Clathrates and climate change

Definition

A clathrate is a chemically constructed lattice structure in which one type of molecule traps and contains another type of molecule without forming a chemical bond. Clathrates may also be called gas hydrates (sometimes using the name of the gas, such as “methane clathrate”), host-guest complexes, or molecular compounds. They are sometimes referred to as “marsh gas.”

The most common types of clathrates are those involving water trapping a gas, such as methane, ethane, propane, isobutane, butane, nitrogen, carbon dioxide (CO₂), or hydrogen sulfide. Methane trapped in water is the most common type of naturally occurring clathrate. Methane clathrates usually occur when organic matter in a low-oxygen environment is degraded by bacteria. This situation usually occurs under ice sheets in the ocean; usually, these structures are found in sediments. A clump of methane hydrate looks like a snowball, but at room temperature, the ball dissolves. It can even be lit on fire, as the methane inside the lattice structure burns.

Significance for Climate Change

Because methane is one of the greenhouse gases (GHGs), gases that trap warmth on Earth’s surface, the release of large amounts of methane could cause the Earth to become warmer. In the geologic past, sudden releases of large amounts of methane may have triggered abrupt climatic events. Geologists believe that about 635 million years ago, a large quantity of methane was released into the atmosphere from ice sheets that covered Earth. This release caused an abrupt global warming, taking Earth from a cold, relatively stable climate to a very warm, still relatively stable climate. Scientists think this event quickly warmed the Earth by tens of degrees Celsius.

Sudden releases of methane could occur if either the temperature rises or the pressure falls on the sediment above the methane clathrate structure. Often, sediment continues to accumulate over the methane clathrate until the weight of the sediment causes the clathrate structure to become unstable, when it disintegrates into water and gas. The covering sediments then become unstable and release methane into the atmosphere. The methane reacts with oxygen to form CO₂, which can kill any animals that need oxygen.

The US Geological Survey estimates that up to 8.5 million cubic kilometers of methane clathrate exist in the seafloor worldwide, more than in all other fossil energy resources combined, so methane clathrates are being investigated as a potential source of natural gas energy. However, getting to this energy source is dangerous, as the accidental release of methane into the atmosphere could be deadly in and of itself. In addition, a release of this sort could affect the global temperature or even cause tsunamis if landslides under the ocean were triggered. Safe methods of harvesting this resource would need to be developed, as methane can be very explosive. Deadly methane explosions have occurred in mines in Harlan County, Kentucky, in 2006, in Ulyanovskaya, Russia, in 2007, in Vorkuta, Komi Republic, Russia, in 2016, in Karaganda, Kazakhstan, in 2023, and in Tehran, Iran, in 2024. A deadly house explosion occurred because of methane in Oak Grove, Alabama, in 2024 because the structure was over a mine. Methane can also cause an “exploding lake,” such as Lake Kivu in Africa. There, the lake water interacts with volcanic gases to produce methane and CO₂, which are potentially deadly when released.

Harvesting methane from under ice sheets for fuel requires two different approaches, both of which are potentially dangerous. With the depressurization method, holes are drilled into a layer of methane hydrate just under the ice, which releases pressure and causes the methane to flow up a pipe. This approach uses less energy than the other approach, that of thermal injection. Thermal injection involves pumping hot water into a deposit of methane, which destabilizes the structure of the methane clathrate. A promising future approach involves injecting CO₂ into the hydrate formation, displacing the methane in the structure.

Bibliography

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