One of the central outcomes of COP26, the recent Glasgow climate summit, was the Global Methane Pledge to cut the emissions of methane to the air by 30 per cent by 2030. That’s a tough challenge. The proportion of methane in the air has just reached 1,900 parts per billion (ppb). Three centuries ago, before human industrialisation, it was about 700ppb.
The amount of methane in the air – the atmospheric methane ‘burden’ – increased strongly in the 1980s, but then stabilised. But methane began rising again in 2007. In many years this growth was led from the tropics and sub-tropics, but at times the high north also led. Currently methane’s growth rate – 17 ppb in the year 2021 alone – is the fastest in the detailed observational record that began in the early 1980s.
Methane is a powerful greenhouse gas. Although 1900 ppb is less that 2 ppm (parts per million) in the air, compared to over 400 ppm for CO2, methane has a warming impact much greater than CO2, molecule for molecule. The recent Intergovernmental Panel on Climate Change report has estimated methane’s warming impact on global surface air temperature, including knock-on impacts, to be over half a degree Celsius since the year 1750. That’s roughly half the impact of carbon dioxide; so methane is important.
The United Nations’ Paris Agreement expected rapid cuts in methane, not a rise. To get us back to a track that is compliant with the Paris Agreement, the Global Methane Pledge was agreed by over 100 countries at the COP26 climate summit. This Pledge requires 30 per cent cuts in emissions by 2030, to keep the Paris goal of limiting warming to 1.5 degrees Celsius within reach.
The global methane budget – quantifying the major sources and sinks – is still not properly understood. In the air, methane’s lifetime is about 9.1 years. Methane is emitted from both natural sources (roughly 40 per cent), and by human activity (about 60 per cent). Current estimates are that approximately 600 million tonnes are emitted annually into the air.
We have ‘top-down’ scientific estimates from air measurements and global atmospheric models, and also ‘bottom-up’ national statistical submissions to the United Nations Framework Convention of Climate Change, based on data like cow numbers and emissions from fossil fuel production and distribution. But the top-down and bottom-up numbers don’t agree.
Nor do we know if the strong recent growth, much of it led from the tropics and sub-tropics, is caused by increased human activity such as cattle farming, or if new feedbacks are happening, especially in rising emissions from methane-emitting tropical wetlands, with warming feeding more warming?
Emissions can be classified into biogenic (ruminant breath, manure, landfills, sewage, and leaky biodigester facilities), thermogenic (fossil fuels – natural gas and coal) and pyrogenic (crop waste fires and forest fires, mostly human-lit).
Of this, roughly 200 million tonnes come from natural wetlands, from rotting vegetation, and peat bogs. Methane emission comes both from the very productive tropical swamps – especially the Amazon, Nile and Congo basins – and also in summer from the wide boreal wetlands of Russia and Canada (where Canadian beavers are busy methane makers, damming swamps and filling them with cut trees).
Human-driven emissions are very diverse. The sources include the gas industry (at wells, from pipes and compressors, and where the gas is burned, for example in houses), from anaerobic decay in landfills, and from incomplete combustion in biomass fires. Ruminants such as cows, sheep and deer have stomachs that microbiologically are like wetlands, and these animals breathe out methane (front end, rather than flatulence). The gas, coal and oil industries emit around 120 million tonnes annually, cattle about 115 million, landfills 70 million, and fires 30 million tonnes annually.
Why Methane is Rising
The rise in the atmospheric methane burden could be driven by larger emissions, or declining sinks, or both. The major methane sink is hydroxyl, [OH]. Photochemical reactions, especially in very sunny moist tropical air, make [O], which then removes a hydrogen from water, H-O-H, to make two [OH] radicals. These then attack methane, CH4, destroying it by oxidising it to CO2, which is a far weaker greenhouse gas. Other methane sinks are bacteria in moist oxidised soils and chlorine in marine haze. The lifetime in the air of a little over nine years is the amount of methane in the air divided by the annual destruction from the air.
“evidence from bubbles trapped in ice cores shows that the proportion of carbon-13 in atmospheric methane increased for two centuries prior to 2007”
The strength of methane’s sinks clearly varies from year to year, but it’s not clear that there is a strong trend sustained over the 14 years since the methane burden started growing in 2007. That suggests the new growth is primarily driven by increasing methane sources. But which sources? And where are they?
Methane sources can be identified by their characteristic geochemical ‘signatures’. Carbon has two stable forms, or isotopes. Roughly 99 per cent is carbon-12 (or 12C) and about one per cent is carbon-13 (13C). These stable isotopes are not radioactive, in contrast to the much rarer radioactive form, carbon-14 (14C), which is used by archaeologists for dating as it is in all our food, our bodies, and the air that we breathe. Compared to the methane in the air, methane emitted from fossil fuels and fires has slightly more 13C, while biogenic methane from wetlands, cows, sewage and landfills is slightly richer in 12C.
