Published online by Ugo Bardi http://cassandralegacy.blogspot.co.uk/2012/04/methane-and-disturbed-carbon-cycle.html
A profoundly useful follow up piece by Ugo covers the large scale CARBON CYCLE and earth temperature control, only briefly referred to in my piece and in my endnote. Ugo is here http://cassandralegacy.blogspot.co.uk/2012/05/great-chemical-reaction-life-and-death.html
Methane and the disturbed Carbon Cycle
A look at recent studies in climate science
Guest Post by Philip Harris
(a longer version of this post is available here)
Philip Harris is a retired plant
scientist based near the Scottish border in the UK. He has worked for
government agencies in such areas as food safety and plant quarantine
and disease diagnostics, and on risk identification and risk assessment.
From 1997 to 2006 he worked for the EU on 'capability-building'
science projects in ex-communist countries of Europe.
The Kilda Basin, located between
Scotland and Norway. This basin may have suddenly released such a large
amount of methane in the atmosphere that it generated the
"Paleocene-Eocene thermal Maximum" (PETM), an episode of rapid global
warming that took place about 55 million years ago. Could this episode
be a model of what may happen in the near future with the rapid release
of methane observed today? This point is discussed by Philip Harris in
this post. (image above from Nisbet et al. 2009 - ref (7))
Preface by Ugo Bardi
A few months ago, I published a post on "Cassandra's Legacy" titled "Methane Hydrates: the next communication bomb"
where I argued that the possibility of a catastrophic release of
hydrates (the so-called "clathrate gun hypothesis" is going to have a
massive impact on the debate on climate change. In this and in other
posts, I have been arguing that we are facing a task that we cannot
leave to climate scientists alone. A
ll
of us must tackle the issue; understand it, and give our
contribution to alert everybody of the risks ahead. It is only in this
way that the problem can gain the attention of the public and policy
makers together. These posts of mine led to a response by Philip Harris,
retired plant scientist, who agreed that we need to work on this
subject and who offered to produce a paper where he summarizes his
personal research on the subject. In
particular, Phil has examined the "Kilda Basin hypothesis." This term
refers to a region in the Atlantic Ocean, approximately between Scotland
and Norway. The idea is that the basin may have suddenly released large
amounts of greenhouse gases and forcing the disastrous episode of
global warming known as "Paleocene-Eocene Thermal Maximum" (PETM). The
story is described by Nisbet et al. in a 2009 paper in "Nature
Geoscience" (7). What is happening now with the human-caused release of
greenhouse gases may be similar to the conditions that led to the PETM
event.
What follow is a short version of Phil Harris' work, a complete version can be found on the site of ASPO-Italy.
Introduction: a personal quest
“Ugo
… At least I
should try. If we understand sufficiently the science story, we should
teach and encourage others to enquire.
The importance of the non-condensing gases becomes clearer.
Through our own intellectual struggle we occasionally find a dawning reality.
The mental act of adding modern CO2 and CH4 numbers on to
that figure of Hansen & Sato's was such a moment for me.
It also prepared me for The Kilda Basin Conjecture.
We are becoming already an exhaling ‘Kilda Basin’?
This stuff got a
'human reaction' from me, which might be communicable.”
The methane problem
Recently Ugo Bardi
raised the matter of methane and the fact that compared with geological
history, the present level in the atmosphere of this potent ‘greenhouse-gas’ is
exceptionally high. We see methane bubbling from the arctic margins. We know
the present level is around 1800 parts per billion (1.8ppm); more than 2.5-fold
the pre-industrial level. We know this rise has been sudden and that most of it
occurred in the 20thC up to about year 1990, and that interestingly for a
rapidly oxidised molecule, this high level has been sustained, and lately has
begun to increase again. After a brief discussion
with Ugo, I decided to attempt an update of my own knowledge. I needed also to
integrate knowledge of methane with understanding the role of the chief non-condensing
‘greenhouse-gas’, carbon dioxide.
