The real problem with Methane Hydrates is Sliding under the Radar

There has certainly been a lot of discussion lately about methane hydrates. You may have missed it unless you, like most concerned about global peak oil and peak energy, specifically search and listen for it. Most of that discussion, quite understandably in our energy-addicted world, has centered on the potential of using these vast reserves of methane as a fuel source. Methane hydrates, after all, contain more carbon energy than all of the world's oil, natural gas and coal combined.

Those estimates, like hot air, are, in fact, expanding all the time. Some estimates suggest methane hydrates may contain 3-4 times the carbon energy of all global fossil fuels combined.

For those not familiar, methane hydrates are molecules of methane gas (the basic constituent of natural gas) locked in a cage of water ice.





They exist in two places throughout the world. Marine methane hydrates exist on most of the world's continental margins, particularly along the subduction zone of tectonic plates such as along the west coast of North America. Methane hydrates also occur in land-based and sub-sea frozen permafrost in Alaska, Northern Canada, Russian Siberia, far northern Europe, and in small deposits in Antarctica.




The sheer volume of methane hydrates and their occurrence on shore in permafrost and near offshore on continental margins do make them an attractive prospect as a future, accessible, post-oil energy source. There has been far more research into the potential exploitation of methane hydrates than was ever the case for oil, natural gas or coal. The requisite geology and, now, the location of these deposits are well known. All that stands in the way of exploiting this vast energy resource - from the point of view of energy executives, economists and politicians - is the extraction technology, the global distribution technology and network, the economic evaluation and the financing to build the massive infrastructure that would be needed to effectively and efficiently exploit it fully. No problem! It may, in fact, still be several decades - in a business as usual climate - before all of these factors can be dealt with and methane from hydrates can be exploited commercially.



There are, of course, other points of view. Paleoclimatologists are increasingly convinced that massive and surprisingly sudden releases of submarine methane hydrates have been responsible for periodic and disastrous rapid rises of global temperature, largely resulting in the quick - in geologic terms - end of past ice ages. The study of deep ice cores from Greenland and Antarctica, the study of areas of ocean floor zones of extensive pock marks and growing evidence of current increasing methane releases from melting permafrost and the Arctic Ocean floor all strongly lend credence to this hypothesis.



All of that, of course, makes methane hydrates and their possible release as a gas into the atmosphere a serious concern, in this period of increasing concern about global warming, from an environmental point of view. Methane in the short term, you see, is 62 times more potent as a greenhouse gas than carbon dioxide. Over ten to twenty years time as it oxidizes in the atmosphere it weakens to just 20 times the potency as a GHG compared to carbon dioxide. After about ten years atmospheric methane completely oxidizes. But that isn't the end. It oxidizes into carbon dioxide and remains a greenhouse for another century.

Another, and perhaps the least understood and certainly the least discussed, point of view about methane hydrates involves physics. The physical nature of methane hydrates and the quite distinct physical properties of water - specifically H2O - and of methane (CH4) independently function both as a barrier to exploitation and as a serious environmental risk in conjunction with global warming.

Submarine methane hydrates primarily occur in what has been called the Hydrate Stability Zone. This is a relatively narrow zone where the combination of water temperature and water pressure are suitable for the formation and, more important, the stability of methane hydrates. In general, at present, this is 300 to 500 meters below the ocean surface but varies and is very specific in different locations depending on water temperature. The geology of the area is also a very important factor; whether the bottom is sandstone, other stone, coarse silt or fine silt. All of these variables affect the ability to form methane hydrates and the way those hydrates will be distributed in that medium.

All methane hydrates, you may have guessed from the above, are not created equal. The water ice that forms the hydrate cage and the methane gas in that cage are both essentially consistent but the manner in which they combine to form the hydrate varies considerably. And so does the volatility and stability of those deposits.

I will not go into a great detailed discussion of those differences. I will limit it to a couple of key factors.

Water - more specifically H2O which is only water above 0C and becomes vapour at higher temperatures - reaches its maximum density of 999.9720 kilograms per cubic meter at a temperature of 3.98C. At the freezing temperature of 0C its density has reduced to 998.8395 kilograms per cubic meter, 988.1170 at -10C. The critical part of that range, with regard to methane hydrates, is that from 0C to 3.98C. That is where we will focus.

