Showing posts with label arctic. Show all posts
Showing posts with label arctic. Show all posts

Wednesday, May 20, 2015

Kelp Farming and Ice Dyking

Aaron Franklin
Kelp farming and ice dyking for habitat enhancement 
and carbon-negative fuels and chemical production.

By Aaron Franklin

A purpose-built craft like this Ground effect plane / hovercraft triphibian concept could be ideal.

The laterally-rigid sideskirts with vertically-flexible surface-contouring ski bottoms would allow transitions between air, water, ice, snow, earth surfaces of all types and the waterscoop tail could directly hose the water onto the ice with foil effect to counter lateral reaction thrust. Snow making, firefighting, and ecology seeding also in its functionality.


At pumping of 10tons per second, 50m x 100m/s = 5000sqm, 10000kg/5000sqm = 2 kg per sqm per pass. About 2mm per pass.

If we assume conditions that will allow 2 mm to freeze in 30 seconds. then 4mm per minute = 240mm per hour = 5760mm (near 6m thick) per day could be made of 50m wide by 100m/s x 30s = 3km long of icedyke by a mobile spray vehicle at 100m/s.

3000m x 6m x 50m = 900 000 tons per day of ice making.

A fleet of 50 working for 100 days therefore could make 5000 x 900 000 = 45 000 000 000 tons or near 5 cubic kilometers of ice. 

If we are looking at an average needed to ground them of say 30m thick, then 50m wide is cross section area of 1500 sqm.

5 000 000 000 cubic m / 1500 sqm = 3.33333 million meters or 3333 km.

A ball park figure of 1000kw vehicle power would seem adequate to do this.

Very likely a rope mesh reinforcement would need to be floated on the water and anchored in place to hold together the dyke that has been formed. Doing this work in polynyas seems the best way, then towing into position of sections to be anchored and further thickened.

If 100 such vehicles were used you've got near seven thousand km of icedyke which could be enough for such a layout as this:
Kelp farming, by Aaron Franklin, on background image by Shakhova et al., 2010

For methane plume hotspots to the surface, hexagonal tiles would need to be formed and towed into place, if they are too rich for ice to form inside the rings in situ.

Stationary pumping systems might have to high costs per area in most places with limits to small volumes per pump due to area feasible to distribute the water to and ice layup rates. Though in saying this, high cost is often seen as a benefit for commercial interests. They can make more money doing it the hard way.

The purposes of kelp farming in the less methane emissive areas is as follows:
  • Biomass for biofuels and biochemicals of around 500 ton per hectare per year can be harvested.
  • The growing kelp oxygenates the water to support consumption of methane and river in-flux of organic carbon.
  • The artificial kelp forests provide habitat and food for a diverse and rich ecology with fisheries and abalone/ mussel/ crabs / lobster etc farming potential
  • Unlike micro algae, the kelp biomass is easily harvested, so it would not rot and cause oxygen depletion of the water at the end of summer.
  • Sedimentation rates and water clarity are vastly improved by the kelp forests, thereby improving albedo and enhancing natural carbon burial in sediments.
  • Simple and low cost infrastructure only is neccessary to process the kelp locally into liquids for low transport costs to refineries for further upgrading.
  • It would be easy to use the CO2 from an initial biomass pyrolysis to convert methane collected nearby to methanol for easy low cost transportation.
Combining these systems would allow zero carbon emission liquid fuels via the energy component of the fossil methane and biomass being used as hydrogen and the carbon turned into biochar and high performance bioglues and recyclable polymers, allowing further long-term carbon sequestration by wood, biofibre, etc., and component for construction materials, also replacing high carbon-emission steel, concrete etc.

Sunday, April 26, 2015

Save the Arctic



by Renaud de Richter










Links

- This idea was proposed by Denis Bonnelle,
'Solar Chimney, water spraying Energy Tower, and linked renewable energy conversion devices: presentation, criticism and proposals', p120-125.
PhD thesis 9 July 2004, university Claude Bernard, Lyon, France, registration n°129-2004.
http://data.solar-tower.org.uk/thesis/2004-Denis-BONNELLE_Solar-chimneys_Energy-towers_etc.pdf


- For more ideas, see: 
Fighting global warming by climate engineering: Is the Earth radiation management and the solar radiation management any option for fighting climate change?
By Tingzhen Ming, Renaud de_Richter, Wei Liu and Sylvain Caillol
http://www.sciencedirect.com/science/article/pii/S1364032113008460


Friday, December 13, 2013

Ocean Tunnels


Ocean tunnels are proposed by Patrick McNulty as a way to combat global warming. Many of these tunnels, lined up across the Gulf Stream and the Kuroshio Current, could supply large quantities of clean energy to the North American East Coast and to East Asia.

Such tunnels can supply energy continuously, i.e. 24 hours a day, all year, making them suitable to supply base load energy as currently generated by coal-fired power plants and nuclear power plants. 

Ocean tunnels thus hold the potential to supply huge amounts of clean energy and facilitate a rapid move to a sustainable economy, as part of the comprehensive and effective action needed to combat climate change. This is pictured in the image below under part 1. 

Comprehensive and effective action is discussed at the Climate Plan blog

Ocean Tunnels can be combined with Ocean thermal energy conversion (OTEC) methods that use the temperature difference between cooler deeper parts of the ocean and warmer surface waters to run a heat engine to produce energy. Once such a system is in place, it has access to both deeper parts of the ocean and to surface waters, while generating a lot of energy. Such a system can also be used to pull up sunken nutrients from the depth of the ocean and put them out at surface level to fertilize the waters there, while the colder water that is the output of OTEC will float down, taking along newly-grown plankton to the ocean depths before it can revert to CO2, as described in the earlier post Using the Oceans to Remove CO2 from the Atmosphere.

Tunnels could regulate temperatures in the Arctic in a number of ways. The clean electricity they generate can replace ways polluting energy that warms up the Arctic. The clean energy tunnels generate can also be used in projects that help reduce temperatures in the Arctic. Furthermore, the turbines in tunnels can reduce the flow of ocean currents somewhat, thus reducing the flow of warm water into the Arctic.

Additionally, tunnels also hold the potential to divert warm water elsewhere and to move colder water into places that could otherwise get too warm, i.e. part 2. (Heat management) of the above action plan, more specifically management of water temperature.

Tunnels could be shaped to guide the flow of water into a specific direction, which could divert some of the water that is currently going into North Atlantic Current towards the Arctic Ocean down a southwards course along the Canary Current along the coast of West Africa.