What I have
experienced in the last few weeks has not been exactly a ‘Damascene’ moment,
but as we all know, if we struggle hard enough intellectually then a new awareness
of reality can dawn. Twenty and more years ago I had collected scientific
papers that addressed the importance of atmospheric methane. This gas was
already well understood to be part of the more general human-induced inflation
of radiative forcing in the climate. We have dramatically increased the
non-condensing ‘greenhouse’ gases in the earth’s atmosphere. It is a matter of
fact that we experience extra radiative forcing (net trapped sunlight) because
of these ‘trace’ gases released by industrialisation and in the case of methane
also arising from the recent large extension of agriculture. We have for
decades been able to watch the ongoing rise of carbon dioxide (CO2) measured
continuously by NOAA Observatory in Hawaii. Methane (CH4), the
second most important of the non-condensing gases was known to have increased even
more dramatically from pre-industrial levels. All this we knew decades ago. And,
already twenty years ago the ice and sediment records were beginning to tell
their stories of past climates.
Where has the
relevant science gone over the intervening 20 years? Can I interest you, the reader, in my recent journey of discovery,
and particularly in what for me were the illuminating and I hope insightful
moments?
I
wrote a longer article in order to convince myself that I had sufficiently
grasped the later scientific evidence and scientific arguments, and I used many
quotes from and references to scientific papers: this longer article is
available at the ASPO website if you want to engage more with the details. I
would value additions, comments and corrections.
Firstly I
familiarised myself again with the carbon cycle (‘sources and sinks’) and then with
the way it has changed over geological time, so that I could better place in
this context the vast “meta-stable” reserves of solid methane gas hydrates,
otherwise known as ‘clathrates’. These
are sequestered but potentially gaseous carbon deposits, which have been part
of the earth’s carbon cycle for hundreds of millions years; maintained possibly
continuously, if dynamically, over this unimaginably long history. More
recently, clathrates have been part of a relatively
stable, though oscillating, carbon cycle and climate. These oscillating cycles
have been ‘normal’ for a million or more years. As the climate oscillates, so
does the carbon cycle along with the consequent hydrological cycle. The earth during
this period has oscillated from glacial era to part-glacial era and correspondingly
the sea level has gone up and down by some 120 to 130m. Our kind has become
used to the latest extended warm period since the sea level last rose by about 120m
about 10,000 years ago.
We can ask, though, how the great stores of methane
clathrates have interacted with climate changes not only in the last million
years, but also much further back. What do we know from the records of longer
geological time? Calculations have revealed that even a small fraction of the
probable reserves if they were suddenly released into the atmosphere could
overwhelm the photo-oxidation (OH’) capacity of the atmosphere and thereby persist
for long enough to cause a great pulse of warmth from trapped sunlight. Indeed
it was a long time ago, about 55 million years ago, but something like this actually
seems to have happened. The result then was to initiate a disordered carbon cycle that lasted 100,000 years and a ‘thermal maximum’ climate we would not
recognise – the PETM.
Toward
the end of this present shorter article I draw your attention to the ‘Kilda Conjecture’. Nisbet et al Nature 2009, see below, make the
case that repeated exhalations of methane and carbon dioxide from an ancient
ocean basin they name 'Kilda', could 55
million years ago, have kick-started
the profound disorder in the carbon cycle seen in the geological record, the PETM; a
disorder known to have lasted about 100,000 years. These authors draw parallels
with the present extended exhalations of greenhouse gases from modern human
society.
1st
personal insight: comparability of the present day ‘trace’ gases with the
remote geological past
During the
PETM both CO2 and CH4 were maintained over millennia at
very high concentrations; methane at perhaps 5 to 10-fold those of the recent
pre-industrial concentrations. Numbers matter. To recapitulate; CH4
levels in the last few decades are
sustained 2.5-fold higher than pre-industrial concentrations. I will return to
the PETM but let me introduce another ‘moment’ that was for me one of increased
clarity.
2ndpersonal insight:
the importance of the non-condensing ‘trace’ greenhouse gases becomes clearer.
