Why are methane levels rising? Because they shouldn’t be. The IPCC assumed carbon dioxide would be the problem – they had no idea that methane would be so troublesome, even if seepage rates from the natural gas industry were a little higher than they should be.
During much of the 20th century, the amount of methane (CH4) in the atmosphere, mostly from fossil fuel sources, maintained a steady rise. Then, between 1999 and 2007, for reasons that are still obscure, levels stabilized at around 1780 ppb (parts per billion). 1 But in 2007, levels starting rising again. Recently, the rate of increase has accelerated significantly. 2
In 2014, atmospheric methane levels grew by 12.7 ppb; in 2015, by 10.1 ppb; in 2016, by 7 ppb; in 2017, by 7.7 ppb; and in 2018, by 10.77 ppb, reaching a peak of 1900 ppb in November 2018. 3 Growth has been worldwide, notably in the tropics and subtropics of the Northern and Southern Hemispheres.
Because CH4 is one of the most potent greenhouse gases – which over a 20 year period traps 84 times more heat than carbon dioxide – rising levels in the atmosphere are certain to boost the greenhouse effect, thus presenting a major challenge to reaching the goals laid out in the Paris Climate Agreement (2015), namely, to limit global warming to 2°C (3.6°F) or, if possible, to 1.5°C (2.7°F) above preindustrial levels. 4 Meantime, more methane simply worsens the environmental effects of fossil fuels on the biosphere.
Perhaps the most disconcerting feature of this rapid rise in atmospheric methane is the fact that scientists still aren’t sure why it’s happening. Several possible causes have been mooted, but no definitive evidence has yet emerged.
“What we are now witnessing is extremely worrying,” says, Professor Euan Nisbet of Royal Holloway, University of London, and author of several key studies on this topic. “It’s particularly alarming because we are still not sure why atmospheric methane levels are rising across the planet.”
- Change In Methane’s Isotopic Ratio From Positive To Negative
- Methane Levels Must Be Contained To Meet Paris Climate Goals
- Methane Traps More Heat Than Carbon Dioxide
- So Why Are Methane Levels Rising?
- Theories About Rising Levels Of Methane
- Microbial Methanogenesis In Tropics & Sub-Tropics
- Intensive Farming In Africa
- Methane Emissions From Natural Gas
- What’s The Latest Estimate Of Global Emissions From The Oil & Gas Industry?
- What’s The Answer: Why Are Methane Emissions Rising?
Change In Methane’s Isotopic Ratio From Positive To Negative
There is one clue. During the twentieth century and especially during the 1980s, methane’s isotopic ratio (expressed as d13CCH4, pronounced “delta C thirteen CH4”) showed a sustained shift to more positive values. This usually indicates a strong contribution from fossil fuel sources like gas leaks and coal emissions. 5
However, since 2007, methane’s isotopic ratio (expressed as d13CCH4, which is pronounced “delta c thirteen CH4”) has changed to negative. 6 This suggests that the cause of the sudden rise in CH4 is either a change in the mixture of emissions from the various biogenic (methanogenesis), thermogenic (volcanic) and pyrogenic (burnt biomass) sources of methane, or a decline in the atmospheric neutralization of methane by the hydroxyl free radical (OH), (the largest methane sink), or both. 7
Methane Levels Must Be Contained To Meet Paris Climate Goals
Creating a global climate change mitigation strategy is an incredibly difficult task. There are so many climate forcings (primary drivers) and climate feedbacks (secondary drivers) to monitor and assess, so many possible outcomes to plan for and mitigate, that you have to make certain assumptions or else nothing gets done. So, when the Intergovernmental Panel on Climate Change (IPCC) produced its Fifth Assessment Report (AR5) – the scientific basis for the Paris Climate Agreement (2015) – it assumed that reducing methane emissions would be comparatively easy and that the really hard job would be cutting emissions of carbon dioxide (CO2). 8
As a result, all the climate projections in AR5 assume that atmospheric methane is going to drop by 10 ppb between 2010 and 2050. Alas, as we show, methane has actually risen by an average of 9.6 ppb each year since 2014. This has huge implications for the viability of the Paris climate goals.
Dr Sara Mikaloff-Fletcher, an atmospheric scientist at the National Institute of Water and Atmospheric Research in Wellington, New Zealand, explains: “We urgently need to determine why atmospheric methane continues to rise and whether it is possible for humans to slow it,” she said. “If atmospheric methane continues to rise at current rates, it means we need to reduce carbon dioxide and other greenhouse gases even more drastically than previously thought.”