Thus, tunnels could both produce energy to pump water elsewhere, or to pump water onto the sea ice and glaciers, to thicken the ice, or to pump sea water up into the air to spray it around and create clouds. The energy could be used in projects to help reduce temperatures in the Arctic. Additionally, tunnels could also be shaped in ways to guide water, which works even when no energy is generated. Tunnels is a concept with many applications and testing and further studies will show which applications are attractive.

A comprehensive action plan will need to consider a wide range of action. A warming Arctic results in changes to the Jet Stream, in turn making that more extreme weather can be expected, as illustrated by the video below, by Paul Beckwith


In July 2013, water off the coast of North America reached 'Record Warmest' temperatures and proceeded to travel to the Arctic Ocean, where it is still warming up the seabed, resulting in huge emissions of methane from the Arctic Ocean's seafloor.
NOAA: part of the Atlantic Ocean off the coast of North America reached record warmest temperatures in July 2013
Diversion of ocean currents could reduce warming of the waters in the Arctic. As the image below shows, warm water is carried by the Gulf Stream all the way into the Arctic Ocean.



Warming up of the waters in the Arctic is threatening to cause release of huge quantities of methane that is held in sediments under the seabed, as discussed in the post Quantifying Arctic Methane.


References

- Climate change: Solutions to a big problem

- Arctic Methane Release and Rapid Temperature Rise are interlinked

- Causes of high methane levels over Arctic Ocean

- Quantifying Arctic Methane

Saturday, January 5, 2013

How to avoid mass-scale death, destruction and extinction

Climate change threatens to develops in four ways:
  1. Global warming
  2. Accelerated warming in the Arctic
  3. Runaway global warming
  4. Extinction
Warming accelerates in the Arctic due to a number of feedbacks, ten of which are depicted in the Diagram of Doom.

One of these feedbacks, methane releases from the Arctic seabed, constitutes a point-of-no-return, in that this threatens to trigger further releases in a vicious cycle that will escalate into runaway global warming. The combined impact of land degradation, storms and heatwaves will then cause crop and vegetation loss at unprecedented scale, resulting in mass death, destruction and extinction.

High food prices have been around for a few years, as illustrated by the FAO Food Price Index below (see interactive version of this image).



The FAO, in its recent Cereal Supply and Demand Brief, explains that we can expect prices to rise, as illustrated below.


The Economic Research Service of the U.S. Department of Agriculture mentions, in its Food Price Outlook, 2012-2013, that the "drought has affected prices for corn and soybeans as well as other field crops which should, in turn, drive up retail food prices".

Global food supply is under stress as extreme weather becomes the new norm. Farmers may be inclined to respond to drought by overusing ground water, or by slashing and burning forest, in efforts to create more farmland. Such practices do not resolve the problems; instead, they tend to exacerbate the problems over time, making things progressively worse.

The diagram below shows that there are many climatological feedbacks (ten of which are named) that make climate change worse. At the top, the diagram pictures vicious cycles that are responses by farmers that can add to make the situation even worse. Without effective action, the prospect is that climate change and crop failure combine to cause mass death and destruction, with extinction becoming the fourth development of global warming.

How can we avoid that such a scenario will eventuate? Obviously, once we are in the fourth development, i.e. mass-scale famine and extintion, it will be too late for action. Similarly, if the world moves into the third development, i.e. runaway global warming, it will be hard, if not impossible to reverse such a development. Even if we act now, it will be hard to reverse the second development, i.e. accelerated warming in the Arctic.

The most effective action will target causes rather than symptoms of these developments.

Part 1. Since emissions are the cause of global warming, dramatic cuts in emissions should be included in the first part of the responses. In addition, action is needed to remove excess carbon dioxide from the atmosphere and oceans. Storing the carbon in the soil will also improve soil quality, as indicated by the long green arrow on the left.

Part 2. Solar radiation management is needed to cool the Arctic.

Part 3. Methane management and further action is needed, e.g. to avoid that methane levels will rise further in the Arctic, which threatens to trigger further releases and escalate into runaway global warming. Measures to reduce methane can also benefit soil quality worldwide, as indicated by the long green arrow on the right.

Thus, the proposed action tackles the prospect of mass death and extinction by increasing soil fertility, as illustrated by the image below.


Depicted at the bottom of the image are the most effective policies to accomplish the goals set out in the proposed 3-part plan of action, i.e. feebates, preferably implemented locally. Cost associated with solar radiation management is relatively small, so relatively small fees, e.g. on commercial international flights could raise the necessary funding.

Thursday, November 29, 2012

A Comprehensive Plan of Action on Climate Change


Threat to global food supply makes comprehensive action imperative
Climate change is strongly affecting the Arctic and the resulting changes to the polar vortex and jet stream are in turn contributing to extreme weather in many places, followed by crop loss at a huge scale.

The U.N. Food and Agriculture Organization (FAO) said in a September 6, 2012, forecast that continued deterioration of cereal crop prospects over the past two months, due to unfavourable weather conditions in a number of major producing regions, has led to a sharp cut in FAO’s world production forecast since the previous report in July.

The bad news continues: Based on the latest indications, global cereal production would not be sufficient to cover fully the expected utilization in the 2012/13 marketing season, pointing to a larger drawdown of global cereal stocks than earlier anticipated. Among the major cereals, maize and wheat were the most affected by the worsening of weather conditions.

The image below is interactive at the original post and shows the FAO Food Price Index (Cereals), up to and including August 2012.

from: Threat to global food supply makes comprehensive action imperative
Apart from crop yield, extreme weather is also affecting soils in various ways. Sustained drought can cause soils to lose much of their vegetation, making them more exposed to erosion by wind, while the occasional storms, flooding and torrential rain further contribute to erosion. Higher areas, such as hills, will be particularly vulnerable, but even in valleys a lack of trees and excessive irrigation can cause the water table to rise, bringing salt to the surface.

Fish are also under threat, in part due to ocean acidification. Of the carbon dioxide we're releasing into the atmosphere, about a third is (still) being absorbed by the oceans. Dr. Richard Feely, from NOAA’s Pacific Marine Environmental Laboratory, explains that this has caused, over the last 200 years or so, about a 30% increase in the overall acidity of the oceans. This affects species that depend on a shell to survive. Studies by Baumann (2011) and Frommel (2011) indicate further that fish, in their egg and larval life stages, are seriously threatened by ocean acidification. This, in addition to warming seawater, overfishing, pollution and eutrification (dead zones), causes fish to lose habitat and is threatening major fish stock collapse.

