Methane: a Menace Surfaces, by Katey Walter
Anthony, in Scientific American, 2009 Dec.
Touchdown on the gravel runway at Cherskii in remote northeastern
Siberia sent the steel toe of a rubber boot into my buttocks.
The shoe had sprung free from gear stuffed between me and
my three colleagues packed into a tiny prop plane. This was
the last leg of my research team's five-day journey from the
University of Alaska Fairbanks across Russia to the Northeast
Science Station in the land of a million lakes, which we were
revisiting as part of our ongoing efforts to monitor a stirring
giant that could greatly speed up global warming.
These expeditions help us to understand how much of the perennially
frozen ground, known as permafrost, in Siberia and across
the Arctic is thawing, or close to thawing, and how much methane
the process could generate. The question grips us--and many
scientists and policy makers--because methane is a potent
greenhouse gas, packing 25 times more heating power, molecule
for molecule, than carbon dioxide. If the permafrost thaws
rapidly because of global warming worldwide, the planet could
get hotmetHAne ter more quickly than most models now predict.
Our data, combined with complementary analyses by others,
are revealing troubling trends.
Leaving the Freezer Door Open
Changes in permafrost are so worrisome because the frozen
ground, which covers 20 percent of the earth's land surface,
stores roughly 950 billion tons of carbon in the top several
tens of meters. (More permafrost can extend downward hundreds
of meters.) This carbon, in the form of dead plant and animal
remains, has accumulated over tens of thousands of years.
As long as it stays frozen beneath and between the many lakes,
it is safely sequestered from the air.
But when permafrost thaws, the carbon previously locked away
is made available to microbes, which rapidly degrade it, producing
gases. The same process happens if a freezer door is left
open; given long enough, food thaws and begins to rot. Oxygen
stimulates bacteria and fungi to aerobically decompose organic
matter, producing carbon dioxide. But oxygen is depleted in
soil that is waterlogged, such as in lake-bottom sediments;
in these conditions, anaerobic decomposition occurs, which
releases methane (in addition to some carbon dioxide). Under
lakes, the methane gas molecules form bubbles that escape
up through the water column, burst at the surface and enter
Anaerobic decomposition is the primary source of methane in
the Arctic. permafrost causes the ground surface to subside.
Runoff water readily fills the depressions, creating many
small, newly formed lakes, which begin to spew vast quantities
of methane as the permafrost that now lines their bottom thaws
much more extensively. Scars left behind reveal that this
process has been going on for the past 10,000 years, since
the earth entered the most recent interglacial warm period.
Satellite recordings made during recent decades suggest, however,
that permafrost thaw may be accelerating.
Those recordings are consistent with observations made at
numerous field-monitoring sites across Alaska and Siberia
maintained by my Fairbanks colleague Vladimir E. Romanovsky
and others. Romanovsky notes that permafrost temperature at
the sites has been rising since the early 1970s. Based on
those measurements, he calculates that one third to one half
of permafrost in Alaska is now within one degree to one and
a half degrees Celsius of thawing; in some places worldwide,
it is already crossing that critical zero degrees C threshold.
Ongoing observations, made by my research team during trips
to Cherskii and numerous other sites and by our colleagues,
reinforce the sense that thawing is accelerating and indicate
that the emissions could be much greater than anticipated.
My group's latest estimates are that under current warming
rates, by 2100 permafrost thawing could boost methane emissions
far beyond what would be produced by all other natural and
man-made sources. The added greenhouse gas, along with the
extra carbon dioxide that exposed, thawing ground would release,
together could raise the mean annual temperature of the earth
by an additional 0.32 degree C, according to Vladimir Alexeev,
also at Fairbanks.
That increase may sound minor, but it is not; it would contribute
significantly to globalwarming-induced upset of weather patterns,
sea level, agriculture and disease dispersal. If deeper sources
of methane were to escape--such as that stored in material
known as methane hydrates--the temperature rise could be as
high as several degrees. Therefore, humankind has more reason
than ever to aggressively slow the current rate of warming
so that we do not push large regions of the Arctic over the
threshold. Vast swaths of permafrost will thaw by 2050 and
2100 if global warming continues unabated, releasing large
quantities of methane that will worsen warming.
