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Catastrophic Methane Release Unlikely

Page history last edited by PBworks 12 years, 1 month ago

Hi Ross,

 

The idea of methane as a potentially catastrophic feedback to warming temperature is put out there by many but is there sound science to support such an idea?

 

See debate unfolding below

 

To attempt to understand this we need to look at paleoclimate to see

how methane has responded to previous warm periods. An interglacial

that was very similar to our Holocene is the MIS 11 interglacial from

420,000 years BP until 370,000 BP. During MIS 11 Milankovich forcing

was similar to our current Holocene. It was a very long and very warm

interglacial.

 

Here is a comparison of our current interglacial with MIS 11 from the

EPICA ice core:

 

http://www.nature.com/nature/journal/v429/n6992/images/nature02599-f5.2.jpg

 

As you can see global temperatures rose for thousands of years to be

much warmer that modern times. Sea level was much higher and the

Greenland ice sheet and West Antarctica Ice Sheet were much smaller at

that time. Greenland was so warm it had Spruce forrests (Steig and

Wolfe 2008).

 

So with a warmer and longer period how did methane react?

 

Here is a comment by Edward Brook from Tiny Bubbles Tell All:

 

"During MIS 11, an interglacial period between about 420,000 to

370,000 years ago, methane reached typical maximum levels, fell by

about 100 parts per billion over 5000 years, then rose again toward

the end of the interglacial period. This is similar to the pattern

over the past 10,000 years (14), which has been the subject of an

interesting argument over the impact of early human activities on the

atmosphere (15, 16)."

 

Tiny Bubbles Tell All

http://geo.oregonstate.edu/people/faculty/publications/brooke/Brook_TinyBubbles.pdf

 

Also from Dr. Brook is this graph from his paper 'Palaeoclimate:

Windows on the greenhouse'.

 

http://www.nature.com/nature/journal/v453/n7193/images/453291a-f1.2.jpg

 

Note that during previous warm periods methane increased but despite

a climate that was warmer than today for an extended period there was

no spike in methane.

 

Another example is the last interglacial period known as the Eemian or

MIS 5. This interglacial 123,000 BP was warmer than today with sea

levels 3 to 5 meters higher than today. Looking at the graph in the

link above the green methane line responds to temperature but despite

the very warm Eemian stayed in a small range, with a maximum of ~750

ppbv only slightly exceeding preindustrial levels of methane in our

atmosphere.

 

 

So from recent paleoclimate (the past half million years) we find no

examples of a warm climate causing a massive release in methane.

Methane is currently 3 times the normal from previous interglacials

with no reason it should significantly increase.

 

There are also methane clathrates, a solid form of water with methane

that are on the ocean floor and buried in some bogs. This is

potentially a huge source of methane, but again there has never been a

case when a warm climate triggered a release. It is thought that there

was one case of a massive release of methane clathrates, at the

Paleocene-Eocene Thermal Maximum 55 million years ago.

 

This was a huge event. According to Gavin Schmidt:

 

"The change at the PETM was so large that it would have required a

decrease in biological activity equivalent to roughly three times the

total present-day terrestrial biosphere. In other words, if all of the

terrestrial carbon today (in forests, animals, soils, etc.) were

converted to carbon dioxide and returned to the global inorganic

carbon pool, the change in the global carbon isotopic ratio would only

be a third as big as that observed during the PETM!"

 

http://www.giss.nasa.gov/research/briefs/schmidt_02/

 

To attempt to understand the potential for such an event to occur

again we need to look at what caused this release of methane

clathrates. According to Storey et al 2007, 'Palocene-Eocene Thermal

Maximum and the Opening of the Northeast Atlantic' the cause was

"volcanic eruptions that created the North Atlantic Ocean when

Greenland and northwestern Europe separate".

 

http://news.mongabay.com/2007/0426-petm.html

 

The oceans were dramatically heated, huge amounts of CO2 were emitted

and this destabilized methane clathrate deposits on the ocean floor.

 

Looking back over the historical evidence methane emissions do respond

to increased temperature but there is no case where this has caused a

massive feedback and during the interglacials of the past half million

years that were warmer than today we see no sign of increased methane

release. Our atmosphere already has 3 times the previous natural

levels of methane showing that anthropogenic emissions dwarf natural

emissions, the only exception to this was an extreme example where the

ocean floor was literally splitting apart during the PETM.

 

Based on this I would characterize the talk of methane as a major

feedback to be alarmism.

 

Science based comments are welcome.

 

Cheers

 

Jim

 

 

The previous warmings are not comparable because the temperature

increases were much much more gradual. With gradual warming, only

small sections of permafrost in any one decade would have begun to

release methane, and with about a 12 year half-life for oxidation to

carbon dioxide, and slow increases in carbon dioxide so that the sinks

would work well, it is logical that the methane level would not have

gotten very high.