Without action, this situation can only be expected to deteriorate further, while ocean acidification is irreversible on timescales of at least tens of thousands of years. This means that, to save many marine species from extinction, geoengineering must be accepted as an essential part of the much-needed comprehensive plan of action.

Similarly, Arctic waters will continue to be exposed to warm water, causing further sea ice decline unless comprehensive action is taken that includes geoengineering methods to cool the Arctic. The threat that huge amounts of methane will be released from the warming Arctic seabed makes it imperative to prepare geo-engineering methods to respond to this threat and be ready for rapid deployment soon.

How to avert an intensifying food crisis

As extreme weather intensifies, the food crisis intensifies. Storms and floods do damage to crops and cause erosion of fertile topsoil, in turn causing further crop loss. Similarly, heatwaves, storms and wildfires do damage to crops and cause topsoil to be blown away, thus also causing erosion and further crop loss. Furthermore, they cause soot, dust and volitale organic compounds to settle on snow and ice, causing albdeo loss and further decline of snow and ice cover.

Extreme weather intensifies as the Arctic warms and the polar vortex and jet stream weaken, which is fueled by accelerated warming in the Arctic. There are at least ten feedbacks that contribute to further acceleration of warming in the Arctic and without action the situation looks set to spiral away into runaway global warming, as illustrated by the image below.

Diagram of Doom, with Comprehensive Plan of Action added  (credit: Sam Carana, October 9, 2012)



To avert an intensifying global food crisis, a comprehensive plan of action is needed, as also indicated on the image. Such a plan should be comprehensive and consider action in the Arctic such as wetland management, ice thickening and methane management (methane removal through decomposition, capture and possibly extraction).

A Comprehensive Plan of Action on Climate Change

A Comprehensive Plan of Action on Climate Change needs to include policies to achieve a sustainable economy, as well as adaptation policies.

Such a comprehensive plan is best endorsed globally, e.g. through an international agreement building on the Kyoto Protocol and the Montreal Accord. At the same time, the specific policies are best decided and implemented locally, e.g. by insisting that each nation reduces its CO2 emissions by a set annual percentage, and additionally removes a set annual amount of CO2 from the atmosphere and the oceans, followed by sequestration, proportionally to its current emissions.

Policy goals are most effectively achieved when policies are implemented locally and independently, with separate policies each addressing a specific shift that is needed in order to reach agreed targets. Each nation can work out what policies best fit their circumstances, as long as they each independently achieve agreed targets.

Cuts in CO2 emissions of 80% by 2020 can be achieved by implementing local policies focusing on specific sectors (such as energy production, transport, land use, waste, forestry, buildings, etc).

As an example, each nation could add fees on jetfuel. Where an airplane lands that comes from a nation that has failed to add sufficient fees, the nation where the airplane lands could impose supplementary fees and use the revenues to support methods that capture CO2 directly from ambient air. Such supplementary fees should be allowed to be imposed under international trade rules.

Some policies will need to continue beyond 2020, in order to bring down levels of greenhouse gases in the atmosphere to their pre-industrial levels this century, i.e. getting CO2 in the atmosphere back to 280ppm, CH4 back to 700ppb and N2O back to 270ppb. Policies can be very effective when focusing on local sectors such as agriculture and buildings, while also supporting geo-engineering methods such as biochar, enhanced weathering and direct capture of carbon from ambient air.

In addition to such policies to achieve a sustainable economy and adaptation policies, further geo-engineering methods will be needed to avoid runaway warming, as indicated in the blue area of the image below.


Arctic Methane Management

At the original post, some of the areas in these images can be clicked on, for examples or more background. The box for Additional Arctic Methane Management on above image is further worked out in the image below, which highlights the need for geo-engineering methods that focus on methane, a component of the plan that needs to be given far more attention. Again, support for such methods could be agreed to proportionally to each nation's current emissions.

Friday, February 10, 2012

January 2012 shows record levels of methane in the Arctic

In January 2012, methane levels in the Arctic reached levels of 1870 ppb. 


Particularly worrying is that, in the past, methane concentrations have fluctuated up and down in line with the seasons. Over the past seven months, however, methane has shown steady growth in the Arctic. Such a long continuous period of growth is unprecedented, the more so as it takes place in winter, when vegetation growth and algae bloom is minimal. The most obvious conclusion is that the methane is venting from hydrates. 

Friday, February 3, 2012

How much time is there left to act?

How much time is there left to act, before methane hydrate releases will lead to human extinction? 

by Malcolm Light, edited by Sam Carana

 

Figure 1 below looks at the temperature impact of abrupt methane releases, as measured in 2010 in Svalbard (above image). Such emissions are typically triggered by disruption of the integrity of the hydrates holding the methane.



As the red line on the graph indicates, these emissions would raise local temperatures significantly, in a matter of months, since methane has a strong greenhouse effect.

At the time, the rapid increase in methane levels alarmed scientists around the world, but NASA now regards these releases merely as a local peak event that had little impact on overall global temperatures. Even so, the Svalbard event is indicative of the local temperature impact of such emissions.

The IPCC estimates the temperature change at 2090-2099 (relative to 1980-1999) at between 1.8°C (likely range: 1.1°C to 2.9°C) and 4.0°C (likely range: 2.4°C to 6.4°C), depending on the chosen scenario.

There are several ways to project how much temperatures will rise in future. The chart below shows the global temperature rise from 1980 to 2011, using the most recent NASA data. Clearly, a simple linear extension of this trend would not suffice, as it would ignore the many feedback effects accelerating the rise.


The worst-case IPCC scenario projects a mean temperature rise that would take average global temperature beyond 20 degrees Celsius this century, an obviously catastrophic scenario. Yet, the IPCC scenarios fail to include the many feedbacks that accelerate temperature rises, such as large abrupt releases from methane hydrates. In fact, the IPCC miserably failed to warn about the dramatic loss of Arctic sea ice, as pictured on the chart below, by Wipneus based on PIOMAS data.




Mid-point IPCC projections have been incorporated in Figure 2 below for reference. The diagram also incorporates the warming impact of large methane releases, triggered by a scenario based on the data from Svalbard and by the impact of increased seismic activity in the Arctic. 


