predicted that it would trap about as much heat as the carbon dioxide
would.
Dr. Walter
Anthony’s seminal discovery was that methane rose from lake bottoms not as
diffuse leaks, as many scientists had long assumed, but in a handful of
scattered, vigorous plumes, some of them capable of putting out many quarts of
gas per day. In certain lakes they accounted for most of the emerging methane,
but previous research had not taken them into consideration. That meant big upward
revisions were probably needed in estimates of the amount of methane lakes
might emit as permafrost thawed.
Most of the lakes
Dr. Walter Anthony studies were formed by a peculiar mechanism. Permafrost that
is frozen hard supports the ground surface, almost the way a concrete pillar
supports a building. But when thaw begins, the ground sometimes turns to mush
and the entire land surface collapses into a low-lying area, known as a
thermokarst. A lake or wetland can form there, with the dark surface of the
water capturing the sun’s heat and causing still more permafrost to thaw
nearby.
Near thermokarst
locations, trees often lean crazily because their roots are disturbed by the
rapid changes in the underlying landscape, creating “drunken forests.” And the
thawing, as it feeds on itself, frees up more and more ancient plant debris.
One recent day, in
11-degree weather, Dr. Walter Anthony and an assistant, Amy Strohm, dragged
equipment onto two frozen thermokarst lakes near Fairbanks. The fall had been
unusually warm and the ice was thin, emitting thunderous cracks — but it held.
In spots, methane bubbled so vigorously it had prevented the water from
freezing. Dr. Walter Anthony, six months pregnant, bent over one plume to
retrieve samples.
“This is thinner
ice than we like,” she said. “Don’t tell my mother-in-law! My own mother
doesn’t know.”
Dr. Walter Anthony
had already run chemical tests on the methane from one of the lakes, dating the
carbon molecules within the gas to 30,000 years ago. She has found carbon that
old emerging at numerous spots around Fairbanks, and carbon as old as 43,000
years emerging from lakes in Siberia.
“These grasses were
food for mammoths during the end of the last ice age,” Dr. Walter Anthony said.
“It was in the freezer for 30,000 to 40,000 years, and now the freezer door is
open.”
Scientists are not
sure yet whether thermokarst lakes will become more common throughout the
Arctic in a warming climate, a development that could greatly accelerate
permafrost thaw and methane production. But they have already started to see
increases in some regions, including northernmost Alaska.
“We expect
increased thermokarst activity could be a very strong effect, but we don’t
really know,” said Guido Grosse, another scientist at the University of Alaska,
Fairbanks. He is working with Dr. Walter Anthony on precision mapping of
thermokarst lakes and methane seeps, in the hope that the team can ultimately
use satellites and aerial photography to detect trends.
With this kind of
work still in the early stages, researchers are worried that the changes in the
region may already be outrunning their ability to understand them, or to
predict what will happen.
When the Tundra
Burns
One day in 2007, on
the plain in northern Alaska, a lightning strike set the tundra on fire.
Historically,
tundra, a landscape of lichens, mosses and delicate plants, was too damp to
burn. But the climate in the area is warming and drying, and fires in both the
tundra and forest regions of Alaska are increasing.
The Anaktuvuk River
fire burned about 400 square miles of tundra, and work on lake sediments showed
that no fire of that scale had occurred in the region in at
least 5,000 years.
Scientists have
calculated that the fire and its aftermath sent a huge pulse of carbon into the
air — as much as would be emitted in two years by a city the size of Miami.
Scientists say the fire thawed the upper layer of permafrost and set off what
they fear will be permanent shifts in the landscape.
Up to now, the
Arctic has been absorbing carbon, on balance, and was once expected to keep
doing so throughout this century. But recent analyses suggest that the
permafrost thaw could turn the Arctic into a net source of carbon, possibly
within a decade or two, and those studies did not account for fire.
“I maintain that
the fastest way you’re going to lose permafrost and release permafrost carbon
to the atmosphere is increasing fire frequency,” said Michelle C. Mack, a
University of Florida scientist who is studying the Anaktuvuk fire. “It’s a rapid and
catastrophic way you could completely change everything.”
The essential
question scientists need to answer is whether the many factors they do not yet
understand could speed the release of carbon from permafrost — or, possibly,
slow it more than they expect.
For instance,
nutrients released from thawing permafrost could spur denser plant growth in
the Arctic, and the plants would take up some carbon dioxide. Conversely,
should fires like the one at Anaktuvuk River race across warming northern
landscapes, immense amounts of organic material in vegetation, soils, peat
deposits and thawed permafrost could burn.
Edward A. G.
Schuur, a University of Florida researcher who has done extensive field work in
Alaska, is worried by the changes he already sees, including the discovery that
carbon buried since before the dawn of civilization is now escaping.
“To me, it’s a
spine-tingling feeling, if it’s really old carbon that hasn’t been in the air
for a long time, and now it’s entering the air,” Dr. Schuur said. “That’s the
fingerprint of a major disruption, and we aren’t going to be able to turn it
off someday.”
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