Recently discovered microbe is key player in climate change.
Study site, Stordalen Mire in Abisko National Park in Sweden, just north of the Arctic Circle. Credit: Scott Saleska
22
October, 2014
As
permafrost soils thaw under the influence of global warming,
communities of soil microbes act as potent amplifiers of global
climate change, an international study has shown.
Tiny soil
microbes are
among the world's biggest potential amplifiers of human-caused
climate change, but whether microbial communities are mere slaves to
their environment or influential actors in their own right is an open
question. Now, research by an international team of scientists from
the U.S., Sweden and Australia, led by University of Arizona
scientists, shows that a single species of microbe, discovered only
very recently, is an unexpected key player in climate change.
The
findings, published in the journal Nature,
should help scientists improve their simulations of future climate by
replacing assumptions about the different greenhouse
gases emitted
from thawing permafrost with new understanding of how different
communities of microbes control the release of these gases.
Earlier
this year, the international team discovered that a single species of
microbe, previously undescribed by science, was prominent in
permafrost soils in northern Sweden that have begun to thaw under the
effect of globally rising temperatures. Researchers suspected that it
played a significant role in global
warming by
liberating vast amounts of carbon stored in permafrost soil close to
the Arctic Circle in the form of methane, a powerful greenhouse gas
trapping heat in the Earth's atmosphere. But the actual role of this
microbe—assigned the preliminary name Methanoflorens
stordalenmirensis, which roughly translates to "methane-bloomer
from the Stordalen Mire"—was unknown.
The
new research nails down the role of the new microbe, finding that the
sheer abundance of Methanoflorens, as compared to other microbial
species in thawing permafrost, should help to predict their
collective impact on future climate
change.
"If
you think of the African savanna as an analogy, you could say that
both lions and elephants produce carbon dioxide, but they eat
different things," said senior author Scott Saleska, an
associate professor in the UA's Department of Ecology and
Evolutionary Biology and director of the UA's new Ecosystem Genomics
Institute. "In Methanoflorens, we discovered the microbial
equivalent of an elephant, an organism that plays an enormously
important role in what happens to the whole ecosystem."
Significantly,
the study revealed that because of these microbial activities, all
wetlands are not the same when it comes to methane release.
"The
models assume a certain ratio between different forms, or isotopes,
of the carbon in the methane molecules, and the actual recorded ratio
turns out to be different," said lead author Carmody McCalley, a
scientist at the Earth Systems Research Center at the University of
New Hampshire who conducted the study while she was a postdoctoral
researcher at UA. "This has been a major shortcoming of current
climate models. Because they assume the wrong isotope ratio coming
out of the wetlands, the models overestimate carbon released by
biological processes and underestimate carbon released by human
activities such as fossil-fuel burning."
Soil
microbes can make methane two different ways: either from acetate, an
organic molecule that comes from plants, or from carbon dioxide and
hydrogen.
"Both
processes produce energy for the microbe, and the microbe breathes
out methane like we breathe out carbon
dioxide,"
McCalley said. "But we find that in thawing permafrost, most
methane initially doesn't come from acetate as previously assumed,
but the other pathway. This ratio then shifts towards previous
estimates as the frozen soils are turned into wetlands and acetate
becomes the preferred carbon source."
One
of the big questions facing climate scientists, according to Saleska,
is how much of the carbon stored in soils is released into the
atmosphere by microbial activity.
"As
the 'global freezer' of permafrost is failing under the influence of
warming, we need to better understand how soil microbes
release carbon on
a larger, ecosystem-wide level and what is going to happen with it,"
he said.
Said
UA co-author Virginia Rich: "For years, there's been a debate
about whether microbial ecology 'matters' to what an ecosystem
collectively does—in this case, releasing greenhouse gases of
different forms—or whether microbes are just slaves to the system's
physics and chemistry. This work shows that microbial ecology matters
to a great degree, and that we need to pay more attention to the
types of microbes living in those thawing ecosystems."
Added
McCalley: "By taking microbial ecology into account, we can
accurately set up climate models to identify how much methane comes
from thawing permafrost versus other sources such as fossil-fuel
burning."