Above updated global warming extinction diagram was produced using new information from the ice cap melting curve and the measured Svalbard methane concentrations (NOAA 2011a). 

While the gradients were calculated in a different way, taking account of existing Arctic temperatures, the result is almost identical to the earlier version. Furthermore, methane would only require to have a global warming potential of 43.5 over 50 years duration (Figure 2, duration from Carana 2011g) to achieve this high temperature increase in the Arctic.  The Arctic ice cap heating curves lag behind the expected Arctic atmospheric temperature curves by some 10 to 20 years over the defined extinction period which is probably a result of the extra energy needed for  the latent heat of melting of ice as the permafrost, Greenland and Antarctic ice caps melt away (Figure 2).

It is perfectly clear from the graphs that the methane build up in the Arctic is mainly a result of increasing earthquake activity along the Gakkel Ridge caused by global warming induced worldwide expansion of the Earth’s crust due to the carbon dioxide buildup in the atmosphere which is enhanced by the heating up of the Arctic ocean due to the high global warming potential of the methane (Light 2011). This close relationship between the Gakkel Ridge earthquake activity, the destabilisation of the Arctic methane hydrates and the NASA GISS surface temperature anomalies has already been clearly demonstrated (Carana, 2011b; Light 2011).

If I was a medical doctor I would say that the patient has a terminal illness and is expected to die of an extreme fever between 2038 and 2050. There are three actions that have to be taken immediately by world governments, if there is any faint hope of preventing the final excruciating stages of death the human race will be forced to live through as we are all boiled like lobsters.

  1. Developed (and some developing) countries must cut back their carbon dioxide emissions by a very large percentage (50% to 90%) by 2020 to immediately precipitate a cooling of the Earth and its crust. If this is not done the earthquake frequency and methane emissions in the Arctic will continue to  grow exponentially leading to our inexorable demise in 2038 to 2050. 
     
  2. Geoengineering must be used immediately as a cooling method in the Arctic to counteract the effects of the methane buildup in the short term. However, these methods will lead to further pollution of the atmosphere in the long term and will not solve the earthquake induced  Arctic methane buildup which is going to lead to our annihilation. 
     
  3. The United States and Russia must immediately develop a net of powerful radio beam frequency transmission stations around the Arctic using the critical 13.56 MHZ  beat frequency to break down the methane in the stratosphere and troposphere to nanodiamonds and hydrogen (Light 2011a) . Besides the elimination of the high global warming potential methane, the nanodiamonds may form seeds for light reflecting noctilucent clouds in the stratosphere and a light coloured energy reflecting layer when brought down to the Earth by snow and rain (Light 2011a). HAARP transmission systems are able to electronically vibrate the strong ionospheric electric current that feeds down into the polar areas and are thus the least evasive method of  directly eliminating the buildup of methane in those critical regions (Light 2011a).



References

IPCC Fourth Assessment Report on Climate Change 2007 - temperature rise projections
ipcc.ch/publications_and_data/ar4/wg1/en/spmsspm-projections-of.html

NASA global temperature data
data.giss.nasa.gov/gistemp/tabledata_v3/GLB.Ts.txt

Arctic Sea Ice yearly minimum volume, with trendline added by Wipneus, based on data by
Polar Science Center | Applied Physics Laboratory | University of Washington (2011) http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/

Carana, S. (2011b), Light M.P.R. and Carana, S. (2011c)
Methane linked to seismic activity in the Arctic
arctic-news.blogspot.com/p/seismic-activity.html

Light M.P.R. (2011), Edited by Sam Carana
Use of beamed interfering radio frequency transmissions to decompose Arctic atmospheric methane clouds
arctic-news.blogspot.com/p/decomposing-atmospheric-methane.html

Carana, S. (2011g)
Runaway Global Warming
geo-engineering.blogspot.com/2011/04/runaway-global-warming.html

Hansen, J.E. (2011)
GISS Surface Temperature Analysis. NASA. Goddard Institute for Space Physics
data.giss.nasa.gov/cgibin/gistemp/do_nmap.py?year_last=2011&month_last=08&sat=4&sst=1&type=anoms&mean_gen=02&year1=2009&year2=2009&base1=1951&base2=1980&radius=1200&pol=pol

IPPC (2007)
Fourth Assessment Report on Climate Change 2007. FAO 3.1, Figure 1, WG1, Chapter 3, p. 253.
blogs.ei.colombia.edu/wp-content/uploads/2010/12/graph-2-600X422.jpg

Light M.P.R. (2011)
Global Warming
globalwarmingmlight.blogspot.com

Masters. J. (2009)
Top Climate Story of 2008
www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1177

NOAA (2011a), generated ESRL/GMO – 2010, November 08, 11:12 am
Huge sudden atmospheric methane spike Arctic Svalbard (north of Norway)
The need for geo-engineering

NOAA (2011b), generated ESRL/GMO – 2011, December 14, 17:21 pm
Huge sudden methane spike recorded at Barrow (BRW), Alaska, United States.
The need for geo-engineering

Tuesday, January 10, 2012

The potential for methane releases in the Arctic to cause runaway global warming


What are the chances of abrupt releases of, say, 1 Gt of methane in the Arctic? What would be the impact of such a release?

By Sam Carana, December 20, 2011, updated January 10, 2012

How much methane is there in the Arctic?

An often-used figure in estimates of the size of permafrost stores is 1672 Gt (or Pg, or billion tonnes) of Carbon. This figure relates to organic carbon and refers to terrestrial permafrost stores. (1)

This figure was recently updated to 1700 Gt of carbon, projected to result in emissions of 30 - 63 Gt of Carbon by 2040, reaching 232 - 380 Gt by 2100 and 549 - 865 Gt by 2300. These figures are carbon dioxide equivalents, combining the effect of carbon released both as carbon dioxide (97.3%) and as methane (2.7%), with almost half the effect likely to be from methane. (2)

In addition to these terrestrial stores, there is methane in the oceans and in sediments below the seafloor. There are methane hydrates and there is methane in the form of free gas. 
Hydrates contain primarily methane and exist within marine sediments particularly in the continental margins and within relic subsea permafrost of the Arctic margins. (3)


Hunter and Haywood estimate that globally between 4700 and 5030 Pg (Gt) of Carbon is locked up within subsea hydrate within the continental margins. This does not include subsea permafrost-hosted hydrates and so those of the shallow Arctic margin (<~300m) were not considered. (3)

Shakhova et al. estimate the accumulated methane potential for the Eastern Siberian Arctic Shelf (ESAS, rectangle on image right) alone as follows:
- organic carbon in permafrost of about 500 Gt;
- about 1000 Gt in hydrate deposits; and
- about 700 Gt in free gas beneath the gas hydrate stability zone.
(4)  

The East Siberian Arctic Shelf covers about 25% of the Arctic Shelf (3) and additional stores are present in submarine areas elsewhere at high latitudes. Importantly, the hydrate and free gas stores contain virtually 100%  methane, as opposed to the organic carbon which the above study (2) estimates will produce emissions in the ratio of 97.3% carbon dioxide and only 2.7% methane when decomposing.