The lower density of H2O as ice (998.8395) at 0C (even lower if the ice is super cooled) is what allows ice to float on the surface of water. Average global ocean temperatures today (this has varied over geological time, especially during different eras of ice age and global warming) is 2C. At 2C H2O has a density 999.9400 between that of ice at 0C of 998.8395 and the maximum density at 3.98C of 999.9720. It still supports, therefore, the lighter ice even in the Arctic.

Anyone in a northern climate is familiar with spring thaw. As the water below ice warms in the spring it first expands, pushing up and cracking the ice, until it reaches its maximum density at 3.98C of 999.9720. Above that temperature the water begins to shrink (will reach a density of 999.7026 at 10C) as the temperature rises, leaving a gap of air between the ice and the water below. The ice can, as most young boys in northern rural areas can attest, be left high and dry and collapse under the weight of a person walking on it.

Because of the lower density (greater buoyancy) of ice relative to sea water, submarine methane hydrates are always under pressure, physically wanting to rise to the surface. The deposits only become "relatively" stable when anchored by sufficient sediment on the ocean bottom. When and if that "anchorage" breaks down or is swept away, for example, by a sub-surface landslide, the hydrates can suddenly be released into the water and rise toward the surface.

Now the other side of the problem. At 1 atmosphere, methane is a liquid below a temperature of -182.5C. There is no known naturally occurring liquid methane on earth. Above that temperature methane is a gas. Its density constantly diminishes as the temperature/pressure gradient rises. To my knowledge, which is incomplete, scientists have not really answered the question of why the methane trapped in hydrates is stable in that form. The density of the gaseous methane in hydrates is 162 times greater than methane gas in the atmosphere. At the temperature and pressure of the sea water around and above the hydrate deposits, the methane gas contained in the hydrates should have much lower density (occupy much more space) than it does. This physical anomaly means that the pressure on the methane gas to expand is constantly at odds with and pushing against the ice cage enclosing it. This is a key component of the essential instability of methane hydrates.

Gas density generally decreases far more rapidly for gases than liquids or solids as temperature rises or pressure decreases. That means two factors can affect the stability of methane hydrates currently in the hydrate stability zone. Changes in sea level can affect the water pressure in the zone: a drop in sea level can decrease the pressure. Changes in temperature of the water can have the same effect. Increase of the temperature above the current average 2C can also dramatically affect that stability.

Global warming, ironically, fortunately means we are in an era of rising sea levels, not lowering sea levels. The pressure that pushes down on and stabilizes methane hydrate deposits in the oceans is, therefore, increasing, not decreasing. Global warming, however, also means that water temperatures, as well as atmosphere temperatures, are on the rise.

Much of the debate around global warming centers on whether we are heading for a global temperature increase of 2C, 4C or higher. On the surface these seem like such small numbers to be the center of such passionate debate. But the critical temperature spread we are dealing with is between 2C (the current average global ocean temperature) and 3.98C (the temperature at which H2O reaches its maximum density (it will shrink, lowering sea level and decreasing oceanic water pressure between those two temperatures) and begins to decrease in density: begins to expand again). That is a temperature differential of just 1.98C.

As the ocean temperature rises it doesn't matter what the specific temperature in the local hydrate stability zone currently is because that zone is a product of both temperature and pressure. In the Barkley Canyon off the coast of Vancouver Island, for example, the hydrate stability zone is at a depth of 850 meters, much deeper than the normal hydrate stability zone of 300m to 500m depth in other locations. As the temperature in the hydrate stability zone rises at whatever depth it occurs, however, the stability of the hydrates will diminish.

The individual physical characters of the water ice that makes up the hydrate cage and the methane gas trapped inside accelerate this instability. As the temperature rises (generally from 2C to 3.98C) the ice forming the hydrate cage shrinks as it is influence by the temperature of the surrounding water and begins to soften as the physical bonds holding the ice in a stable structure weaken. This shrinking puts further pressure on the methane gas inside, increasing its density. But the methane gas inside that cage is already 162 times the density it is at 1 atmosphere and is under considerable pressure to expand. As the temperature rises in the hydrate stability zone and the ice cage weakens and the methane gas's pressure to expand increases, the stability of the hydrate diminishes rapidly. The upward pressure on the hydrate ice, which wants to float up to the surface (the methane gas trapped inside is also more buoyant than the ice or the surrounding water), also increases as the temperature rises.