Explore
further: Methane-producing
microbe blooms in permafrost thaw
More
information: 'Methane
dynamics regulated by microbial community response to permafrost
thaw' Nature ,
23 October 2014. DOI:
10.1038/nature13798
More information: 'Methane dynamics regulated by microbial community response to permafrost thaw' Nature , 23 October 2014. DOI: 10.1038/nature13798
The Arctic Methane Monster’s Nasty Little Helpers: Study Finds Ancient, Methane Producing, Archaea Gorge on Tundra Melt.
12
March, 2014
An
emerging methane feedback in the Arctic. It’s something that, since
last summer, I’ve
been calling the Arctic Methane Monster. A
beast of a thing composed of giant reserves of sea bed methane and an
immense store of carbon locked away in Arctic tundra.
How
dangerous and vicious the monster ends up being to a world set to
rapidly warm by humans depends largely on three factors. First —
how fast methane is released from warming stores in the sea bed.
Second — how swiftly and to what degree the tundra carbon store is
released as methane. Third — how large the stores of carbon and
methane ultimately are.
(Thawing permafrost and organic carbon in Yedoma region of Russia. Image source: NASA.)
On
the issue of the first and third questions, scientists are divided
between those like Peter Wadhams, Natalia Shakhova and Igor Simeletov
who believe that large methane pulses from a rapidly warming Arctic
Ocean are now possible and warrant serious consideration and those
like Gavin Schmidt and David Archer — both top scientists in their
own right — who believe the model assessments showing a much slower
release are at least some cause for comfort. Further complicating the
issue is that estimates of sea-bed methane stores range widely with
the East Siberian Arctic Shelf region alone asserted to contain
anywhere between 250 and 1500 gigatons of methane (See
Arctic Carbon Stores Assessment Here).
With
such wide-ranging estimations and observations, it’s no wonder that
a major scientific controversy has erupted over the issue of sea bed
methane release. This back and forth comes in the foreground of
observed large (but not catastrophic) sea-bed emissions and what
appears to be a growing Arctic methane release. A controversy that,
in itself, does little inspire confidence in a positive outcome.
But
on the second point, an issue that some are now calling the compost
bomb, most scientists are in agreement that the massive carbon store
locked in the swiftly thawing tundra is a matter of serious and
immediate concern.
Tundra
Thaw by Human GHG Now Practically Inevitable
At
issue here is the initial power of the human heat forcing and what
consequences that forcing is likely to unlock. Consequences that are
directly tied to the amount of greenhouse gasses we emit. A
total forcing that is now likely equivalent to around 425 CO2e when
taking into account the effect of human aerosols and an even more
ominous 480 CO2e when and if those aerosols fall out (IPCC
and MIT).
The
first number, 425 CO2e, were it to remain stable over years, decades
and centuries, is
enough push global temperatures above the 1.5 C warming threshold
that would thaw the northern hemisphere tundra. And within this
tundra is
locked a store of about 1,500 gigatons of carbon. A massive store
that is set to eventually, thaw, decompose and release its carbon as
either CO2 or methane over the long period of warmth that is to come.
(Northern Hemisphere Permafrost Zones. Image source: NASA.)
The
immense size of this carbon store represents an extreme risk both for
extending the period of human warming and for, potentially,
generating a feedback in which natural warming adds to, rather than
simply extends, human warming. By comparison, human fossil fuel
emissions have already resulted in about 540 gigatons of carbon being
released into the atmosphere. The tundra store alone represents
nearly three times this amount. But the concern is not just the
massive size of the tundra store now set to thaw, or the rate at
which the tundra will, eventually, release its carbon to the
atmosphere. The concern is also how much of the tundra store carbon
is released as either methane or CO2.
Methane
Provides a Strong Amplifying Feedback
Since
methane’s radiative
absorption is about 35 times that of CO2 by volume in the IPCC
climate assessments (and its short term global warming
potential is as much as 72 to 105 times that of a comparable
amount of CO2) and since methane release sets off other
feedbacks by turning into CO2 after it is oxidized and by increasing
atmospheric water vapor, a strong greenhouse agent in its own right,
a significant portion of tundra carbon being liberated as methane
could result in a rather powerful heat amplification. In the worst
case, such an amplification could set off conditions similar to those
during which other mini-greenhouse gas runaways occurred — such as
the Permian, Triassic and PETM events.
