Methane Bomb Squad Part 4: Dr. Richard Alley and the National Academy

October 17, 2014

Along with Dr. Jim Byrne, and Geoff Haines Stiles, I interviewed Dr. Richard Alley, along with 22 other leading scientists at last year’s American Geophysical Union Fall Meeting.

Dr. Alley had just finished work as part of a National Academy of Science project on Abrupt Impacts of Climate Change – a useful and authoritative look at potential unforeseen and sudden impacts, including the possible release of methane from ocean shelves.  Below is most of the section on that issue, and Dr. Alley gives a 5 minute non-technical synopsis above.
Takeaway, potential problem, most likely on century or milennial time scales, but can’t rule out surprises.

My goal in this series is to make available some of the key documents on this issue, so that, first of all, I get the chance to evaluate them myself – but also for other folks to be able to follow the threads. There will be more this weekend.
Below, the section of the report mentioned above, dealing with undersea methane.

National Academy of Science – Abrupt Impacts of Climate Change – Anticipating Surprises (free download)

Potential response to a warming climate Climate change has the potential to impact
ocean methane hydrate deposits through changes in ocean water temperature near
the sea bed, or variations in pressure associated with changing sea level. Of the two,
temperature changes are thought to be most important, both during the last deglaciation
(Mienert et al., 2005) and also in the future. Warming bottom waters in deeper
parts of the ocean, where surface sediment is much colder than freezing and the hydrate
stability zone is relatively thick, would not thaw hydrates near the sediment surface,
but downward heat diffusion into the sediment column would thin the stability
zone from below, causing basal hydrates to decompose, releasing gaseous methane.

The time scale for this mechanism of hydrate thawing is on the order of centuries to
millennia, limited by the rate of anthropogenic heat diffusion into the deep ocean and
sediment column. Even on the Siberian continental margin, where water temperatures
are colder than the global average, and where the sediment column retains the cold
imprint from its exposure to the atmosphere during the last glacial time 20,000 years
ago, any methane hydrate must be buried under at least 200 m of water or sediment.
Bottom waters at depths of 50 or 100 m might warm relatively quickly with a collapse
in sea ice cover, but it would take centuries for that heat to diffuse through the 100-
150 m of sediment column to the hydrate stability zone. Thus the release of 50 Gt C
from the Siberian continental shelf in 10 years as postulated by Whiteman et al. (2013)
is unlikely.
The proportion of this gas production that will reach the atmosphere as CH4 is likely
to be small. To reach the atmosphere, the CH4 would have to avoid oxidization within
the sediment column (a chemical trap) and re-freezing within the stability zone shallower
in the sediment column (a cold trap). However, the hydrate stability zone thickness
decreases to zero near the top of its depth range in the ocean, and an increase in
water column temperature there could eliminate the stability zone entirely, potentially
providing an easier pathway for methane to reach the sea floor. Episodic and explosive
escapes of gaseous methane from the sediment column have been documented by
kilometer-scale “wipeout zones” in seismic images (Riedel et al., 2002), and pockmarks
on the sea floor, called eruption craters (Hill et al., 2004). However, the processes responsible
for these observations are too poorly understood to predict what fraction of
deeper CH4 might be released through them.

Most of the methane gas that emerges from the sea floor dissolves in the water
column and oxidizes to CO2 instead of reaching the atmosphere. Bubble plumes tend
to dissolve on a height scale of tens of meters (Rehder et al., 2002; Kessler et al., 2011),
although larger plumes, consisting of larger bubbles, do rise farther. However, even in
the cold Arctic Ocean, methane hydrate is only stable below about 200 m water depth,
making for an inefficient pathway to the atmosphere at best. The highest oceanic
methane fluxes to the atmosphere in the Arctic are probably in the coastal zone, associated
with erosion of coastal permafrost (Shakhova et al., 2010b). In this region (and
also in terrestrial lakes) the methane flux to the atmosphere is strongly impacted by
ice formation on the water surface (Walter et al., 2007), providing another mechanism
for climate feedback (He et al., 2013).