How stable is this methane?

The sensitivity of gas hydrate stability to changes in local pressure-temperature conditions and their existence beneath relatively shallow marine environments mean that submarine hydrates are vulnerable to changes in bottom water conditions (i.e. changes in sea level and bottom water temperatures). Following dissociation of hydrates, sediments can become unconsolidated, and structural failure of the sediment column has the potential to trigger submarine landslides and further breakdown of hydrate. The potential geohazard presented to coastal regions by tsunami is obvious. (3)

Further shrinking of the Arctic ice-cap results in more open water, which not only absorbs more heat, but which also results in more clouds, increasing the potential for storms that can cause damage to the seafloor in coastal areas such as the East Siberian Arctic Shelf (ESAS, rectangle on image left), where the water is on average only 45 m deep. (5)

Much of the methane released from submarine stores is still broken down by bacteria before reaching the atmosphere. Over time, however, depletion of oxygen and trace elements required for bacteria to break down methane will cause more and more methane to rise to the surface unaffected. (6)

There are only a handful of locations in the Arctic where (flask) samples are taken to monitor the methane. Recently, two of these locations showed ominous levels of methane in the atmosphere (images below). 






The danger is that large abrupt releases will overwhelm the system, not only causing much of the methane to reach the atmosphere unaffected, but also extending the lifetime of the methane in the atmosphere, due to hydroxyl depletion in the atmosphere.

Shakhova et al. consider release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time. (7)

What would be the impact of methane releases from hydrates in the Arctic? 


If an amount of, say, 1 Gt of methane from hydrates in the Arctic would abruptly enter the atmosphere, what would be the impact? 

Methane's global warming potential (GWP) depends on many variables, such as methane's lifetime, which changes with the size of emissions and the location of emissions (hydroxyl depletion already is a big problem in the Arctic atmosphere), the wind, the time of year (when it's winter, there can be little or no sunshine in the Arctic, so there's less greenhouse effect), etc. One of the variables is the indirect effect of large emissions and what's often overlooked is that large emissions will trigger further emissions of methane, thus further extending the lifetime of both the new and the earlier-emitted methane, which can make the methane persist locally for decades.

The IPCC gives methane a lifetime of 12 years, and a GWP of 25 over 100 years and 72 over 20 years. (8)

Thus, applying a GWP of 25 times carbon dioxide would give 1 Gt of methane a greenhouse effect equivalent to 25 Pg of carbon dioxide over 100 years. Applying a GWP of 72 times carbon dioxide would give 1 Gt of methane a greenhouse effect equivalent to 72 Pg of carbon dioxide over 20 years.

By comparison, atmospheric carbon dioxide levels rose from 288 ppmv in 1850 to 369.5 ppmv in 2000, for an increase of 81.5 ppmv, or 174 Pg C. (9)

Note that this 174 Pg C was released over a period of 150 years, allowing sinks time to absorb part of the burden. Note also that, as emissions continue to rise, some sinks may turn into net emitters, if they haven't already done so.

The image on the left shows the impact of 1 Gt of methane, compared with annual fluxes of carbon dioxide based on the NOAA carbon tracker. (10) 

Fossil fuel and fires have been adding an annual flux of just under 10 Pg C since 2000 and a good part of this is still being absorbed by land and ocean sinks. 

In other words, the total burden of all carbon dioxide emitted by people since the start of the industrial revolution has been partly mitigated by sinks, since it was released over a long period of time.

Furthermore, the carbon dioxide was emitted (and partly absorbed) all over the globe, whereas methane from such abrupt releases in the Arctic would - at least initially - be concentrated in a relatively small area, and likely cause oxygen depletion in the water and hydroxyl depletion in the atmosphere, while triggering further releases from hydrates in the Arctic.

This makes it appropriate to expect a high initial impact from an abrupt 1 Gt methane release, which will also extend methane's lifetime. Applying a GWP of 100 times carbon dioxide would give 1 Gt of methane an immediate greenhouse effect equivalent to 100 Pg of carbon dioxide. 

Even more terrifying is the prospect of further methane releases. Given that there already is ~5 Gt in the atmosphere, plus the initial 1 Gt, further releases of 4 Gt of methane would result in a burden of 10 Gt of methane. When applying a GWP of 100 times carbon dioxide, this would result in a short-term greenhouse effect equivalent to 1000 Pg of carbon dioxide.

In conclusion, this scenario would be catastrophic and the methane wouldn't go away quickly either, since this would be likely to keep triggering further releases. While some models project rapid decay of the methane, those models often use global decay values and long periods, which is not applicable in case of such abrupt releases in the Arctic.  

Instead, the methane is likely to stay active in the Arctic for many years at its highest warming potential, due to depletion of hydroxyl and oxygen, while the resulting summer warming (when the sun doesn't set) is likely to keep triggering further releases in the Arctic. 

