Most fossil fuels that humans burn come from deep reservoirs of oil, or coal mines on land. But a risky, potentially disastrous new technology could mean that a huge new source of greenhouse gases could come from the ocean floor. And new research suggests that submarine earthquakes are already paving the way to carbon emissions we didn’t even know were happening.
Methane is a potent carbon-based greenhouse gas that is emitted from decaying organic matter (i.e. landfills, cow digestion, and melting permafrost). The natural gas industry has been harvesting methane buried deep underground for decades to supply their product, despite persistent climate and safety concerns. Yet there’s an even more dangerous collection of methane hidden at the bottom of the sea. Though it’s somewhat easy to forget about it, a potentially enormous source of carbon pollution: methane hydrate.
Fossil fuel companies have not forgotten and they are extremely interested in finding an economical way to extract it from the sea floor. The reason is that the latest estimates put the amount of methane hydrate at 700,000 trillion cubic feet, or more energy than all oil and gas that has ever been discovered. It’s extremely hard to extract, and all known methods are very risky.
Also known as methane clathrate, or “fire ice,” methane hydrate is created when decaying organic matter under the ocean floor emits methane. This seeps up and mixes with seawater at the bottom of the ocean. It forms a cement-like icy compound within and on top of the ocean sediment, which actually stops more methane from seeping into the ocean. If the water above it gets warmer, some of the methane hydrate melts as methane, which bubbles up through the water column. In shallow water, it bubbles straight to the atmosphere but in deeper waters, the methane bubbles bond with the dissolved oxygen and water, creating carbon dioxide which bubbles to the surface, or stays in the water and makes the already-acidifying ocean more acidic.
But new research suggests that slow melting is not the only fate of methane hydrate. A study published in Nature Geoscience on Sunday found that undersea earthquakes could speed up this process. The researchers suggested that seismic activity fractures the seafloor, causing the methane below the surface to bubble up and get trapped within methane hydrates and sediment on the ocean floor. An earthquake could also cause methane to percolate through the water, either oxidizing in shallow water or escaping the ocean as methane emissions.
There are roughly ten magnitude seven submarine earthquakes per year. The authors of the study say that this could affect greenhouse gas emission calculations: “We therefore suggest that hydrocarbon seepage triggered by earthquakes needs to be considered in local and global carbon budgets at active continental margins.”
But why rely on chancy natural seismic activity to leak methane out of hydrates and reservoirs, when an artificial solution could soon be available?
Earlier this year, Japanese researchers successfully tested a new process that extracted methane hydrate from the ocean floor for the first time. The director of Japan’s Agency for Natural Resources compared this to the way shale gas was viewed a decade ago — too expensive for commercialization — but concluded “now it’s commercialized.” This process does have similarities to fracking, but instead of pumping fracking fluid into the earth and exploding the rock, it drills down to the seabed, relieves pressure on the hydrates, and dissolves the crystals into gas and water for collection.
However, harvesting methane hydrates poses the same risks faced by offshore oil drillers — pressure, drilling at depth, and the catastrophic ramifications of failure. If the drilling causes an underwater landslide, the methane could erupt to the surface all at once, a scenario called the “methane gun hypothesis.” This could release massive amounts of methane into the atmosphere, dealing a serious blow to cutting carbon emissions.
ConocoPhillips tried a process that was more like fracking last year on Alaska’s North Slope, which also has methane hydrates in the permafrost. They injected carbon dioxide and nitrogen into the hydrates and got natural gas to flow back out. However, the company said that “at present, the technology does not exist to produce natural gas economically from hydrates.”