Methane Traps More Heat Than Carbon Dioxide
Methane may be less well known than carbon dioxide, but it’s one of the most damaging greenhouse gases on the planet. Its global warming potential over 20 years is 84 times greater than that of CO2. And despite being 200 times less abundant than CO2, man-made methane accounts for 16 percent of global greenhouse gas emissions, or 8.8 billion tons of CO2 equivalent per year. 9
So where does methane come from? It comes from (a) methane-producing organisms inside cows’ stomachs, (b) seepage from coal mines, as well as natural gas and petroleum installations, (c) methane-making microbes (methanogens) that live in wetlands, bogs and rice paddies, as well as landfill and waste disposal sites. These are the main sources of methane emissions, although there are at least two huge frozen reservoirs of methane, whose stability is critical to our climate system and the health of the planet. These are the sea-bed reservoirs of methane clathrates – a form of methane-filled ice – and the massive expanse of permafrost in and around the Arctic and Antarctica. Any major release of methane from these two sources would be a climate science nightmare, owing to its powerful heat-trapping ability.
Methane’s only weakness is its relatively short atmospheric life-span of about 10 years. This is mainly due to the neutralizing effect of the hydroxyl free radical (OH) – known as the “detergent” of the troposphere because it “cleans up” a number of pollutants. The hydroxyl reacts with methane to create water vapor and the less damaging greenhouse gas CO2. 10 In addition, methane is consumed by methanotrophs in damp soils, although this occurs on a much smaller scale than the hydroxyl’s atmospheric ‘cleansing’.
So Why Are Methane Levels Rising?
In view of the fact that methane’s isotopic ratio has gone negative, there seems to be four possible explanations for the rapid rise in methane levels.
1. First, an increase may have occurred in isotopically negative emissions, from cattle, wetlands or waste, or all three. Such an increase in the proportion of emissions from biogenic sources may account for both the increase in the total methane and the shift in d13CCH4 7 See also: Greenhouse Gas Statistics Lack Consistency.
2. Alternatively, there might have been a strong rise in methane emissions from oil and gas. 11
Methane emissions from fossil fuels are mostly isotopically positive. So, this possibility is only feasible if either (a) the new fossil fuel emissions are markedly more negative than usual, or (b) there has been a simultaneous decline in a source of much more positive emissions, such as those from biomass combustion 12 or (c) both.
In the case of the Worden study (2017), the team sought to explain the average 8 ppb increase in atmospheric methane after 2006, which is roughly equivalent to a net emission increase of 25 million tonnes of CH4. It showed that about 17 million tonnes of the increase are due to emissions from fossil fuels (gas, petroleum), another 12 million tonnes come from wetlands or rice farming, while biomass burning is down by about 4 million tonnes a year. This gives a net increase of 25 million tonnes a year — the same as the observed increase.
3. Thirdly, both the first two options may have occurred. This would explain the rise in total methane, provided that the rise in biogenic emissions is sufficiently larger than the rise in fossil fuels, so that the isotopic value of the total source is negative.
4. Another explanation for the overall increase in emissions is that the power of atmospheric hydroxyl free radicals (OH) may have declined, thus allowing more methane to survive in the troposphere. A slowdown in methane destruction would have a strong isotopic impact. If this explanation is correct, total methane emissions may have changed hardly at all if the isotopic change has been caused by a reduction in the OH sink. On this latter point, a 2017 study determined – with a 64–70 percent probability – that a reduction in OH has contributed to the post-2007 methane rise. 13 If true, this is bad news for Planet Earth, since it would mean that every molecule of methane that entered the atmosphere would now have an increased chance of surviving for longer.
Theories About Rising Levels Of Methane
In their attempt to answer the question – why are methane levels rising? – research teams have produced feasible estimates for the two most likely sources of the increase: (a) microbial methanogenesis in wet tropical and sub-tropical environments like marshes and rice paddies, and (b) emissions from the oil and gas industry.
Microbial Methanogenesis In Tropics & Sub-Tropics
Back in 2011, lack of cloud cover over China enabled the European Space Agency’s Envisat satellite to record data measurements of the Sichuan Basin – a fertile, low-lying area in southwestern China. The data revealed that sub-tropical Sichuan was emitting more methane into the atmosphere than anywhere else in the world. Why? Because of its natural gas installations, and its many rice paddies and animal farms. The Indo-Gangetic plain as well as areas in eastern China – both important sub-tropical farming areas – also had noticeably high emissions. 14
One of the latest of several studies of methane in the tropics, was done by researchers led from Edinburgh University. Using the Japanese GOSAT satellite to monitor greenhouse-gas concentrations over wetlands in East Africa, they identified significant surges in methane emissions above the Sudd wetlands in South Sudan centered on the years 2011-2014. Data on rising temperatures, levels of precipitation and higher than usual feeder-lake water levels, as well as gravity measurements of the weight of water held in the ground, confirmed the scientific basis for these increased emissions.