 

However, the temperature rise is now very rapid, so large tracts of

permafrost are being rapidly warmed to release large amounts of

methane. We are also overwhelming our sinks with the fossil fuel burning.

 

We need a scientific group to try to quantify this difference with

appropriate computer models.

 

But in the meantime, there is no adequate scientific reason to say

that just because there was not a major increase in methane in

previous slow warming periods, there will not be a major increase in

our current extremely rapid warming period.

 

Jim

 

Hi Jim,

 

--- In ClimateConcern@yahoogroups.com, "James F. Newell"

wrote:

>

> The previous warmings are not comparable because the temperature

> increases were much much more gradual. With gradual warming, only

> small sections of permafrost in any one decade would have begun to

> release methane, and with about a 12 year half-life for oxidation

> to carbon dioxide, and slow increases in carbon dioxide so that the

> sinks would work well, it is logical that the methane level would

> not have gotten very high.

>

 

Actually methane changes are consistently seen in the paleoclimate

history. Methane may have a 12 year half-life but when it is released

it tends to be released in quantities. Also climate tends to cool in

slow steps but warm quite rapidly.

 

A good example is at the Younger Dryas transition, a very rapid

cooling and then after a 1,000 years of near ice age warmed more than

10 degrees C in less than 50 years. Methane did increase, roughly 350

ppbv during that period of actual rapid climate change and returned to

typical interglacial levels.

 

Going back further, Dansgaard-Oeschger Events during the past ice age

were also rapid climate events accompanied by a release of methane.

Concentrations jumped as much as 200 ppmv at that time.

 

A few references:

Ice-core evidence of abrupt climate changes

http://www.pnas.org/content/97/4/1331.full

 

Vostok Temperature and Methane Graph

http://www.giss.nasa.gov/research/features/methane/core1.gif

 

Also interesting is this study which shows that the large methane

increase was not from "tropical wetlands or from plant" and not

seafloor methane deposits:

 

http://www.eurekalert.org/pub_releases/2006-08/osu-sro082106.php

 

This similar study agrees:

 

http://www.eurekalert.org/pub_releases/2008-04/haog-mso041508.php

 

"The isotopic measurements show no signs of CH4 emissions by a

destabilization of marine gas hydrate reservoirs when climate was

warming."

 

So there is no evidence of a methane clathrate release of any

significance since the PETM and to forecast any such release due to

climate change would not be based on anything factual but simply alarmism.

 

 

It is also important to look at the historical range of methane when

compared to today. Looking at the Vostok ice core (above) methane

moved in a range of ~ 400 ppbv to ~ 800 ppbv with the changes driven

by the warming and cooling of the earth (primarily though sea level

changes and increased/decreased wetlands). Today methane is 1760ppbv,

far above any natural methane release ever seen.

 

http://www.giss.nasa.gov/research/features/methane/core2.gif

 

So with mankind already increasing methane far above any time of the

past 600,000 years there is nothing to support a further increase due

to warming climate and any natural release would be a small percentage

of our already historically high methane level.

 

> However, the temperature rise is now very rapid, so large tracts of

> permafrost are being rapidly warmed to release large amounts of

> methane.

 

We frequently see talk of how rapid climate change is, or that past

climate change was much more gradual but it is simply not true. This

decade particularly we are not seeing continued warming. But let's

look at the recent warming as a whole.

 

Here is a graphic from the Hadley Centre CRU.

 

http://www.metoffice.gov.uk/corporate/pressoffice/myths/Forcing-Diagram.gif

 

The purpose of this diagram is to show that models can reproduce the

early 20th century warming by natural forcing alone but not the

warming of the latte half of the 20th century.

 

Notice that the natural warming trend of the first half of the 20th

century is of the same slope as the only warming period attributed to

AGW, the period 1979 to 1998. This shows us that the period attributed

to AGW is no more rapid than the most recent natural warming phase and

definitely cannot be considered rapid when compared to actual rapid

warming periods of the past such as the Younger Dryas transition.

 

The last decade we definitely cannot talk about how rapid the

temperature rise is with the relatively steady temperature we have seen.

 

http://www.globalwarmingart.com/images/a/af/Short_Instrumental_Temperature_Record.png

 

So with research showing no release of methane clathrates from

previous climate warming and with the relatively small releases of

methane that did exist being dwarfed by methane from our civilization

I will again state that the talk of a methane release as a major

feedback to AGW is pure alarmism with no basis in sound science.

 

Again science based responses are welcome, however please don't simply

insist something without any scientific basis in fact.

 

Cheers

 

Jim

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