Another, more abrupt way to transfer methane hydrate from the sediment column to
the atmosphere is by way of a submarine landslide. Methane hydrate floats in seawater
just as water ice floats, and it also has greater potential to reach the atmosphere
than methane bubbles (Brewer et al., 2002). The largest known submarine landslide
(called Storegga) occurred ~8000 years ago, as documented in sediment deposits off
Norway (Mienert et al., 2005). The volume of sliding material multiplied by a reasonable
hydrate fraction in the pore space yields a possible methane source of about
1 Gt C. The climatic impact of this quantity of methane would be comparable to that
of a volcanic eruption (although warming rather than cooling). As such it would have
a significant climate impact, but one that is likely to be smaller than that of the anthropogenic
CO2 rise (Archer, 2007).
Over time scales of centuries and millennia, the ocean hydrate pool has the potential
to be a significant amplifier of the anthropogenic fossil fuel carbon release. Because
the chemistry of the ocean equilibrates with that of the atmosphere (on time scales
of decades to centuries), methane oxidized to CO2 in the water column will eventually
increase the atmospheric CO2 burden (Archer and Buffett, 2005). As with decomposing
permafrost soils, such release of carbon from the ocean hydrate pool would represent
a change to the Earth’s climate system that is irreversible over centuries to millennia.

Modeling the response of ocean hydrates to climate change is in its infancy. The largest
uncertainty is the concentration of methane hydrate, especially in the shallow sediment
column near the sediment water interface. Coupled atmosphere-ocean climate
models can be used to simulate the thermal response of the ocean water column to
climate change with a moderate degree of uncertainty and the subsequent penetration
of heat into the sediment column. The response of an assumed column inventory
of hydrate to warming can be simulated (Lamarque, 2008; Reagan and Moridis, 2009;
Reagan et al., 2011), but the results depend strongly on the assumed hydrate concentrations.

Another approach is to “grow” the sediment column through geologic time
to obtain an initial condition for a climate change perturbation scenario (Archer et al.,
2012), but uncertainties in various model parameters, such as the methane production
rate and the fate of bubbles in the sediment column, prevent a well-constrained
model forecast of the methane hydrate response to climate warming.
In summary, the ocean methane hydrate pool has strong potential to amplify the human
CO2 release from fossil fuel combustion over times scales of decades to centuries.
While anthropogenic warming should accelerate the thawing of offshore permafrost
via warming of Arctic Ocean shelf waters, this impact should be considered additive to
a broader thawing trend that has been underway for thousands of years.

10 Responses to “Methane Bomb Squad Part 4: Dr. Richard Alley and the National Academy”

  1. Susan Hatch Says:

    Will you also interview Shakhova?

  2. redskylite Says:

    Barrow, Alaska, U.S.A, a place where atmospheric GHG’s and temperatures are monitored scientifically by NOAA, and where temperatures have risen by more than an astonishing and alarming +7 °C over a climatic period of 3 decades.

    I am sure methane has played a significant part of that abrupt and frightening change. I am angry and frustrated and do not want to hear from any more lame deniers, who turn their back on decent, educated and savvy people like Dr Alley.

    Do we listen to the international body of scientists who tell us to keep atmospheric CO2 below 450 ppm ? Or do we think we know better. ?

    • redskylite Says:

      Many thanks for the link to the excellent “Anticipating Surprises” report, I need to lock myself into a quiet room for a few hours to fully digest. I do note that the report calls for the creation of a “Abrupt Change Early Warning System”, which hopefully will be formed sometime soon.

      It is incredible that we have already locked in so many long term changes. The only one I am likely to see is the disappearance of Summer Arctic sea ice, which ironically may even increase man’s fossil fuelled endeavours.

      A truly sobering and amazing document.

  3. […] to the possibility of an abrupt methane release, I thought I might post this video that I found on Climate Denial Crock of the Week (I hope Peter Sinclair doesn’t mind me using it). It’s Richard Alley explaining that […]

  4. redskylite Says:

    I found this interesting National Geographic item on the National Research Council’s 2013 report and recommendation for an “Abrupt Change Early Warning System” to be created.

    No sign of the system actually being set up so far.

  5. […] it is not as serious as atmospheric CO2 i.e. if we cannot control that, we are f*ck anyway. Methane Bomb Squad Part 4: Dr. Richard Alley and the National Academy | Climate Denial Crock of the … Sign in or Register Now to […]

  6. How about giving some thought as to how that methane can be harvested?

    It is a valuable commodity and there would be monetary advantage in
    capturing it before it joins and further pollutes the atmosphere.

    If we generally know where it is bubbling up, how about capturing it
    in something like a plastic sheet on the surface of the water.

    This is a Very good time to try to think of ways to mitigate these problems
    instead of fighting with each other about who is to blame.

    • dumboldguy Says:

      A technocentric approach. Impractical and wishful thinking. The only kind of “mitigation” that makes sense is to alter the conditions that are causing it to bubble up in the first place.

      And who is “fighting with each other about who is to blame”? To trot out Pogo again, he famously said “We have met the enemy and he is us”. The entire human species is “to blame” in greater or lesser degrees, the science is clear, and we’re dragging our feet on solving the problem.

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