References

1. Soil organic carbon pools in the northern circumpolar permafrost region 
Tarnocai, Canadell, Schuur, Kuhry, Mazhitova and Zimov (2009)
http://www.agu.org/pubs/crossref/2009/2008GB003327.shtml
http://www.lter.uaf.edu/dev2009/pdf/1350_Tarnocai_Canadell_2009.pdf

2. Climate change: High risk of permafrost thaw
Schuur et al. (2011)
Nature 480, 32–33 (1 December 2011) doi:10.1038/480032a
http://www.nature.com/nature/journal/v480/n7375/full/480032a.html
http://www.lter.uaf.edu/pdf/1562_Schuur_Abbott_2011.pdf

3. 
Science Blog: Submarine Methane Hydrate: A threat under anthropogenic climate change?
Stephen Hunter and Alan Haywood (2011)
http://climate.ncas.ac.uk/ncas-science-blog/241-science-blog-submarine-methane-hydrate-a-threat-under-anthropogenic-climate-change

4. Methane release from the East Siberian Arctic Shelf and the Potential for Abrupt Climate Change
Natalia Shakhova and Igor Semiletov (2010)
http://symposium2010.serdp-estcp.org/content/download/8914/107496/version/3/file/1A_Shakhova_Final.pdf


5. Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf
Shakhova et al. (2010)
http://www.sciencemag.org/content/327/5970/1246.abstract

6. Berkeley Lab and Los Alamos National Laboratory (2011)
http://newscenter.lbl.gov/feature-stories/2011/05/04/methane-arctic/

7. Anomalies of methane in the atmosphere over the East Siberian shelf: Is there any sign of methane leakage from shallow shelf hydrates? 
Shakhova, Semiletov, Salyuk and Kosmach (2008)
http://www.cosis.net/abstracts/EGU2008/01526/EGU2008-A-01526.pdf

8. Global Warming Potential
Intergovernmental Panel on Climate Change (IPCC, 2007)
http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-10-2.html#table-2-14

9. Runaway global warming 
Sam Carana (2011)
http://runawaywarming.blogspot.com


10. Carbon Tracker 2010 - Flux Time Series - CT2010 - Earth System Research Laboratory
U.S. Department of Commerce | National Oceanic & Atmospheric Administration (NOAA)
http://www.esrl.noaa.gov/gmd/ccgg/carbontracker/fluxtimeseries.php?region=All_Land#imagetable

11. On carbon transport and fate in the East Siberian Arctic land–shelf–atmosphere system

Saturday, December 24, 2011

Can we capture methane from the Arctic seabed?

Can we capture methane from the Arctic seabed?

Stephen H. Salter, School of Engineering, University of Edinburgh, Scotland. 

Prepared for the John Nissen Methane Workshop, Chiswick 15,16 October 2011.

DRAFT 3 November with pressure ridge addition.

Methane is a greenhouse gas more than 100 times more effective than carbon dioxide in the short term.  It is stored in the form of clathrates which are unstable if pressure is lower or temperature is higher than a line on a pressure versus temperature graph. Figure 1 shows that the slope of the atmospheric concentration has sharply increased since 2007.  Previous high levels of methane were associated with the Permian mass extinction, 250 million years ago.

Figure 1. Anomalies of CH4 mean volume mixing ratios for Northern and Southern hemispheres courtesy Leonid Yurganov.  Updated mixing ratios (Dlugokencky et al., 2009) were subtracted from the seasonal cycles averaged over 2003-2007. The right scale shows the anomaly of total mass of CH4 in the tropospheric layer of each hemisphere. The growth has been continuing in 2010-2011, according to the updated satellite data by Frankenberg et al. 2011.


This note discusses the design problems of a system to deploy kilometre-sized areas of plastic film to collect methane from suitable areas of the sea bed.  The gas can be flared off at sea to convert it to less damaging carbon dioxide or perhaps, if there are very high flow rates, recovered by a gas carrier and used ashore.

There seem to be solutions to what appeared initially to be an insoluble problem.



The difficulties

When John Nissen first raised the problem of Arctic methane my initial reaction was that capture at the sea bed would be impossible.  But trying to design for the impossible can be interesting.  It seemed a useful exercise to identify the reasons for impossibility. We can list difficulties as follows:

  1. Methane release at very low flow rates over too wide an area.
  2. Release at very high rates over a small area such as a well blow-out.
  3. Rough seas during deployment.
  4. The presence of obstructions such as wreckage, rock outcrops, munitions or steep slopes.
  5. Fast, variable-direction or unpredictable currents.
  6. Equipment sinking into very soft ooze on the seabed.
  7. Hydrogen sulphide toxicity.
  8. Unacceptable biological consequences due to the presence of equipment.
  9. The need to recover everything at some date in the future.
  10. The pressure ridges shown by Peter Wadhams at the Chiswick workshop.

I now believe that despite these problems methane can be captured in quite large quantities from areas of several square kilometres of plastic film in a single installation. 

The design

The film sheet is packed into a pair of left and right-handed rubber trough cases [1] and [2] with a rectangular inner section as shown in figure 2. Each trough case carries two steel cables [3].  The trough cases would be produced by a continuous moulding/extrusion machine in lengths of several kilometres using plant similar to that used for electrical cables. The left and right handed pair are connected at the centre by two thin isthmus strips of material [4] [5] above and below a rectangular section passage.  The passage contains a rectangular section runner [6] with two blades [7] [8] which can be pulled through the full length of the extrusion by a steel cable. [9].   If the steel cable is pulled the two blades will cut the connection strips and the trough case halves will be separated. 

The underside of the   trough case extrusion has a moulded tread with a pattern of saw-tooth section ridges [10] lying at an angle of about 30 degrees to the length of the extrusion. This ridge angle is an important design parameter.  At the outer corners of the bottom of the insides of the trough cases are recesses [11] into which a bead on the edge of an extruded plastic sheet can be pushed.  The outer walls of the trough are much thicker than the inner walls and contain galleries [12] along which methane can be transported to riser pipes. They connect to the higher points of the saw-tooth moulding. A high-density filler is added to the rubber to make sure that it is heavier than cold sea water but not heavier than the ooze on the sea bed. The outer edges of the extrusion [13] are sloped like the front of a sledge.

At the bottom of figure 2 the troughs are shown filled with a zig-zag stack of flexible plastic with a density just greater than cold sea water and a thickness of about 200 microns.  The zig-zag stacks on each side a joined at the top [14].  The lower edges with a bead are pushed into the recesses in each trough.  This plastic would be produced by a second extrusion machine consisting of interdigital plates to be described later.  If the width of each trough is one metre and the trough depth is 150 mm there will be space for 750 layers of zig-zag plastic, giving an extended width of 1.5 kilometres when the zig-zags on the two sides are unpacked.  The stacks of plastic film can be packed securely by lid flaps [15] retained by a vacuum maintained through pipes [16]. 

The length of plastic and rubber would be wound in a single scroll on the drum of a pipe-laying vessel such as the Stena Apache.  A drum diameter of 35 meters could take a width of 1.5 kilometres and length of 3 kilometres, giving a capture area of 4.5 square kilometres.

Figure 2. Empty and filled extruded rubber trough cases with 4 times enlarged views of end and centre. 

Deployment.

