What is a Clathrate?
A clathrate is a compound which is caged or enclosed. One of the components of a clathrate is a crystalline open structure in which the other component’s molecules or atoms can fit and get trapped. The component which has an open structure is called the host, while the component which gets trapped is called the guest. Therefore, clathrates share a host-guest relationship. (Vaidya, 2004). The figure below shows the structure of a clathrate [See Figure 1].
Methane Hydrates, which belong to the group of clathrates, are white solids just like ice. In methane hydrates, methane molecules are trapped in cages of water. The microorganisms that live in the deep sediment layers produce methane by converting the organic substances slowly into methane. These organic substances are the dead plankton that lived long ago, sank and finally merged into sediments. The stability of methane hydrates depends on low temperatures and pressures greater than 35 bars, therefore making the seabed a perfect location for their formation. The following figure [See Figure 2] summarizes the locations of methane hydrates and consumption of methane (written in red).
How do they contribute to climate change?
The positive methane feedback loop explains how methane contributes to climate change. Basically, methane is a potent greenhouse gas. Methane and other greenhouse gases such as carbon dioxide increase the atmospheric temperature and result in global warming. This results in the melting of glaciers, sea level rising, and oceans and permafrost getting warmer. When the ocean water gets warmer and permafrost begins to melt, the methane hydrates get instable and begin to melt. In response to this, methane gas is released which again adds up to the warming, and so the cycle continues. The figure below shows the positive feedback loop of methane hydrate [See Figure 3].
As compared to the carbon that is released annually due to fossil fuel burning, carbon in the form of methane hydrates is approximately 100 to 500 times greater, which makes it almost 1000 to 5000 giga tonnes [See Figure 4].
Methane hydrates are stable at low temperatures, but as soon as temperature gets higher, they break down. Methane is not directly released from the ocean surface, but it is oxidized into carbon dioxide, which itself is a greenhouse gas. Therefore, methane hydrates have become quite important in relation to climate change. Moreover, carbon dioxide not only adds up to global warming, but it also contributes to the acidification of oceans and it reduces the amount of oxygen in the oceans.
Moreover, if we look at geological records, we can see that in the past, breakdown of methane hydrates has significantly contributed to the extreme global warming and massive extinctions of the aquatic life.
How do they play a role of potential energy source?
Even though, methane hydrates are harmful for the environment and can adversely affect the climate, but they can also play a role of potential energy source. From centuries, people have been using coal, oil and natural gas as an energy source. The amount of methane (component of natural gas) in methane hydrates is far greater than the conventional sources of natural gas. The mining of methane hydrates is a costly operation, but efforts are being made regarding this. Since other energy sources are getting expensive, methane mining is attracting the offshore industries. It is estimated by various scientists that methane mining could be a feasible option in terms of cost at the rate of 50-60 US Dollars per barrel.
Methane hydrates are a representation of a natural gas reservoir which has not yet been tapped or we can say exploited. This could be a great energy source if mined properly. According to British Broadcasting Corporation, methane hydrate has been a controversial source of energy as it has been referred to as a ‘dirty fuel’ at places and somewhere it has been mentioned as an energy savior. The figure (see figure 5) below shows a methane hydrate as an energy source.