Airborne research on flow of greenhouse gas takes off

Chasing storms and satellites with a plane — that’s what Penn State researcher Ken Davis and his NASA-funded research team will spend part of their summer doing. The team, which is scheduled to start its first research flight next week, will be taking a new approach to studying how weather transports greenhouse gases across different regions of the U.S.

Davis, professor of atmospheric and climate science, is leading the Atmospheric Carbon and Transport–America, or ACT-America, project, which received a five-year, $30 million grant from NASA. Its main objective is to advance our ability to predict and manage future climate change by improving our ability to quantify the sources and sinks of methane and carbon dioxide, the two most important anthropogenic greenhouse gases.

Where has all the carbon dioxide gone?

Tracking the movement of greenhouse gases starts with identifying their sources. The greenhouse gas carbon dioxide is the largest contributor to global warming, and the majority of current emissions come from burning fossil fuels. A portion of the emitted carbon dioxide remains in the atmosphere where it absorbs infrared radiation, thereby contributing to the atmosphere’s greenhouse effect. Some of the emitted carbon dioxide is absorbed by ‘sinks’ such as forests, growing crops, and the ocean.

What complicates the task of tracking the flow of carbon dioxide is that a sink can also be a source depending on the context.

“Forests absorb carbon dioxide during the day in the summer through photosynthesis but emit carbon dioxide at night, and all winter, through respiration,” said Davis. “What we need to know is whether a particular ecosystem is, over the course of a year, a net sink or source.”

Researchers use a variety of methods to measure greenhouse gas sources and sinks, from determining the change in diameter of trees over time to measuring satellite images of leaf area. So far, these methods haven’t collected enough data to conclude what regions of the biosphere are slowing climate change by absorbing carbon dioxide.

“There’s an imbalance in our biosphere now that causes it to remove about a quarter of the fossil fuel carbon dioxide emissions every year, but we don’t know where or why this is happening,” said Davis. “We have some evidence and hypotheses, but current measurements of this removal aren’t accurate enough to provide conclusive results.”

By collecting data via airplane from large geographic regions of the U.S., Davis and the ACT-America team hope to shed light on this mystery. The breadth and scale of this data collection is unprecedented and, combined with currently available data, could help scientists infer the sources and sinks of carbon dioxide.

Mysterious methane

Atmospheric methane is at a higher level today than it has been in the past 800,000 years and it has more than doubled since pre-industrial times. In the past several decades, the atmospheric concentration of methane has been increasing, overall, except for several years in the early 2000s when it leveled out. Researchers don’t have enough data on methane sources to explain why that increase temporarily tapered off.

Methane sources have been somewhat elusive because methane emissions are often not reported.

“While carbon dioxide emissions are fairly well known because we pay for fossil fuels, methane emissions come from sources that have no similar accounting system – for example, leaks from oil and gas mining, emissions from animal agriculture, and emissions from wetlands,” he said. “Methane emissions, therefore, are quite uncertain.”

The ACT-America team will measure methane levels directly on a region-by-region basis, reducing uncertainty in emissions for these regions.

“Hopefully the data we collect on the concentration of methane will be able to tell us how much methane is coming from the regions we are flying over,” said Davis.

Quantifying regional sinks and sources

Flying giant lawnmower patterns in the sky across several states, the team will use an array of instruments to measure the concentrations of carbon dioxide, methane, ozone, carbon monoxide and other gases. They will also measure aspects of the weather, such as temperature, wind velocity and pressure, in both stormy and fair conditions to assess how weather systems transport greenhouse gases.

“If I measure the difference in concentrations of greenhouse gases between New York and Virginia and want to figure out what is going on in between, I need to know how fast the wind is blowing, what direction, and how deep the convective mixing is,” he said. “If I get that wrong, I get inference of sources and sinks wrong, too.”

The team will also track NASA’s Orbiting Carbon Dioxide Observatory, which was launched in 2014 and records carbon dioxide levels around the globe. By taking measurements while flying under the satellite’s orbit, the team will be able compare their results with the satellite’s to evaluate the accuracy of the satellite data.

In July they will take off from Langley and the Wallops Flight Facility, Virginia, to study the mid-Atlantic region. In early August, they will depart from Lincoln, Nebraska, to measure gases above the Midwest. In mid-August they will fly over Shreveport, Louisiana to analyze the southeastern U.S. The team will spend two weeks collecting data in each location. Over the next five years, they will repeat this flight plan four more times at different times of year to continue building the baseline data needed to infer the sinks and sources of greenhouse gases.

Each location will provide data on different types of sources and sinks. The Midwest is where many storms take shape downwind of the Rocky Mountains and is also home to intensive agricultural activity. In the southeastern U.S., researchers can see how sea breezes from the Gulf of Mexico and resulting coastal storms mix with extensive forests, and oil and gas production facilities affect greenhouse gas concentrations. In the mid-Atlantic, the team will investigate the impacts of oil, gas and coal production, forest cover, and major metropolitan areas on greenhouse gas concentrations.

“We don’t have dense enough measurements to map out the flow of greenhouse gases in weather systems; that’s what we’re going to fix,” said Davis. “We’re going to find weather systems that are moving these greenhouse gases around, get inside them and find out what’s happening in space and time. These data should ultimately help us update the models the scientific community uses to simulate the future of the Earth’s climate system.”

ACT-America is a five-year, $30-million project funded by NASA. NASA Langley Research Center, located in Hampton, Virginia, is Penn State's lead partner in the effort, and the project also includes researchers from Colorado State University, the University of Colorado Boulder, the Harris Corporation, the University of Oklahoma, the Carnegie Institute of Science, the National Oceanic and Atmospheric Administration, Oak Ridge National Laboratory, NASA Jet Propulsion Laboratory and NASA Goddard Space Flight Center.