To my knowledge no scientific studies have yet been conducted that pinpoint exactly where on the temperature/pressure gradient the water ice cage of the hydrate ruptures and releases the methane gas into the surrounding environment. There is mounting evidence that the number of subsea methane vents in the Arctic, which is generally warming faster than other oceans, is increasing, as is the volume of methane gas issuing from those vents. This suggests that, in the Arctic at least (which holds the highest concentrations of methane hydrates of all the oceans), the temperature rise is already compromising methane hydrate stability.

In areas of fine sea bottom sediment, which is the case in the majority of methane hydrate deposits, the methane hydrates form stratified seams. Proceeding downward, each seam acts as a "cementing" cap, holding hydrate seams and free methane below in place. The disassociation or breakdown of hydrates as the ocean temperature increases will proceed from the top of the hydrate deposit downward. In these seamed, soft-sediment deposits that means that the top seam, which functions as a cap on all the methane and hydrates below, will break down first. It's ability to function as a cap disappears and the risk of a rapid, potentially massive release of methane increases dramatically.

The same sort of results that can occur naturally through warming of the waters around the methane hydrate deposit can also occur if the submarine methane hydrate deposits are destabilized by human activity. Any attempts to drill into methane hydrate deposits, whether exploratory or commercially for energy production, can break down the stability of the hydrates, particularly in association with rising temperatures, either in the surrounding sea water or from the drilling itself (the favourite intended method of extraction is to inject hot water into the hydrate deposits).

The current discussion and debate surrounding the intended exploitation of methane hydrate deposits involves energy experts, various types of scientific experts, and anxious, eager governments. If that is where it stays I am not very confident that scientific reason and caution will win out. The general public, including you, must put methane hydrates on their radar and be prepared to hold accountable those pushing for methane hydrate exploitation. Public pressure must become a key element of making sure that we do not rush into over-exuberant and overly-optimistic exploitation of this resource, to the detriment of mankind, other living species and the planet itself.

AUTHOR'S NOTE:
Hundreds of articles, papers and web sites were researched as part of writing this article. I have not listed them here as the list would be far too long. If anyone is interested in those references and links, however, they can contact me by e-mail and I will gladly supply them. My e-mail address is; richard.embleton@sympatico.ca

Also see my other Methane Hydrate articles in this blog;

Methane Hydrates: What are they thinking?
http://oilbeseeingyou.blogspot.com/2008/12/methane-hydrates-what-are-they-thinking.html

Methane hydrates: the next great energy source?
http://oilbeseeingyou.blogspot.com/2006/12/methane-hydrates-next-great-energy.html

Invest, invest, invest! Consume, consume, consume! No! No! No!

The first time it got really blatant for me was in September, 2001. That was when George Bush stood atop a demolished fire truck at ground zero and implored New Yorkers to go shopping and spend their money to restart the New York economy.

In our world maniacally driven by economics and money, the generally perceived solution to any problem has become spend, spend, spend. You can solve any problem by throwing money at it. The necessary assumption that is always demanded is that the future for which we are investing is limitless. Limitless growth. Limitless population. Limitless resources. Limitless oil.

If the economy softens it's because people aren't going to the mall and wasting their money on plastic trinkets from Shanghai. When they go to the supermarket they aren't picking up that cut of spring lamb flown in from New Zealand or those oranges flown in from South Africa. They aren't buying a new car every model year, for heaven's sake.

And when it comes to tightening in the oil market, we don't have a supply problem. We have an investment problem. The oil companies - especially those dastardly national oil companies that now control the bulk of the world's oil resources like Saudi Aramco, Pemex, Petrolios di Venezuela and Petrobras - are not investing enough in bringing new oil to market. The oil exploration companies are not invest enough in new exploration for increasingly illusive deposits of oil. Oil companies are not investing enough in new refineries. Not enough is being invested in new bulk oil carriers to move that oil from increasingly remote sources to increasingly thirsty markets.

Politicians dream of - and expect oil company execs to do the same - vast resources of untapped oil out there someplace if only the oil companies and exploration companies and shipping lines and pipeline builders would all get off their wallets and invest, invest, invest.

