Last month, scientists working with data from Tropomi, a monitoring instrument onboard the European Space Agency’s Sentinel-5 satellite, published some startling findings. Writing in the journal Science, the team reported that it had found about 1,800 instances of huge releases of methane (more than 25 tonnes an hour) into the atmosphere in 2019 and 2020. Two-thirds of these were from oil and gas facilities, with the leaks concentrated over the largest oil and gas basins across the world, as well as major transmission pipelines, the team said. Launched in 2017, Tropomi has been a huge step forward for scientists researching methane, being the first instrument in space that can see plumes of methane emissions directly, says Lena Höglund-Isaksson, a methane researcher at the International Institute for Applied Systems Analysis . For example, the instrument led to the discovery of huge methane leaks in Turkmenistan that researchers were not aware of before, she says. But these emissions are only the tip of the methane iceberg. “The current constellation of satellites in orbit around the planet today can see about 10% of the methane emissions of oil and gas on the planet,” says Riley Duren, chief executive of Carbon Mapper and a researcher at Arizona University, who co-wrote the paper. “The remaining 90% of these oil and gas methane emissions are below the detection limit of that satellite, but they won’t stay undetected for long.” Better detection of where the methane is coming from is becoming a global imperative. An analysis last month from the International Energy Agency found that methane emissions from oil, gas and coal are about 70% higher than what governments are officially reporting. If the world is ever going to achieve significant reductions of this gas, it needs to know where it’s coming from. In the next few years, several new satellites with far higher resolutions are set to be launched, including MethaneSat, scheduled for launch by the US nonprofit Environmental Defense Fund (EDF) in early 2023, and the first two satellites from Carbon Mapper in late 2023; the latter plans to have a whole “constellation” of them in orbit by 2025. These satellites will allow an unprecedented tracking of the sources of this potent greenhouse gas and, it’s hoped, ultimately help to stop the emissions occurring in the first place. Methane is the second largest contributor to climate change after CO2, but until recently has received far less attention when it comes to climate action. “Historically, the world has focused so much on stabilising the climate in the long term and the way to do that is to reduce CO2 emissions,” says Ilissa Ocko, a climate scientist at the EDF. While methane lingers for far less time in the atmosphere than CO2, it is a much more potent warming gas in the short term. Twenty years after its release, it is more than 80 times as powerful as CO2; after 100 years, the figure is reduced to about 30 times. This means that methane has an outsize impact on global warming in the short term. Methane emissions have been rising – they increased by around 8-10% between 2000 and 2017. In its sixth assessment report, published last year, the Intergovernmental Panel on Climate Change warned that anthropogenic (human-caused) methane is responsible for about a quarter of the 1.1C warming we are seeing today, while a UN report last year said cutting methane emissions by 45% would avoid 0.3C of warming by the 2040s. Tackling methane will have a huge impact on whether the world manages to keep the global temperature rise below 1.5C. “Up until relatively recently, we really didn’t have a full understanding of just how much of an impact methane was having on our climate,” says Jonathan Banks, international director for super pollutants at the Clean Air Task Force. “[But] methane, because it’s a short-lived climate pollutant, gives us an opportunity to actually slow down warming. Because it’s not just how warm the planet gets, but it’s also how fast we heat up that matters.” After decades of focusing on CO2, last year more than 100 countries signed up to a pledge at the Cop26 climate change conference to slash global methane emissions by 30% by 2030 compared with 2020 levels. “It was really exciting to see us really turn a corner on methane awareness and methane action,” says Ocko. “To have a separate target for methane is just huge.” She reckons the target is as ambitious as it could have been to get more than 100 countries to sign on, although more could be done with available technologies. One of the problems with methane, however, is that it is not always easy to know where it is coming from. “If countries want to meet these 30% reduction targets, then we have to have some kind of way to verify it,” says Höglund-Isaksson. The vast majority of methane emissions on the planet from human activity remain “invisible” today because they’re not being monitored – at least not comprehensively and not regularly, says Duren. Naturally, wetlands are a huge source of methane, but these emissions are now far superseded by man-made emissions from fossil fuel production, agriculture and waste. Agriculture is the largest man-made source of methane, mostly from cows (which emit methane both through their burps and their manure) and rice (which emits methane when fields are flooded). There are already moves to tackle these, from the use of different systems of rice production to the variety of proposed ways to stop cows emitting so much methane (or simply reducing meat consumption altogether). The issue here is less of detection than action, but the more dispersed nature of agriculture means this will be a slow ship to turn. Landfills can also release a significant amount of methane, but there are solutions here, too: landfill gas can be captured and used, which also reduces local air pollution. Spotting large sites of methane release from space will be helpful, says Banks, by helping to direct international attention and, ultimately, money to the worst emitting sites. However, a study published last year by the EDF found that it is the fossil fuel industry that has the most potential to cut methane emissions easily in the short term. The study found that a full 50% of methane emissions from the oil and gas sector could be cut by 2030 without incurring