The Mother Lode in Siberia
Probing regions such as Cherskii is key to verifying --or
revising--our estimations. Walking along a Siberian riverbank
with my colleague from the Northeast Science Station, Sergei
A. Zimov, I am careful where I stop. The skin of the earth
is only a half meter thick, made up largely of muddy, mossy
peat that sits loosely atop ice that is 40 to 80 meters deep.
The stunted trees are slanted at various angles in this "drunken
forest" because they cannot send roots into the frozen
ground, and cycles of summer thaws generate large heaves.
Behind me, one drunken tree crashes to the ground; through
the torn blanket of forest floor we see the shiny black surface
of solid ice and catch the musty scent of decomposing organic
matter. It is also hard not to stub one's toe on the plethora
of scattered bones: woolly rhinoceros, mammoth, Pleistocene
lion, bear and horse.
To Zimov, this region is a goldmine--and not because of the
tusks and skulls of extinct fauna. In 1989, spurred by an
interest in the amount of carbon locked in the ground, he
led a group of young scientists that set up the isolated Northeast
Science Station to monitor permafrost in tundra and taiga
year-round. The researchers traveled the great Russian rivers
in small skiffs and scaled cliffs of permafrost without ropes
to measure carbon content, the harbinger of methane release.
With army tanks and bulldozers, they simulated disturbances
that remove surface soil in the way that severe wildfires
do. Their experiments proved the size and importance of the
permafrost carbon pool to the world.
But why did Zimov--and my group later-- concentrate studies
here, in a region known previously only for its Soviet gulags?
Because not all permafrost is the same. Any ground where the
mean annual temperature is below zero degrees C for at least
two consecutive years is classified as permafrost, whether
ice is present or not. This vast part of Siberia contains
a distinct type of permafrost called yedoma, rich in ice and
carbon --both central to the methane story. Massive wedges
of ice 10 to 80 meters high and smaller lenses constitute
up to 90 percent of the ground volume; the remainder is columns
of organicrich soil, a cornucopia of the remains of Pleistocene
mammals and the grasses they once ate.
Yedoma formed over roughly 1.8 million square kilometers in
Siberia and in a few pockets of North America during the end
of the last Ice Age. The organic matter froze in place before
microbes could decompose it. A huge storehouse of food was
being locked away until conditions would change, leaving the
freezer door open.
A warmer climate recently has helped melt the yedoma ice,
creating lakes. Vegetation collapses into the edges as the
ground thaws and subsides, a process known as thermokarst.
Today lakes cover up to 30 percent of Siberia. Further melting
makes them larger and deeper, coalescing into broad methane-producing
Blown Away by Bubbles
During the 1990s researchers at the Northeast Science Station
observed that methane was bubbling out of the bottoms of lakes
year-round but they did not know how important the lakes might
be globally. Hence, my rough landing by plane in Cherskii
this past August, for my ninth expedition of wading into voraciously
expanding thermokarst lakes, to measure changes in permafrost
and the release of methane.
My quest had begun as a Ph.D. research project in 2000. At
the time, scientists knew that levels of methane--the third
most abundant greenhouse gas in the atmosphere after carbon
dioxide and water vapor--were rising. The amount and the rate
of increased emissions were unprecedented during the previous
650,000 years. Evidence indicated that in bygone eras the
methane concentration in the atmosphere fluctuated by 50 percent
in association with natural climate variations over thousands
of years. But that change was slim by comparison with the
nearly 160 percent increase that had occurred since the mid-1700s,
rising from 700 parts per billion (ppb) before the industrial
revolution to almost 1,800 ppb when I started my project.
Scientists also knew that agriculture, industry, landfills
and other human activities were clearly involved in the recent
rise, yet roughly half of the methane entering the atmosphere
every year was coming from natural sources. No one, however,
had determined what the bulk of those sources were.