But those to whom those governments and politicians turn for the fuzzy statistics that support their limitless belief in limitless growth and limitless resources are increasingly injecting sanity, not money, into their efforts. Fatih Birol, chief economist to the International Energy Agency (IEA), is the latest to opt for rational sanity rather than unquestioning faith. Perhaps he is tiring of being mistakenly identified as Faith Birol.

In a stunning departure from the IEA norm he has conceded, in an interview with George Monbiot of the Guardian, that we are headed for global peak oil by 2020, just eleven years away. Personally, I believe that is still a little far out. But that happens to most people as they come to grips with peak oil. They cling to the most optimistic estimates, the ones furthest out in the future. Over time, as they re-examine the foundations of the limitless faith without the benefit of their rose-coloured glasses, they gradually accept that the peak will be - for geologic, geopolitical and economic reasons - much sooner rather than later. I have become comfortable with the appearance that we passed peak in the spring of 2005 and have been bumping along on the gradual down-trend of the peak oil plateau.

Geology is the ultimate constraint that defines peak oil. Eventually it becomes abundantly clear that we simply cannot find enough new oil to offset the escalating declines in existing oil fields. But peak availability will, and even now is, ultimately negatively impacted by other above ground factors.

Back to where we began, investment. As an industry matures the stewards of that industry increasingly and more obsessively look ahead. They are trying to determine at what point it is unwise to continue investing because the life expectancy of their enterprise has shortened to the point that further investment cannot be recouped. Quite simply, you get no return from your investment when growth stops. That is what the stewards are trying to identify as they look ahead, the point at which growth will stop and their enterprise will go into decline.

Banks are no longer willing to invest in sub-prime mortgages because they can no longer see increasing real estate prices in the future. They see a future in which housing prices - read equity - will decline faster than the "homeowner" can pay down their mortgage. No growth, no equity. Real estate ceases being an asset and becomes a liability.

Oil companies and exploration companies have for years been experiencing lower and lower returns on their investment. Exploration investment continued to increase for years while the discoveries of new oil deposits - the return on their investment - continued to decline. In fact global oil discoveries actually peaked in the sixties, over four decades ago.

That was acceptable for a long time, if you continued to have faith that the big discoveries were still out there and all you had to do was find them. But what happens when reality bites? When you lose the faith? When you realize that the big discoveries you keep throwing money into finding simply are not there to be found?

Oil companies, whether independent or nationalized, seem to have come to that point. Unused oil rigs are rusting in junk yards. Exploration rigs are abandoned if they are not being taken up for exploration for those middle east nations still willing to pour money into looking for new oil deposits. Reluctance grows to invest in pipelines to bring oil from increasingly remote and smaller fields to ocean oil terminals.

As long as credit is available people as individuals seem to be willing to spend money they do not have and may not have in the future. That willingness has built America as the world's greatest consumer nation. It has also made America the world's most indebted nation, and a nation increasingly unlikely to ever be able to discharge its massive global debt. Only now that credit is no longer available are they beginning to trim back. They are suddenly, one at a time, sitting at kitchen table looking at the pile of bills and asking themselves, "How the hell am I ever going to pay all of this?"

Corporations cannot afford themselves the freedom to wantonly spend themselves into unmanageable debt. That does not mean that their debt cannot become unmanageable. It can and definitely does as the economic environment in which they operate changes abruptly, outside of their control. That is the point at which corporations hail a cab, trundle on over to Pennsylvania Avenue and hang about on the steps of congress, cap in hand.

But the money that is magnanimously place in their proffered cap by congress is not going into new business development, not going to discharge debt. It is going into the coffers in a vain attempt to stay afloat, to survive. It is a lifeline.

As oil company executives pour over their charts and graphs detailing the company's projected future, they are increasingly willing to see the truth in those charts. The days of growth in oil deposits, in development, in profits, is rapidly coming to an end. The reality is that most of their growth in recent decades has been a result of merger and acquisition, in purchased reserves, not in newly discovered fields. It is the illusion of growth in a reality of decline.

Governments continue to chant: "Invest! Invest! Invest!" So far they have not heard, or have chosen to ignore the response: "No! No! No! There is nothing to invest in!" The oil companies are increasingly investing in buying back shares, artificially inflating dividends, as they prepare for their foreseeable demise. They are increasingly investing their money in wind, solar, geothermal and other alternatives as they prepare for the end of economically recoverable oil. They have been sucked into heavily investing in new exploration before, in the seventies and eighties after the peak in global discovery, only to see the price of crude fall through the floor.