Which
is why the release of a new paper should be cause for serious
concern.
Ancient
Archaea — The Arctic Methane Monster’s Nasty Little Helpers
This
week, a paper published in Nature
Communications described
findings based on a study of thawing Swedish permafrost. The study
investigated how microbes responded to thawing tundra in various
mires throughout warming sections of Sweden. What they discovered was
the increased prevalence of an ancient methane producing
micro-organism.
Billions
of years ago, methane producing cyanobacteria or archaea were
prevalent in the world’s oceans. The methane they produced helped
keep the Earth warm at a time when solar output was much less than it
is today. Later, as oxygen producing plants emerged, the archaea, to
which oxygen was a poison, retreated into the anoxic corners of the
more modern world. Today, they live in the dark, in the mud, or in
the depths of oceans. There, they continue to eek out an existence by
turning hydrogen and carbon dioxide into methane.
A
kind of archaea, the newly discovered organism, named methanoflorens
stordalenmirensis,
was found to be exploding through sections of rapidly melting Swedish
tundra. In fact, it is so at home in regions of melting permafrost
that it blooms in the same way algae blooms in the ocean. As a
result, it comes to dominate the microbial environment, representing
90% of the methanogens and crowding out many of the other microbes.
(Methanogen shows global distribution. Each dot indicates a location wheremethanoflorens stordalenmirensis was discovered. Image source: Nature.)
That
these massive archaea blooms can effectively convert large portions
of the newly liberated tundra carbon store into methane was not at
all lost on researchers:
“Methanoflorens
stordalenmirensis seems to be a indicator species for melting
permafrost. It is rarely found where there is permafrost, but
where the peat is warmer and the permafrost is melting we can see
that it just grows and grows.
It is possible that we can use it to measure the health of mires and
their permafrost. The recently documented
global distribution also shows, on a much larger scale, that this
microbe spreads to new permafrost areas in time with them thawing
out. This is not good news for a stable climate“,
said study author Rhiannon Mondav.
So
what we have here is a billions year old microbe that thrives in wet
regions called mires where permafrost is melting, rapidly converts
tundra carbon to methane, readily spreads to new zones where
permafrost melt occurs, and explodes into algae like blooms to
dominate these environment.
One
could not ask for a set of more diabolic little helpers for the
already very disturbing Arctic Methane Monster…
Implications
Going Forward: Arctic Methane Emission Not Currently Catastrophic,
But Likely to Continue to Grow
Recent
research shows that the current methane emission from all natural
sources north of 53 degrees north latitude is on the order of 81
trillion grams (TG) each year. A portion of this, about 17 TG, comes
from the East Siberian Arctic Shelf. Other inputs are from sea bed
sources, thawing tundra and existing wetlands in the region.
Meanwhile, the global emission, including both human and natural
sources is in the range of about 600 TG each year. Overall, this
emission is enough to overwhelm current sinks by about 40 TG each
year, which results in continuing increases of atmospheric methane.
(Atmospheric methane levels since 1969, Mauna Loa, show levels rising by about 200 ppb over the 45 year period. Image source: NOAA ESRL.)
As
more and more of the tundra melts and as seabed methane continues to
warm it is likely that total Arctic methane emissions will continue
to rise, perhaps eventually rivaling or, in the worst case, exceeding
the size of the human methane emission (350 TG). But, to do so,
current Arctic and boreal emissions would have to more than quadruple
— either through a slow increase (high likelihood) or through more
catastrophic large pulse events (lower likelihood, but still enough
for serious concern). By contrast, recent warm years have shown
increases in the rate of methane flux/emission of around 5% with the
average flux increase being around 2%.
It
is worth noting that NOAA and a number of other agencies do track
methane emissions in the Arctic but that a comprehensive tool set for
accurately tracking the total emission does not appear to be
currently available. Instead, various studies are conducted in an
effort to capture total emissions levels. Monitoring does, however,
track total atmospheric values.
Links:
No comments:
Post a Comment
Note: only a member of this blog may post a comment.