Survey vessels with side-scan sonar and methane detection sensors would look for suitable sites with no large obstructions, suitable current velocities and comfortable methane emission rates.

Small obstructions can be levelled with robotic sea bed vehicles such as the one described at the 2011 EWTEC conference.

The pipe-laying vessel would take station well downstream of the target area and pay out the scrolled material to the sea bed as if it were oil pipe.  The extreme flexibility of the trough case (relative to 12 inch steel pipe) would allow wave tolerant J-lay rather than an S-lay release.

Once the full length of the package is on the sea bed (figure 3) it would be towed along the seabed by ropes attached to the fore end of the rubber extrusions until it reached a point before the start of the target area equal to the string length divided by the cosine of the ridge angle.  If possible the tow direction should be perpendicular to current and swell.

The central cable with knife blades would be pulled through the rubber extrusion to separate the two troughs.

The vacuum retaining the lid flaps will be released.

Towing to increase the width of the film can now begin. Towing from the pipe-laying vessel would mean lifting the leading edge of the pack and there might be disturbance by waves.  It is preferable to use a horizontal force from a sea bed walking vehicle.  There might sometimes be an advantage in raising and lowering the leading edge in the way used for aligning carpets.  The tow force would depend on the weight of the package in water and the coefficient of friction to the sea bed. This is expected to be about 250 kN.  This will set the size of the steel cables embedded in the rubber extrusions which transmit the tow force along the length of the rubber and the bollard pull of the tow vehicles.

The tow vehicles will keep the tow lines pointing along the line of the package but the angled ridges would make the two troughs move apart from each other and so the tow vehicles will take diverging courses. The layers of plastic film will be pulled away from the zig-zag stack, as shown in figure 3, with the weight of the retaining lids providing a gentle resisting force.. GPS systems will be used to keep the advance rate of the tow vehicles matched.

The small density difference between plastic and sea water will mean that the drag friction between plastic and sea bed will be very low with a factor of safety of several hundred relative to the plastic strength.

The ridges in the rubber extrusion will leave furrows on the surface of the seabed.  When the furrows are covered by the plastic sheet they will form passages for the removal of gas through galleries in the outer walls of the trough.

The outward movement of the trough cases will build up material from the sea bed at the front of the outer sledge faces.  Water moving through eductor jets [17] can move some of the sea bed material over the film.

The gas pipe connection from below the film to the surface will bring its pressure closer to atmospheric.  Eventually several bars of water pressure will clamp the film and trough casings firmly to the sea bed.


Figure 3. Deployment of the film using the side force from the inclined ridges at the bottom
of the trough cases. Proportions are grossly distorted.


Tooling

Thermo-plastic films can be made by heating pellets of the feed stock to their melting point, pumping the liquid material through fine gaps in an extrusion tool and progressively cooling the downstream section of the tool to a temperature at which the film can be handled. The energy requirement is the sum of melting heat and pumping pressure.  Much of the heat can be recycled back to the incoming feed stock. The product is easier to handle if the pumping is in a downward direction.

The tool will consist of one inner and two outer stacks of plates each of which consists of two half plates which have been machined with a zig-zag coolant channel and then riveted and spot-welded back together as shown in figure 4.   The key problem is maintaining an accurate gap, probably 200 microns, between inner and outer plates.  Gravitational sag will be avoided if plates are vertical.  At the top of the tool where the film material is still liquid the gap can be defined by streamlined shims but in the cooler regions it must be actively controlled with no physical blockage.

Material from a rolling mill usually has quite large flatness errors and a skin under compression.  The first step will be stress relief by raising the plate temperature to 650 C for an hour and cooling it slowly.

Toolroom surface grinders can work to a flatness better than 3 microns but if curved parts are held flat on a magnetic chuck the curvature will be restored when the magnetic flux is removed.  It will be necessary to hold the plates on a hot wax chuck as used in the optical industry.  It might be useful to consider a low-force cutting technique such as spark erosion.

Figure 4.    A grossly distorted plan view of the topology of the extrusion tool with exploded parts. A 1500 metre width would require 750 plates rather than eight.  Maintaining a gap for the film thickness is a challenging problem but may be done with differential temperature control. The tool for a 1500 metre width of film would weigh about 200 tonnes.  If the differential temperature idea is not feasible, smaller tools could be used but a way to store and join kilometre lengths edge to edge would be needed. Temporary coiling looks difficult.



Gap control

We can use an array of capacitance transducers to measure the gap between plates of an assembled stack.  We can cover the surfaces of plates with resistive heating elements either side of the cooling channels.  By differential control of the heating currents we can control the local curvature of a plate.  The coefficient of thermal expansion of stainless steel is 17 part per million per C degree.  A temperature difference of 1C across a 15 mm plate will induce a radius of curvature of 440 metres.  If the width of the heating element is 100 mm this means a deflection of 11 microns.

A neat way to provide plate deflection control is to divide the plate surfaces into 100 mm squares with a resistive layer filling most of the area.  The squares would be connected in series and driven with a constant current from a high impedance source rather than a constant voltage.  The current would be diverted around the heating element by a parallel, high-frequency switch operated for a variable fraction of the time.  A small fraction of the surface with a grounded guard backing would be given a high-frequency excitation to measure the capacitance to the adjacent plate.

Cold heat exchanger fluid will be pumped into the bottom of the vertical tooling plates and emerge from the top at nearly the melting temperature of the plastic film.  After some extra heating the fluid will then move downwards through a vertical-tube heat-exchanger to melt the incoming plastic.

Solidified film coming out of the bottom of the tool will be further cooled by an upward flow air which will then be directed down through a bed of rising feed pellets and shredded plastic being recycled.  Air can flow easily through gaps between pellets or shredded feed stock.  The surface area of pellets is large even if heat transfer per unit area is low. Heat can flow more easily between liquids.  However there will be an awkward gap between solid but nearly molten pellets in the air in the pellet heat exchanger and liquid in the one above it.  Although the temperature difference might be quite small the amount of latent heat of fusion might be substantial. 

Gas flow rates

A slide (number 34) from the Shakova - Semiletov paper given at the November 30 2010 DoD workshop in Washington, gives a figure for methane flux of 44 grams per square metre a day over half a 500 metre transect, shown below.   This is well above other observations.   The calorific value of methane is 55 MJ per kilogram so this would be a thermal power of 28 MW per square kilometre.  These conditions might well not apply to the full film area and, at this rate, it would probably not be worth collecting methane on a ship.  In future the rate, and gas prices, might increase. However the power level should be enough to drive a mechanism with chain saws and heat transfer pipes to keep a clear hole for a flaring stack in a moving winter ice field if methane release in winter was thought to be a problem.  