Oil companies have access to far better data than we in the peak oil community have. We can see what is coming, and how quickly. That fuzzy view that we have is crystal clear to them. We can see the cloud of dust coming down the road. With their magnified clarity of vision they can see, in the midst of the dust, the four horsemen of the apocalypse confidently and arrogantly galloping toward them.

Methane Hydrates: What are they thinking?

The world's governments are beginning to come to grips with the reality that crude oil is a finite resource. That forces them to face another reality. The amount of that resource available for running global human society is about to go into terminal decline. We are at or soon to arrive at peak oil. Many analysts believe, based on the data, that we hit that peak in the spring of 2005. Other more optimistic analysts believe that peak may still be as much as thirty years in the future. Even that (I am not conceding that projection. I am in the spring 2005 camp.) is close enough that the majority of people alive today will have to begin to adjust to declining global oil production in their lifetime.

Optimists point to the fact that we have moved beyond various energy sources, on which the entire society depends, many times in the past. We have always found a new, better energy source to replace them. Even since the beginning of the industrial revolution we have moved through water power, steam power, coal, natural gas, electricity, oil and nuclear. Oil, however, has been the most important and workable energy source that we have ever discovered and exploited.

Where do we go from oil? What will be the next, better energy source that can power human society. There are many who see electricity playing an increasingly important role, including driving transportation. To many that electric future will be increasingly centered on a nuclear energy renaissance. On the fringes they see electricity generation from wind, solar, geothermal, tidal, hydro, wave and a variety of other options.

But oil is used for much more than powering the family car. I have trouble visualizing electric planes and electric ships. Hell, most electric cars have a battery range of under 100 kilometers. And I don't think you can make plastics from electricity. Last I noticed it required hydrocarbons.

In one form or another, in fact, hydrocarbons have been the world's primary energy source since the beginning of the Industrial Revolution over 200 years ago. It answers one extremely important need; portability. Hydrocarbon fuels, especially oil and its derivatives, can be easily move from one place to another. They can also be used on board to generate the power used to move it.

What is the next energy source that will give us what oil, coal and natural gas give us today? You may be surprised to hear that it may be the other hydrocarbon fuel. A Great many scientists, industry leaders and governments throughout the developed world believe that will be methane. More specifically they believe it will be methane hydrates.

Methane hydrates (also called clathrates) are bubbles of methane gas trapped in a cage of ice crystals. Methane hydrate deposits occur in locations all over the world. The most concentrated deposits occur under the Arctic Ocean, under the ocean floor on most continental shelves, in locations like the Gulf of Mexico, the Bermuda Triangle, the Dragon's Triangle south of Japan, and in permafrost surrounding the Arctic ocean. It is reliably estimated that the amount of methane trapped as hydrates globally exceeds by many times the total combined oil, coal and natural gas reserves that have ever existed on earth.

A chunk of methane ice exposed to the air and ignited will burn until all of the methane in that ice has been consumed. Methane hydrates, however, require specific conditions of temperature and pressure to keep them contained within their ice cage. Reduce the pressure - for example, by reducing the sea level and the pressure of water above the deposit - or increased the temperature and the methane hydrate deposit becomes unstable and begins to release the trapped methane into the atmosphere.

That is a problem. Methane is a greenhouse gas. In fact, it is 21-23 times more powerful as a greenhouse gas than carbon dioxide. When the methane trapped in the hydrate is released it expands by about 170 times.[1] Methane is lighter than CO2, lighter than air. As a result it rises rapidly through the atmosphere up to the lower-density stratosphere. On the positive side methane remains in the atmosphere for only about 10-20 years. CO2 remains in the atmosphere for over 100 years.