Snowball Earth and the non-condensing
gases
There was, a very long time
ago, a Snowball Earth; a period that ended around 635Ma. Gas hydrate releases
are mentioned as one of putative positive feedback mechanisms that brought this
phenomenon to an end.
[i] Hypotheses
accounting for the abruptness of de-glaciation include ice albedo feedback,
deep-ocean out-gassing during post-glacial oceanic overturn or methane hydrate
destabilization.
Scientific discussion continues
about this interesting period, but for our purposes it is worth noting the
reasons why we do not have a snowball earth.
[ii] Ample physical
evidence shows that carbon dioxide (CO2) is the single most important
climate-relevant greenhouse gas in Earth's atmosphere. This is because CO2,
like ozone, N2O, CH4, and chlorofluorocarbons, does not
condense and precipitate from the atmosphere at current climate temperatures,
whereas water vapour can and does.
Non-condensing greenhouse gases, which account for 25% of the total terrestrial
greenhouse effect, thus serve to provide the stable temperature structure that sustains the current levels of atmospheric water vapour
and clouds via feedback processes that account for the remaining 75% of the
greenhouse effect. Without the radiative
forcing supplied by CO2 and the other non-condensing greenhouse
gases, the terrestrial greenhouse would collapse, plunging the global climate
into an icebound Earth state (emphasis added).
Methane is
only a transient ‘trace’ gas, but we know that in recent decades it supplies about
20% of the extra net radiative forcing that results from ‘our’ extra
greenhouse gases in the atmosphere; a significant addition to the total
greenhouse effect.
3rdpersonal insight:
the enormity of the last few decades
Glacial
and Inter-Glacial Periods over the last 800,000 years
Before our present Holocene interglacial
there was the previous warmer Eemian (+1°C, 125,000 years ago), and before that the also warmer
Holsteinian (400,000 year ago). Greenhouse gases in the atmosphere rose then to
levels similar to recent pre-industrial Holocene levels.
Figure 1 800,000
years of CO2 and CH4 concentrations correspond
with timing of glacial/interglacial temperature fluctuations; from Hansen & Sato, 2011
Personally, I only get the enormity of what has happened in the
last few decades if I superimpose present CO2 and CH4 concentrations
(respectively 392ppm and approximately 1800ppb[iii])
on the end of the above figure (Hansen & Sato,2011[iv]).
Methane immediately after the end of the
Younger Dryas event was at ~700ppb; dropped to ~600ppb by 5000 years ago;
climbed to >700 again by the year 1750.)
I encourage you to re-enact my mental process and
superimpose your own visualisation.
4thpersonal insight:
comparisons over 5 million years are valid enough
A mere 5
million years ago in the Pliocene the ocean was about 25m higher than today,
but temperatures were not greatly higher than those in the inter-glacial Eemian
125,000 years ago, or those just now. However,
CO2 levels back then in the
Pliocene were higher than in the more recent one million year glacial period; i.e.
higher than pre-industrial levels in our Holocene (280ppm), but probably comparable with those of the
last 10 years at 380ppm. (See discussion in Hansen & Sato, 2011 ref. iv). Quote:
And regardless of the precise temperatures in the Pliocene,
the extreme polar warmth and diminished ice sheets are consistent with the
picture we painted above. Earth today, with global temperature having returned
to at least the Holocene maximum, is poised to experience strong amplifying
polar feedbacks in response to even modest additional global mean warming.
This is our
world as it is emerging. ‘Our’ CO2, though, has the potential to go
much higher than Pliocene levels, and is coupled at the same time with a
sustained exceptional methane level.
…. ****** ….