Size of release plumes

This paper has described what I believe to be the largest possible collector area using present technology.  We need to know more about the size and spacing of release plumes to decide if the area has to be as large as this.  One example of the kind of data needed is given in figure 5.  

Figure 5. An echo sounder image giving the size of methane plumes from Shakhova et al.. This shows a transect of about 500 metres in the Laptev sea showing bubble plume return features
and also zooplankton other non-bubble scatterers such as fish.


Material quantities

The Shakhova presentation also mentioned total areas of methane hot spots of 210,000 square kilometres, the area of a square of side 460 kilometres.  The proposed design needs about 200 tonnes of plastic film per square kilometre. Total world consumption of plastics in 2010 was about 300 million tonnes and forecast to rise to 538 million in 2020.  Protecting the Shakova area with coverings which lasted 10 years would take about 1.5% of total present world plastic production.

Recovery

Maintenance would be very difficult and is not planned. But anyone putting anything into the sea has an ethical duty to plan for its recovery.  The proposal is to make structures of two cutting discs about 2 metres in diameter separated at 12 metres which can roll along the length of the film to cut it into 12 metre wide strips.  The ends of the cut can be gripped with a vacuum plate, lifted to the surface and wound round a drum.  The area of the long side of a 3 km length sheet of clean film is only 0.6 square metres.  Over a period of years it will probably have acquired biological growths, some of which can be removed by pulling it between contra-rotating brushes.  It is desirable that growth thickness can be reduced to the level at which film can be packed into 2.2 metre diameter for movement in a sea container.  For a film length of 3 kilometres this means a thickness of film plus growth of 1.25 mm.   The extruded rubber trough cases would be wound on the drum of a pipe-laying vessel.

Comments on the feasibility of this proposal, however critical, would be welcome.

Conclusions.

There is a wide range of estimates for the rates of methane release from Arctic seabeds but the higher ones are alarming enough for all defensive measures to be carefully examined.

Initial design work for the manufacture and deployment of kilometre-sized areas of plastic film to capture methane suggests that that this may be possible for a range of emission rates provided that the areas of the sea bed are clear of obstructions. This conclusion should be checked with people from the plastic and rubber industries.

Deployment and recovery will require pipe-laying vessels from the oil industry , such as the Stena Apache, and specialised seabed crawlers which have been designed for wave and tidal-stream installation.

Unless methane emission rates are even higher than suggested it will not be economical to recover methane for use on land and so flaring off at sea is more likely.  However there may be enough energy to drive ice-cutting equipment to keep the water round a flare stack clear of drifting ice in winter.

The extrusion tool for a 1500 metre width will require about 200 tonnes of very flat stainless steel sheet. The critical problem is maintaining an accurate gap in the extrusion tool.  This can be done with differential temperature control of opposite surfaces of a stack of interdigital plates with central cooling channels. 

The separation of halves of a film package can be done by the force generated from angled saw-tooth ridges on the underside when the package is dragged over the sea bed.  This allows very wide film coverage from an easily transported package and leaves tracks for methane flow.

If the underside of the film has a pipe connection to the atmosphere the pressure from water above it will clamp it firmly to the sea bed.

Work on long-term biological testing of candidate film materials should begin as soon as possible.

It is necessary to have credible techniques to recover all materials from the sea bed.  The proposed method must be critically checked by experienced offshore engineers.

A 4.5 square kilometre area of 200 micron sheet will need about 930 tonnes or 25 railway trucks of plastic but this is small compared with world production.  Energy consumption in the present plastics industry is about 10 MJ a kilogram compared with 2.25 MJ for the latent heat of steam.  If the film extrusion velocity is 10 mm a second we will need 3.5 days for one pack and a power of 35 MW.  Heat pump technology could give a very large reduction in energy consumption and must be carefully investigated.

We may have to avoid deployment in water depths less than the deepest pressure ridges. The leading ice authority, Peter Wadhams, says that these can reach down to 34 metres below the surface.

Actions

Resolve the three-order of magnitude dispute about methane release rates and investigate sea bed methane release rates and their variability in space and time.

Check design assumptions with the plastic film and rubber extrusion industry. 

Choose the best candidate film materials with density just greater than cold sea water (1028.4 kg/m3) and establish stress capability in working conditions.  A large strain length is more important than tensile strength.

Place specimens of the various film types in suitable test site in northern Norway and observe biological results especially recolonization rates.  The earlier this begins the better.  Albert Kallio has warned about anoxic conditions below the film.  The area of test film must be large enough to replicate this.

Measure tow forces on 5-metre sized blocks and establish the best ridge angle for a range of sea bed conditions from gravel to sand to ooze.

Place blocks of various shapes and densities fitted with accelerometers on the sea bed and measure how many roll or slide.

Carry out a sonar side-scan survey to identify obstructions in suitable areas.  Some, such as bullion cargoes, may be removable.

Collect information on depth and occurrence of pressure ridges in methane release areas.

Pray that the continual underestimation of the potential climate risks by people who are responsible for defending us against them does not continue.

Links

World plastic production

Shakhova PowerPoint presentation link.

Shakhova Semiletov paper


Pipe-laying vessels

Other collected papers

References

Dlugokencky, E. J., L. M. P. Bruhwiler, J. W. C. White, L. K. Emmons, P. C. Novelli, S. A. Montzka, K. A. Masarie, P. M. Lang, A. M. Crotwell, J. B. Miller and L. V. Gatti (2009), Observational constraints on recent increases in the atmospheric CH4 burden, Geophysical Research Letters, 36, L18803, 10.1029/2009GL039780.
Frankenberg, C., I. Aben, P. Bergamaschi, E. J. Dlugokencky, R. van Hees, S. Houweling, P. van der Meer, R. Snel P. Dol (2011), Global column-averaged methane mixing ratios from 2003 to 2009 as derived from SCIAMACHY: Trends and variability, Journal of Geophysical Research-Atmospheres, 116(D04302), 1-12, 10.1029/2010JD014849.
Montzka, S. A., E. J. Dlugokencky and J. H. Butler (2011), Non-CO2 greenhouse gases and climate change, NATURE, 476, 43-50, 10.1038/nature10322.