Keeping an eye on methane
NASA creates a 3D portrait of its sources and movements.
By Nick Carne
NASA is tracking methane to get a better handle on how and where it moves, and how it behaves when it gets there.
Its scientists have created a 3D portrait of methane concentrations by combining multiple data sets from emissions inventories and simulations of wetland sources into a high-resolution computer model.
Carbon dioxide is the main contributor to global warming because its concentrations are higher than methane and it has a longer lifetime. However, a molecule of methane is more efficient at trapping heat than a molecule of carbon dioxide.
Methane also has many more sources, and “[t]here's an urgency in understanding where the sources are coming from so that we can be better prepared to mitigate methane emissions where there are opportunities to do so," says NASA’s Ben Poulter.
"Methane is a gas that's produced under anaerobic conditions, so that means when there's no oxygen available, you'll likely find methane being produced."
To create a global picture of that production, Poulter and colleagues used data from emissions inventories reported by countries, NASA field campaigns such as the Arctic Boreal Vulnerability Experiment (ABoVE), and observations from the Japanese Space Agency's Greenhouse Gases Observing Satellite (GOSAT Ibuki) and the Tropospheric Monitoring Instrument (TROPOMI) aboard the European Space Agency's Sentinel-5P satellite.
They combined the data with a computer model that estimates methane emissions based on known processes for certain land-cover types, such as wetlands, and also simulates the atmospheric chemistry that breaks down methane and removes it from the air.
Then they used a weather model to see how methane travelled and behaved over time while in the atmosphere. Several locations stood out.
In South America, the Amazon River basin and its adjacent wetlands flood seasonally, creating an oxygen-deprived environment that is a significant source of methane.
The methane signal is not as strong over Europe, where sources are influenced by the human population and the exploration and transport of oil, gas and coal from the energy sector.
In India, rice cultivation and livestock are the two driving sources of methane, while China's economic expansion and large population drive the high demand for oil, gas and coal exploration for industry as well as agriculture production, which are its underlying sources of methane.
And the Arctic and high-latitude regions are responsible for about 20% of global methane emissions.
"What happens in the Arctic, doesn't always stay in the Arctic," says NASA meteorologist Lesley Ott.
"There's a massive amount of carbon that's stored in the northern high latitudes. One of the things scientists are really concerned about is whether or not, as the soils warm, more of that carbon could be released to the atmosphere.
“Right now, what you're seeing in this visualisation is not very strong pulses of methane, but we're watching that very closely because we know that's a place that is changing rapidly and that could change dramatically over time."
Poulter says one of the challenges with understanding the global methane budget has been to reconcile the atmospheric perspective on where we think methane is being produced with the bottom-up perspective – or how we use country-level reporting or land surface models to estimate methane emissions.