I have
collected a number of up-to-date studies that look at abrupt (millennial scale)
warm and cold climate events that occurred both during and at the termination
of the last glacial maximum. These studies consider the raised level of methane
(see again Figure 1, above), that accompanied both the earlier warmer excursions
and, finally, the glacial termination. The studies include an assessment of the
stability of marine clathrates and whether sudden release of methane might have
initiated the warm periods. Details are
in my longer article located here. Despite conjectures about the ‘Clathrate Gun’ (a sudden instability
of very large clathrate deposits) having initiated positive feed-back changes and
thus acted as a prompt cause of rapid climate warming events, marine hydrates actually
appear to have been generally stable during the glacial and inter-glacial
periods of the Pleistocene. Nevertheless, clathrates over this time have been to
a degree dynamic, especially in the Arctic. They either form or are released in
response to changing pressure/temperature combinations as the temperatures of
both ground and ocean adjust to the prevailing cooling or warming trend and as
the sea level falls or rises; … I quote from my longer article:
There is much of interest discussed
[refs.], but the take-home point just now might be that although past thermal
shocks must have gradually de-stabilised some CH4 gas hydrates, thus
both increasing chronic methane release and adding to warming events during
de-glaciations, these shocks did not cause sustained runaway temperatures
during the subsequent inter-glacial periods. Further methane-induced positive feedback did not happen. Vast
reserves of CH4 and other near-surface carbon still remained. For
example; the previous Eemian inter-glacial 125,000 years ago achieved a greater
global warmth (about +1°C with reference to year 2000, according to ocean
cores, see Hansen & Sato above), high enough to entail a 5m higher sea
level than at present, but did not provoke a self-stoking methane/CO2
release sufficient to prevent later re-glaciation. In the last very few
decades, however, humanity is administering a powerful thermal shock to a still
warm inter-glacial by inducing concentrations of non-condensing greenhouse
gases that are higher by a margin not seen in the past 2 – 5 million or more
years.
For those readers who are interested
in arctic methane and the basis for future studies, there is also in my longer article
an introductory discussion of a very recent publication: “Gas Hydrate Formation
and Dissipation Histories in the Northern Margin of Canada”, 2012. I have even
more recently read this paper
“On carbon transport and fate in the East Siberian Arctic land–shelf–atmosphere
system”, 2012, which makes a strong case for future monitoring of these
processes. As a ‘lay person’ I heartily endorse the authors’ case. Earlier
papers by Nisbet, 2002, and Archer, 2007, are also worth reading and links are
in my longer article.
…. ****** ….
5thpersonal insight:
atmospheric methane levels, and their impacts, depend on the rate of release
not on reserves
In my longer article I comment in more
detail on the calculations and thesis accompanying the ‘Kilda conjecture’
published in the journal Nature Geoscience; Nisbet, 2009 [Ref V
below].
Recent
calculations have assessed the quantities and the rate of release that would be
needed for a sustained methane-induced thermal shock to the climate, large
enough to lead to a runaway effect. The present dissipation of clathrates (or
other near surface organic sources of methane) to the air, is more likely to
remain chronic and will probably contribute to sustaining the high man-made
level of atmospheric methane, rather than, on its own, initiate runaway ‘positive
feedback’. (It can be assumed that in the absence of very high sustained
‘natural’ levels, future atmospheric CH4 levels would rapidly reduce
if methane release from fossil fuels was to stop.)
[v]The
period between gas release events (repeat time) needs to be comparable to, or
shorter than, the atmospheric residence time of the warming gas, otherwise the warming effect of one release
event will fade before the next event occurs. [Emphasis added.]
The snag, though, it seems is the continuing very large
man-made releases of both CH4 and CO2, particularly from remaining
fossil fuels, and the raised CO2 concentrations that will continue
long after most fossil fuels have been burned.
6thpersonal insight:
requirements for a disrupted carbon cycle and sustained climate disorder can be
described; for example, the Kilda conjecture
A massive climate impact, such as the start of a
disordered carbon cycle of the size-order of the Paleocene/Eocene Thermal
Maximum, PETM, would require a very large and sustained release of greenhouse
gases.