Dr Mark Lunt, lead-author of the study, explains. “The levels of the East African lakes, which feed down the Nile to the Sudd, increased considerably over the period we were studying. It coincided with the increase in methane that we saw, and would imply that we were getting this increased flow down the river into the wetlands.” 15
Intensive Farming In Africa
Another answer as to why methane levels are rising might be livestock. Some researchers consider that the spread of intensive farming (including cattle farming) in Africa, may be contributing to elevated methane levels, in particular in tropical areas that are becoming warmer and wetter due to climate change. Wetter and warmer swamps are adding to the problem, it is argued.
This theory is now being investigated by a group led by Professor Euan Nisbet of Royal Holloway University of London, who recently gathered a series of air samples over Uganda and Zambia to check for signs of methane.
“We have only just started analysing our data” Nisbet says, “but have already found evidence that a great plume of methane now rises above the wetland swamps of Lake Bangweul in Zambia.” 16
Methane Emissions From Natural Gas
Natural gas consists primarily of methane. But how does it get into the atmosphere? Simple. Natural gas infrastructure around the world consists of millions of miles of pipes, a vast quantity of valves, fittings, vessels, compressors, pumps and other components that operate 24 hours per day, 7 days per week. Natural gas can travel thousands of miles from the extraction site to the end user.
The Yamal-Europe pipeline, for example, connecting the natural gas reserves of Western Siberia to Austria, stretches for 4,196 kilometers (2,620 mi) across Russia, Belarus, Ukraine, and Slovakia through 14 compressor stations. During such journeys, the methane gas has many opportunities to leak into the atmosphere. This includes seepage from faulty components as well as deliberate venting of gas during regular operations.
Is Fracking The Reason Why Methane Emissions Are Rising?
A recent study asked the question: Is shale gas a major driver of recent increase in global atmospheric methane? 17 It’s a fair question. About two-thirds of all new natural gas global production over the last decade has been shale gas produced in the U.S. and Canada using fracking (hydraulic fracturing), a method which causes more methane emissions and is more environmentally harmful than conventional methods.
What’s The Latest Estimate Of Global Emissions From The Oil & Gas Industry?
Methane emissions from the oil and gas sector were just under 2.4 billion tonnes of CO2 equivalent, in 2017. This accounts for roughly 6 percent of greenhouse gas emissions from fossil fuels.
In the United States, methane emissions from the natural gas sector alone total 2.3 percent of all gas moved by pipeline – at an estimated loss in revenue of over US$1 billion per year. Roughly speaking, it’s the same as the annual exhaust emissions from 70 million passenger cars. Studies show that if methane leaks are greater than 3%, not only is it bad for climate change but in addition there are no immediate climate benefits from closing down coal-fired power plants in favor of natural gas power plants. So, the dream of natural gas being the transitional energy between the fossil fuel era and the renewables era would be over.
So can these natural gas leaks be prevented? In theory, Yes. In practice it’s a different story. The global gas infrastructure is so vast, it is simply not possible to check valve or fitting for possible seepage. The only practical way to reduce methane emissions from gas installations is to take measurements from as many different types of components as possible. This way you might identify the really bad leaks, which probably account for half to three quarters of all methane released into the atmosphere from the natural gas industry. 18
Trouble is, the more gas we consume and the more pipelines that are built, the more methane we emit.
Wait till the West-East Gas Pipeline, operated by PetroChina, is completed. Consisting of a main trunk line and eight branches, it links the Tarim Basin gas fields in Xian Jing to Shanghai, and stretches for 4,000 kilometers (2,500 mi), passing through a total of 66 cities in ten provinces. When fully completed it will stretch for over 8,000 kilometers (5,000 mi).
Methane Emissions From The U.S. Ammonia Fertilizer Industry
In a recent study 19 researchers took air samples from six U.S. ammonia fertilizer plants, constituting 25 percent of the industry in America. It’s an industry that uses natural gas as a feedstock and a fuel for the production of ammonia and other upgraded products.
Findings showed the plants had a natural gas leakage rate of roughly 0.34 percent. If the plants are representative of the industry as a whole, then total methane emissions are estimated to be 29,000 tonnes of methane per year, in 2015–2016. This is way higher than the official EPA figures of 200 tonnes of methane, per year.
According to John Albertson, co-author of the study, “We took one small industry that most people have never heard of and found that its methane emissions were three times higher than the EPA assumed was emitted by all industrial production in the United States.”
What’s The Answer: Why Are Methane Emissions Rising?
Methane is hard to track, hard to quantify, and subject to natural influences even when its emissions are entirely man-made. There are sources we don’t know about and sinks we don’t fully understand. Frankly, it’s amazing that scientists know so much about it.
There’s not likely to be one answer to the rise in emissions. It’s almost certain to involve an annoyingly imprecise combination of methanogenesis, natural gas emissions, intensive farming – all amplified by a continuing rise in global temperature, perhaps made worse still by a decline in the cleansing power of OH. Whatever the answer, we need to find it, and fast.
For the latest statistics on emissions of F-gases – the most powerful heat-trapping gases on record, see: F-Gases: Fluorinated Greenhouse Gases.
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