From 2001 to 2004 I split my time between my cabin in Fairbanks
and working with Zimov and others in Cherskii, living with
the few local Russian families. In the attic library above
our little, yellow wooden research station I spent long nights
cobbling together plastic floats that I could place on the
lakes to capture bubbles of methane. I dropped the traps by
leaning over the side of abandoned boats that I claimed, and
I checked them daily to record the volume of gas collected
under their large jellyfishlike skirts. In the beginning I
did not capture much methane.
Winter comes early, and one October morning when the black
ice was barely thick enough to support my weight I walked
out onto the shiny surface and exclaimed, "Aha!"
It was as if I was looking at the night sky. Brilliant clusters
of white bubbles were trapped in the thin black ice, scattered
across the surface, in effect showing me a map of the bubbling
point sources, or seeps, in the lake bed below. I stabbed
an iron spear into one big white pocket and a wind rushed
upward. I struck a match, which ignited a flame that shot
up five meters high, knocking me backward, burning my face
and singeing my eyebrows. Methane!
All winter I ventured across frozen lakes to set more traps
above these seeps. More than once I stepped unknowingly on
a bubbling hotspot and plunged into ice-cold water. Methane
hotspots in lake beds can emit so much gas that the convection
caused by bubbling can prevent all but a thin skin of ice
from forming above, leaving brittle openings the size of manhole
covers even when the air temperature reaches -50 degrees C
in the dark Siberian winter. I caught as much as 25 liters
(eight gallons) of methane each day from individual seeps,
much more than scientists usually find. I kept maps of the
hotspots and tallies of their emissions across numerous lakes.
The strongest bubbling occurred near the margins of lakes
where permafrost was most actively thawing. The radiocarbon
age of the gas, up to 43,000 years old in some places, pointed
to yedoma carbon as the culprit.
From 2002 to 2009 I conducted methaneseep surveys on 60 lakes
of different types and sizes in Siberia and Alaska. What scientists
were not expecting was that the increase in methane emissions
across the study region was disproportional to the increase
in lake area over that same region. It was nearly 45 percent
greater. It was accelerating.
Extrapolated to lakes across the Arctic, my preliminary estimate
indicated that 14 million to 35 million metric tons of methane
a year were being released. Evidence from polar ice-core records
and radiocarbon dating of ancient drained lake basins has
revealed that 10,000 to 11,000 years ago thermokarst lakes
contributed substantially to abrupt climate warming--up to
87 percent of the Northern Hemisphere methane that helped
to end the Ice Age. This outpouring tells us that under the
right conditions, permafrost thaw and methane release can
pick up speed, creating a positive feedback loop: Pleistocene-age
carbon is released as methane, contributing to atmospheric
warming, which triggers more thawing and more methane release.
Now man-made warming threatens to once again trigger large
How fast might these feedbacks occur? In 2007 global climate
models reported by the Intergov ernmental Panel on Climate
Change (IPCC) projected the strongest future warming in the
high latitudes, with some models predicting a rise of seven
to eight degrees C by the end of the 21st century. Based on
numerous analyses, my colleagues and I predict that at least
50 billion tons of methane will escape from ther mo karst
lakes in Siberia as yedoma thaws during the next decades to
centuries. This amount is 10 times all the methane currently
in the atmosphere.
Fine-tuning the Models
Even with our best efforts, our current estimates beg more
sophisticated modeling as well as consideration of potential
negative feedbacks, which could serve as breaks on the system.
For instance, in Alaska, a record number of thermokarst lakes
are draining. Lakes formed in upland areas grow until they
hit a slope. Then the water flows downhill, causing erosion
and further drainage, sending melted sediment into rivers
and eventually the ocean. Drained basins fill in with new
vegetation, often becoming wetlands. Although they produce
methane when they are unfrozen in summer, their total annual
emissions are often less than those of lakes.