Evidence from bubbles trapped in ice cores shows that the proportion of carbon-13 in atmospheric methane increased for two centuries prior to 2007. This trend was driven by emissions from fossil fuels, especially coal, gas and oil flaring. But in 2007, when the methane burden unexpectedly started growing again, the isotopic trend reversed, and instead trended towards carbon-12.
That change of trend strongly suggests biologically-made emissions from wetlands, cows, sewage or landfill, or several / all of those, has been driving recent growth, post 2007 – not fossil fuel and fire emissions. Moreover, in many though not all of the years since 2007, although there have been episodes of growth in the north, the measurements of the collaborative global network run by the US National Oceanic and Atmospheric Administration (NOAA) suggest that the growth has primarily been led from the tropics and sub-tropics.
This suggests biological emissions from tropical wetlands and/or tropical farming are rising.
Broadly, wetland emissions increase with rising temperature. Rainfall too, has increased recently in important parts of the moist tropics, locally increasing wetlands. Warmth and rainfall support grass growth, and human populations are rising very fast, especially in tropical Africa, demanding food. This may be producing more and better-fed methane-emitting ruminants (cows, sheep and goats), especially as farming and fertilisers may be supporting more grass. Run-off from increasing fertiliser use may also be delivering increased nutrients to wetlands, which may be supporting increased organic productivity and thus methane emissions.
Could methane feedbacks be at work, with warming feeding more warming? Our “MOYA” project (Methane Observations and Yearly Assessment), a consortium comprising teams from 14 UK universities and government research institutes like the UK Centre for Ecology and Hydrology, and the British Antarctic Survey, has been funded by the UK Natural Environment Research Council to study the global methane budget. Publications of its results helped provide the basis of evidence for the 2021 United Nations Global Methane Assessment, and the 2021 UN Emissions Gap Report, both key underpinnings of the 2021 COP26 climate conference in Glasgow, and the Global Methane Pledge, now signed by well over 100 countries.
MOYA work has been very wide-ranging, including on-ground mobile and fixed-site measurement campaigns, low level flights
by drones and aircraft, and satellite studies. This work has been backed up by careful computer modelling of regional and global budgets, linking measurements, meteorological data, and chemical transport studies, essentially running the wind backwards from the measurement points to the sources of the emissions.
Scientific teams in MOYA have been flying aircraft at low level to measure emissions and isotopic signatures from wetlands, farming and fires both in the tropics and the Arctic. Tropical flights have been in Senegal, Uganda, Zambia, and Bolivia, while Arctic and northern forest and bog and wetland fieldwork and aircraft missions have been carried out in Scandinavia, tracking winds from large summer emissions from Siberian wetlands.
The MOYA flights found some huge emissions. Zambia’s Bangweulu wetlands (part of the Upper Congo basin) may emit half as much methane as Britain, or more, while wetlands in Bolivian Amazonia may perhaps emit as much as Britain or more. It’s still not clear if biogenic emissions are increasing through climate warming feedbacks – the warming feeding warming – but it looks likely.
Finding and Quantifying Emissions
Fixing the problem depends on locating human-caused emissions, so that we can stop them. Human or ‘anthropogenic’ emissions are around 60 per cent of total global emissions – thus we need to halve them by 2030 to meet the Global Methane Pledge. It’s a tough challenge, but possible.
But first we need to find the emissions. For that, there have been rapid new technological developments, with a wide variety of new optical instruments capable of very rapid measurements at much higher precision than older instruments in wide use as recently as a decade ago. Mobile platforms include SUV vehicles, UAV drones, and low flying aircraft.
“scientific teams in MOYA have been flying aircraft at low level to measure emissions and isotopic signatures from wetlands”
Royal Holloway’s Greenhouse Gas Group operate the MIGGAS (Mobile Integrated Greenhouse Gas Analysis System) survey vehicle (NERC-funded). This houses state-of-the-art measurement equipment from three makers of accurate rapid instruments: Picarro, LiCor and ABB (Los Gatos Research). These instruments allow the high-precision measurement of a range of atmospheric gases: carbon dioxide, methane, ethane (to identify gas leaks) and 13C of methane (to distinguish biogenic from fossil fuel sources). Coupled to these is the ability to take spot, or grab, samples of air for in-laboratory high precision isotopic measurements.
Royal Holloway’s mobile facility has been deployed since 2021 across the UK and Channel Islands to locate and identify methane sources. Prior to this, an earlier generation of the mobile system was widely deployed across the UK and also in overseas campaigns in Australia, Bucharest, Hong Kong, Kuwait and the Netherlands.
Research flights are also very powerful ways of measuring and sampling emissions. In the MOYA project in Africa and the Arctic and over the North Sea gas fields, we used the UK Facility for Airborne Atmospheric Measurement, an extremely well-instrumented BAe 146 jet aircraft based in Cranfield and equipped with a fast greenhouse gas analyser and sampling flasks.
“atmospheric measurement from a BAe 146 jet aircraft equipped with a fast greenhouse gas analyser and sampling flasks”
In Bolivia, working jointly with colleagues from La Paz, we used one of the British Antarctic Survey’s aircraft on its way north for maintenance.
