Methane levels in the world have risen sharply by about 25 teragrams per year since 2006. That equals a global emission of 15 billion tonnes per year. The exponential rise has caused the atmosphere to contain two-and-a-half times the amount of methane than it did before the industrial revolution.
Methane might be of less climatic importance as compared to Carbon dioxide (CO2) as it is less abundant than CO2 and stays in the air for a period of only 10 years, however its molecule for molecule warming effect (calculated over 100 years) is 25 times higher. In simpler terms methane is capable trapping of 86 times the amount of heat as compared to CO2.
Why should methane levels matter to us, you might ask?
In order for the world to limit the global temperature to 1.5oC, it is imperative for governments to keep a check on their methane levels as it has a larger global warming potential and controlling it could help reduce warming over the next 20-30 years.
This is where the problem begins, even though methane levels in the last few years have spiked scientists have been unable to explain what is causing it.
Atmospheric Methane is mostly biological in origin. 20 percent is fossil methane i.e. methane trapped in fossils which is released directly from the ground (leaking) into the atmosphere. Microorganisms that break down organic matter produce the other 80 percent.
While the origins of the gas are clear, the various hypotheses of its increasing levels vary vastly.
One study pinpoints fossil fuels as the culprit. The study argues that a simultaneous increase in atmospheric ethane proves that the natural gas industry is at fault. It claims that extracting and transporting fossil fuels lead to major methane and ethane leaks through wells, pipes and other infrastructure. However, the decrease in carbon-13 isotope over the years (a rare isotope of methane, used to calculate methane levels in pipelines) indicates the opposite trend.
Other studies have shown that the rise in methane levels is driven from the emissions of biogenic sources like wetlands, ruminants and paddy fields, all of which are major natural sources of methane. One study of biogenic sources blames the rise in paddy production in developing countries particularly India and China. Another study points out to the current state of wetlands, which have been getting warmer making it ideal for methogens to thrive in.
However, a recent study by NASA claims to have finally solved the mystery by pitting the previous hypotheses against each other. The team led by Josh Worden of NASA’s Jet Propulsion Lab, examined methane molecules linked to various sources. The team focused primarily on isotopes, as methane molecules do not consist of identifying features that reveal their origins.
Worden’s research stacked up all the data of methane release from various sources indicated in previous studies and compared it to the actual levels of methane being recorded. This showcased an anomaly where the total data exceeded the actual limits.
NASA pointed out a third factor in play, Bushfires. After the team reviewed satellite data, ground level measurements and chemical analysis from different emission sources. It turned out that a drop in bushfires around the world between 2006 and 2014 meant a drop in methane levels from those fires as well. “Fire related methane pollution dropped twice as much as previously believed” quoted the study.
Using this data NASA’s study pointed out an average of 12-19 teragram per year increase in methane levels due to Fossil Fuels, 12-16 teragrams increase due to biogenic sources like paddy fields and 4-5 teragram decrease in levels due to decreasing bushfires.
NASA’s study helps resolve the inconsistency in comparing actual methane levels to predicted ones by taking into account bushfires. It also clearly indicates fossil fuels as the biggest contributor to the rise in methane.
However, skeptics point out that the study conducted relied on satellite measurements of carbon monoxide, which like methane is a by-product of incomplete combustion, but whose decline may be down to the shift away from leaded patrol.
The study also doesn’t take into account the atmospheric hydroxyl concentrations which are water molecules stripped off of one hydrogen atom. This compound acts as a volatile detergent essentially cleaning up all the methane from the atmosphere by reacting it with CO2 and water. Dr. Alexander Turner of the University of California believes this compound is less than what it was before, which in turn is causing methane levels to rise. However, as there is currently no reliable way of measuring hydroxyl atoms, the research was carried out using mathematical models.
Each study gives a different outlook on the methane situation and one can only hope that NASA’s claims are true as fossil fuel reductions are easier to manage than changing dietary preferences of countries (in relation to paddy fields), the prospect of wetlands becoming warmer is also dangerous and one we cannot control. As for the decrease in hydroxyls, it would be difficult in finding the true cause of its depletion.
As the onus of reducing methane mostly falls on the oil and gas industry, one can follow the footsteps of British Petroleum (BP) who upgraded all but 145 of its American rigs, fitting them with less leaky pipes and plumbing attaining a leakage rate of 0.2% As per a study conducted by Princeton University if all the gas industries reached the same level of leakage rate as BP then the world would be avoiding the release of 100 tonnes of methane per year.
It is important for the world to take into account the emissions of methane. Beside it being a bigger heat trapper, scientists fear that the increase in global temperatures could result in setting off a natural methane bomb. The arctic soil contains methane which is 2.3 times the CO2 released since the 1800s. Even, though current readings show a steady rise in the methane released from the arctic soil, an extreme rise in global temperatures could set off the release of apocalyptic levels of methane in the air.
With the second half of the United Nations Climate Change Negotiations in Bonn being underway; it will be interesting to see how the guidelines will incorporate methane emissions and how stringent its implementation is going to be for the countries. Methane will never be able to replace CO2 as the most important climate polluter but in order to reach the goals of the Paris Agreement it is important to start finding ways of curbing methane levels rather than solving its mystery.
Link(s): NASA Observatory; National Oceanic and Atmospheric Administration