Scientists studying global warming have long been seriously concerned about the possibility of large scale methane hydrate destabilization and methane release into the atmosphere. The greatest concern is about the large volumes of methane hydrates under the Arctic sea floor and that trapped in the vast permafrost zone surrounding the Arctic Ocean. That concern has now been heightened by recent discoveries of hundreds of methane plumes on the floor of the Arctic Ocean north of Norway and Siberia. [2] There is also evidence in pock-marked sea floors of large releases of methane plumes in the geological past. [3]

Paleoclimatologists now believe that large scale, natural methane hydrate releases have been partly but significantly responsible for short-cycle global warming and global cooling cycles in the past. The recent discoveries in the Arctic, in fact, are thought to suggest that methane releases have contributed to the global warming that has occurred since the last ice age 15,000 years ago. [2]

The problem is that these methane releases have a strong positive feedback loop. As they increase the warming of the atmosphere that warming in turn increases methane release which in turn increases warming which in turn releases more...... You get the picture. Acceleration of global warming through this positive feedback loop, by increased methane concentration in the atmosphere, far more than CO2 concentrations, represents, to paleoclimatologists, a far greater risk of pushing us into the Venus effect, runaway global warming.

When it comes to satisfying the world's energy lust, however, caution may be thrown to the wind. Powering down human society is never an option put on the table when politicians and other leaders discuss energy policies and strategies. We have proven over and over again that business as usual is the only model that will be considered. How else can we explain the tar sands, oil shale development, deepwater oil extraction, coal mines extending out under the sea floor, and more?

There are various technologies under consideration for extracting methane from hydrate deposits. Most involve some form of heating the hydrate deposits - one, probably the dumbest and most dangerous, even goes so far as to suggest using nuclear explosions beneath the deposit to heat it, also suggested by some as a means of releasing oil from tar sands and oil shale - causing them to release the methane which is then collected and piped to a processing facility of holding tank. Proponents of methane hydrate exploitation, conscious of environmental concerns, are quick to offer reassurances like ".....tapping into the gas hydrates assessed in the study is not expected to affect global warming, said Brenda Pierce, coordinator for the USGS Energy Resources Program." [4] The louder and more frequent such reassurances are, of course, the more it suggests they are trying to cover up the probability that the result will be the opposite.

There are many projects underway, funded by governments throughout the world (Japan, India, China, South Korea, Russia, Norway, Canada, the U.S.), aimed at developing commercially viable technologies for exploiting the planet's vast methane hydrate deposits. The selection of sites for these projects are, themselves, a clear indication of one of the primary roadblocks to using methane hydrates as a societal-supporting energy source. They have sought out test sites with high methane hydrate concentrations.

Most hydrate deposits are too small or too dispersed to be commercially exploited. Also, unlike oil and natural gas, those deposits are generally not capped in such a way that the geology can be used to contain releases. Most of those deposits on the sea floor, in fact, exist in unconsolidated, sandy or silt sediment. The geology surrounding them is inherently unstable, difficult to contain. Once the deposit, or any large portion of it, is destabilized it is very difficult to prevent unintended, uncontrolled methane releases into the atmosphere.

Okay. I very begrudgingly accept that our leaders are not going to consider powering down as a potential tactic in the face of our impending energy crisis. Sooner or later the human race is going to have to accept that reality but clearly society is not prepared to accept it now. But methane hydrates are not like the other fossil fuels. And our approach to exploiting them is going to have to be very different. The risk to the climate and the environment is so much greater than has ever been the case with other fossil fuels. Most importantly, methane hydrates are globally affected by exactly the same constrains; temperature and pressure.

Global warming itself - it doesn't matter whether it is naturally occurring or caused by human combustion of fossil fuels - is the greatest threat of tipping methane releases into a runaway warming mechanism. Scientists do not know with any certainty yet how much of a global temperature rise is necessary to reach the tipping point where methane hydrate release into the atmosphere accelerates out of control. They do know that once that happens the acceleration will be self-sustaining and self-accelerating.

If our leaders take the same cavalier approach with scientific warnings about runaway methane release that they have taken with warnings about CO2 buildup in the atmosphere, and the long-term, safe storage of spent nuclear fuel, we are headed toward a much more serious atmospheric and climatic disaster than global warming experts have thus far suggested. Methane releases from the ocean floors and from Arctic permafrost have not been built into any of the current global warming models as a factor, including those models supporting the IPCC reports. Considering that methane hydrate deposits exceed the total of all other fossil fuels by magnitudes and that methane is more than 20 times more powerful as a greenhouse gas than CO2, that should be extremely worrying to anyone who accepts the validity of the global warming theory.

Other material;

1) Starting A Runaway Global Warming Process
2) Hundreds of methane 'plumes' discovered
3) A large methane plume east of Bear Island (Barents Sea): implications for the marine methane cycle
4) Study: Tap natural gas from Alaska's frozen areas