The Global Methane Pledge
Do we have a realistic chance of fulfilling the Global Methane Pledge, to cut emissions by 30 per cent by the year 2030? – That’s nearly four per cent of cuts in total methane emissions a year. Since human-caused emissions are roughly 60 per cent of the total global methane output, and we can only cut these, then a 30 per cent cut in the total means halving the human-caused emissions over the next eight years to 2030. That’s an extremely challenging target.
Yet it’s not impossible.
The gas industry is the most obvious target. Pumping gas long distances invariably involves gas leaks, for example, under urban roads constantly pounded by heavy trucks. Emissions also come from shipping liquefied natural gas, which emits methane at terminals and during transport, and also carbon dioxide when gas is burned to power refrigeration and compressors. Gas leaks need to be reduced quickly. That’s where the recent advances in detection and measurement can make a huge contribution.
More than that, the current surge in gas prices and the terrible war in Ukraine demonstrate the need to improve Europe’s energy security by moving wholly away from gas. Hydrogen is an alternative, but there are problems – it’s leaky, it’s an indirect greenhouse gas, it’s involved in chemical reactions that have complex impacts on air pollution, and it affects ozone, potentially with damaging impact in the stratosphere. Understanding the hydrogen budget and weighing up the potential benefits and perils of a switch to hydrogen will demand better measurement technology – atmospheric hydrogen measurement techniques have barely changed for 50 years.
Coal mining makes a major contribution to methane emissions. Major coal economies like China, India, South Africa, Russia and Australia will all suffer badly from climate change, but have not signed the Global Methane Pledge. That’s because so many jobs depend on coal, despite the air pollution caused by burning coal.
In the short-term, technology can help, for example, by detecting methane emissions in mine vents and helping with their removal. Moreover steel production needs coal. There is a strong argument for using better quality, stronger steels, which reduces emissions as less steel needs to be made. But construction and engineering steel users need to be persuaded to switch. In the longer term, coal mining needs to end.
Can We More Than Halve Fossil Fuel Emissions by 2030?
That’s not easy but yes, new measurement technology helping to find and identify leaks, alongside modernisation, should make halving emissions possible, especially if the urgency to reduce comes not only from climate concerns, but also from energy security concerns as Europe and China choose to move away from gas.
It will be more difficult to reduce farming emissions. Here again, technology may help as methane removal could be feasible where methane mixing ratios are habitually high, for example around dairy barns. However, there has been very little research on methane removal.
“new measurement technology helping to find and identify leaks, alongside modernisation, should make halving emissions possible”
In many tropical regions cattle are both core supplies of food and, in many nations, also have a central religious or cultural position that needs to be respected. This is so in India, the world’s cow super-power, with by far the most cows; while in many parts of Africa pastureland cows are culturally significant and are vital to feed the fast-growing human populations. Moreover, if pastured ruminants in Africa and South Asia were abandoned as food sources, that would need intensified crop farming and fertiliser use, with likely increased linked methane emissions. Thus in many tropical countries the more immediate choices to reduce methane emissions may be to address crop waste fires, landfills and the coal industry.
For CO2, it’s clear that the industrialised nations have produced most of the historic human-caused emissions. In this decade new CO2 growth is primarily driven by China and India. Methane is different. Emissions from China are important, but since 2007 the tropical and sub-tropical nations seem to have a major role in driving much of the recent methane rise. While much of the growth in tropical emissions may be from natural wetlands responding to climate change, it is clear that tropical anthropogenic emissions may also be large. Thus tropical nations are a central part of the methane problem, and so they need to contribute to finding the solution.
MOYA work shows that cutting methane emissions is possible, even for tropical nations. There’s a chance they too can meet the Global Methane Pledge. An obvious start is to eliminate the very widespread crop-waste fires in Africa, India and SE Asia, that both emit methane and cause severe air pollution. There are alternatives to burning crop waste. Reducing burning is both feasible and will massively help human health by cutting pollution.
Similarly, in the huge new landfills around fast-growing tropical megacities and also in the widespread dumps around smaller cities and villages, all too frequently on fire, emissions can be cut by simple methods like putting on soil coverings. In the longer-term, much agricultural emission growth in the tropics reflects soaring food-production demands under the pressure both of fast-growing populations and fast-rising obesity, now widespread in the tropics. The solutions to these pressures are subtle – female education, social support for the poor and elderly, good health care and diet education, and above all good governance. These all act to stabilise population.
“is there a methane emergency? Yes, there is”
Is there a methane emergency? Yes, there is. But with really vigorous efforts it should be possible to make a very substantial cut in emissions from gas leaks, landfills and waste fires. Whether we can cut human emissions enough by 2030 is going to be very challenging indeed, but given good measurement technology, determined efforts in developed nations, and strong community support within tropical countries, we do indeed have a chance that we can fulfil the Global Methane Pledge.