any net costs. Overall, the study found that around a quarter of global methane emissions could be reduced with cost-effective measures, an amount that would already bring the world close to the 30% target, says Ocko. Methane is the main component of natural gas and is emitted in the oil and gas industry whenever natural gas is released into the atmosphere, rather than combusted to CO2. There are three main sources: intentional venting of methane gas; incomplete flaring, where gas is deliberately burnt rather than sold, but does not fully convert to CO2; and unintentional “fugitive” emissions from accidental leakages, such as through a faulty seal. A substantial amount of methane is also released through coalmining, as methane found near coal is often vented away to avoid explosions. Detection technology is instrumental in helping to plug the leaks in the oil and gas industry, says Ocko. “Sometimes, just tightening a valve or replacing a gasket or tuning an engine – it’s really simple plumbing that you can do to prevent these leaks from occurring. The challenge is just knowing where these are.” The methane pledge at Cop26 has given a boost to efforts to cut emissions. But some scientists and non-profit groups are already way ahead of the politicians on how to do this. For years now, they have been working on the next step in methane detection: a new generation of satellites that will bring a far deeper insight into exactly where emissions of methane are happening on the planet. “Over the next two to three years, you’re going to see an expanding constellation of methane monitoring satellites that will give us a more expansive view of the methane iceberg,” says Duren. These satellites will give an unprecedented overview of where the methane is being emitted and help to guide operators and decision-makers in their efforts to reduce it. The satellites The first of these is EDF’s MethaneSat, set to start delivering data in 2023. MethaneSat will have unprecedented precision compared with Tropomi, says Ocko. It will be able to capture leaks as low as 5kg per hour per sq km, far below the 25 tonnes an hour that Tropomi can see, and will provide near-global coverage. “It will provide information for how much emissions are coming from a certain area, that then can be aggregated for specific countries, so you’ll be more informed about what your baseline emissions are,” says Ocko. “You will also be notified when there are large leaks, [or if] there’s something all of a sudden unusual that happened. And so you could go in and determine the source and fix it as soon as possible instead of letting it leak continuously.” MethaneSat will be particularly useful to better understand the methane coming from those parts of the world where it is harder to fly an aircraft carrying a sensor, such as Russia, adds Ocko. “[It] will have unprecedented precision for identifying those sources of methane globally and so that will be really helpful in terms of completing the puzzle further in terms of what emissions are globally from oil and gas.” Carbon Mapper’s satellites, meanwhile, will be able to focus on individual methane sources with a spatial resolution of just 30 metres (98ft). Its ultimate goal is to provide “daily to weekly monitoring of all of the high-emitting regions around the planet and to make that methane data and CO2 data publicly available,” says Duren. Once all 20 satellites are in orbit in the mid-2020s, Carbon Mapper hopes to increase satellite detection to about 90% of oil and gas sector leaks. What is great about both satellites going up together is that they are complementary to each other, says Banks. EDF’s MethaneSat is more like a wide-angle lens, he says, and will see a lot more of the planet. Carbon Mapper’s satellites, meanwhile, are more like a telephoto lens, allowing a zoomed-in view of specific sources. “So they work together. I think they will dramatically change our perception of this problem.” Getting to the level where we can detect emissions directly from the sites begins to make it possible for governments to hold individual companies responsible for emissions, says Höglund-Isaksson, and to verify whether emissions are continuing. Up until now, there has been no way to monitor sites continuously, she notes. “We were stumbling in the dark a bit because we didn’t have any way to verify emissions at the source level,” she says of her work looking at the origins of methane emissions. There are other useful methods for detecting sources of methane emissions, such as handheld optical gas imaging cameras and remote sensing measurements taken from planes. These networks will remain more sensitive to smaller, local-scale emissions, says Ann Stavert, a scientist at the Global Carbon Project at the Commonwealth Scientific and Industrial Research Organisation’s Oceans and Atmosphere department in Australia. “Satellites have an important role to play, but expansion of ground-based observations will be just as important,” she says. “There is no magic bullet in terms of methane observation infrastructure – a range of approaches is needed.” As global leaders narrow in on reducing methane for climate reasons, understanding where the methane is coming from will become more and more important. “It’s been said many times before: you can’t manage what you don’t measure,” says Duren. “The truth today is that the vast majority of methane emissions on the planet from human activity remain invisible.” The methane leaks in our kitchens It may not be detectable by satellite, but researchers have flagged another worrying source of methane. A study in January this year found that gas stoves in about 40m US homes release methane through incomplete combustion while cooking and via leaks when the stove is turned off. While any reduction in emissions is a good thing, at less than 0.1% of US methane emissions, it is likely gas stoves are only responsible for a small component of the total, says Stavert. However, burning gas also emits CO2, so choosing electric cooking is still a good step for cutting carbon, she adds. Another problem with gas stoves is their health impact: tens of millions of Americans cooking with gas stoves are probably experiencing levels of indoor nitrogen dioxide pollution that would be illegal if outside, a 2020 report found.