It is hard to say whether such potential processes would lessen
methane release by a sizable amount or just a few percentage
points. Two projects of mine, with my Fairbanks colleague
Guido Grosse, Lawrence Plug of Dalhousie University in Nova
Scotia, Mary Edwards of the University of Southampton in England
and others, began in 2008 to improve the first-order approximations
of positive and negative feedbacks. A key step is to produce
maps and a classification of thermokarst lakes and carbon
cycling for regions of Siberia and Alaska, which we hope to
draft by early 2010. The cross-disciplinary research links
ecological and emissions measurements, geophysics, remote
sensing, laboratory incubation of thawed permafrost soils
and lake sediments, and other disciplines. The goal is to
inform a quantitative model of methane and carbon dioxide
emissions from thermokarst lakes from the Last Glacial Maximum
(21,000 years ago) to the present and to forecast climate-warming
feedbacks of methane from lakes for the upcoming decades to
To help predict how future warming could affect thermokarst
lakes, Plug and a postdoctoral student working with us, Mark
Kessler, are developing two computer models. The first, a
single-lake model, will simulate the dynamics of a lake basin.
The second, a landscape model, includes hill-slope processes,
surface-water movement and landscape-scale permafrost changes.
The models will first be validated by comparison with landscapes
we are already studying, then against data from sediment cores
going back 15,000 years in Siberia and Alaska, and then against
other climate simulations from 21,000 years ago. The final
step will be to couple the thermokarst-lake models with the
vast Hadley Center Coupled Model that describes the circulation
of oceans and atmosphere--one of the major models used in
IPCC assessment reports. The result, we hope, will be a master
program that can fully model the extent and effects of permafrost
thaw, allowing us to calculate a future rate of methane release
and assess how that would drive global temperatures.
More fieldwork, of course, will continue to refine the data
going into such models. In 2010, with the help of a hovercraft,
we will investigate lakes along nearly 1,000 miles of Siberian
rivers and Arctic coast. A huge expedition will also retrieve
sediment cores from lakes dating back millennia. Field data,
together with remote sensing, will ultimately be used in the
Hadley Center program to model climate change drivers from
the Last Glacial Maximum to 200 years into the future. Maps
of predicted permafrost thaw and methane release should be
complete by April 2011.
If, as all indicators suggest, Arctic methane emissions from
permafrost are accelerating, a key question becomes: Can anything
be done to prevent methane release? One response would be
to extract the gas as a relatively clean fuel before it escapes.
But harvesting methane from the millions of lakes scattered
across vast regions is not economically viable, because the
seeps are too diffuse. Small communities that are close to
strong seeps might tap the methane as an energy source, however.
Zimov and his son, Nikita, have devised an intriguing plan
to help keep the permafrost in Siberia frozen. They are creating
a grassland ecosystem maintained by large northern herbivores
similar to those that existed in Siberia more than 10,000
years ago. They have introduced horses, moose, bears and wolves
to "Pleistocene Park," a 160-square-kilometer scientific
reserve in northeastern Siberia. They intend to bring back
musk ox and bison, depending on funding, which comes from
independent sources, the Russian government and U.S. agencies.
These grazing animals, along with mammoths, maintained a steppe-grassland
ecosystem years ago. The bright grassland biome is much more
efficient in reflecting incoming solar radiation than the
dark boreal forest that has currently replaced it, helping
to keep the underlying permafrost frozen. Furthermore, in
winter the grazers trample and excavate the snowpack to forage,
which allows the bitter cold to more readily chill the permafrost.
One man and his family have taken on a mammoth effort to save
the world from climate change by building Pleistocene Park.
Yet a global response is needed, in which every person, organization
and nation takes responsibility to reduce their carbon footprint.
Slowing emissions of carbon dioxide is the only way humankind
can avoid amplifying the feedback loop of greater warming
causing more permafrost thaw, which causes further warming.
We predict that if carbon emissions increase at their current
projected rate, northern lakes will release 100 million to
200 million tons of methane a year by 2100, much more than
the 14 million to 35 million tons they emit annually today.
Total emissions from all sources worldwide is about 550 million
tons a year, so permafrost thaw, if it remains unchecked,
would add another 20 to 40 percent, driving the additional
0.32 degree C rise in the earth's mean annual temperature
noted earlier. The world can ill afford to make climate change
that much worse. To reduce atmospheric carbon dioxide and
thereby slow permafrost thaw, we all must confront the elephant
in the room: people burning fossil fuels.