Ibid
ref V a recurrent release
of greenhouse gases is therefore required to explain the much longer-term
warming in the PETM. …
Even a large release from a single deep ocean clathrate
deposit, perhaps if it occurred because of volcanic action unrelated to climate
change, would not be enough to firstly interrupt and then promote
self-sustaining disorder of the carbon cycle. I quote from my own longer
article:
“In particular, single event methane
releases have been examined [by Nisbet et al. ref V] as putative trigger
events for a cascade leading to sustained high levels of atmospheric
non-condensing gases. Single releases from sources such as ocean floor hydrates
were/are not, individually, sufficiently large, nor did they recur frequently
enough, to act as trigger events for subsequent self-sustaining high
atmospheric concentrations, and these sources are rejected as explanations for
the ‘PETM trigger’. The authors, though, identify one possible singular source
of methane, the geologically brief Kilda Basin 55Ma. This basin apparently has no large modern parallel although some modern
Rift Valley conditions provide qualitative parallels. The ancient Kilda Basin
could have provided a single source large enough to suddenly overwhelm the
atmospheric OH’ oxidising sink and thus prolong for many decades the
atmospheric residence time of a massive methane release. Hence, the release
could have been big enough to promote a subsequent very prolonged period of both
high CO2 and CH4 concentrations. (It is possible that the
Kilda Basin might have produced recurrent exhalations). Plausibly the
trajectory to the inevitable PETM was begun in this way. The authors speculate:
Ibid ref V Unlike
other suggested triggers, bursts of methane and carbon dioxide from Kilda could
have been large enough, and could have been repeated frequently enough, to
initiate the persistent global warming throughout the PETM. Could the comparable injection of modern
anthropogenic emissions induce the same response from the planet? [Emphasis added.]
Remaining
queries:
Thus, for now, my remaining query will be: Are ‘we’ the modern ‘Kilda
Basin’?
Could ‘we’ be an initiating trigger like Kilda?
There are already signs of a disrupted carbon cycle as we lower the pH
in the ocean.
Modern rising CO2 levels are rising more rapidly and changing the ocean
more quickly than the slow changes recorded for the Pliocene a mere 5 million
years ago when CO2 was last near 390ppm in the atmosphere. [See footnote
and ref[vi]]
The configuration of the
continents, mountain ranges and ocean connections are different from those 55
million years ago. The PETM took (several) thousands of years to reach a
maximum. We can hope our descendents are spared.
Personally
I do not wish to even think about a future PETM equivalent, even if it is not
imminent for a thousand years. The current human-induced mass extinction of
biota and the emergence of a ‘New Climate’ are bad enough to contemplate, even
with scientific caveats about uncertainty. There
was a symposium in London at the Royal Society of Chemistry, Burlington House,
November 2-3, 2010, and abstracts are available on-line. Presentations reviewed
past Carbon Isotope Excursions, CIE’s, particularly the Palaeocene Eocene
thermal maximum (PETM, 55Ma), when discussion centred on these past ‘greenhouse
worlds’ and mass extinction events as analogues for future events and
ecologies. I refer you to the set of symposium
abstracts
and leave you with the safety instructions for Burlington House displayed
prominently at the end of the programme ’flyer’;
If you hear the Alarm
Alarm
Bells are situated throughout the building and will ring continuously for an
evacuation. Do not stop to collect your personal belongings.
[i] Snowball Earth termination by destabilization
of equatorial permafrost methane clathrate;
Kennedy M, Mrofka D, von der Borch C. Nature, 2008 May 29; 453(7195):642-5.
[ii] Atmospheric CO2: principal control knob
governing Earth's temperature; Lacis A.A. et al. Science. 2010 Oct 15;330 (6002):356-9.
[iii] Global
atmospheric methane: budget, changes and dangers; Dlugokencky EJ, et al. Philos Transact A Math Phys Eng Sci. 2011 May 28; 369(1943):2058-72.
[iv] Paleoclimate
Implications for Human-Made Climate Change, Hansen & Sato, 2011, submitted
for publication. FULL PAPER
[v] Kick-starting
ancient warming; E. G. Nisbet et
al.; 2009, Nature Geoscience 2,
156 - 159 (2009)
[vi]
The Geological Record of Ocean Acidification, Bärbel Hönisch
et al, Science
2 March 2012: 335 no. 6072 pp. 1058-1063 ABSTRACT