First Observation of Methane’s Increasing Greenhouse Effect at the Earth’s Surface
Predictions of the direct impacts of greenhouse gases must account for local temperature and humidity conditions.
Methane traps heat in the atmosphere. For the first time, scientists directly measured the increasing greenhouse effect of methane at the Earth’s surface. Measuring the atmospheric absorption of methane is complicated and can be impacted by other gases. The team tracked a rise in the warming effect of methane, one of the most important greenhouse gases for the Earth’s atmosphere, over 10 years at a field site in northern Oklahoma.
This study offers direct measurements. Such measurements are extremely complex. This study shows increasing methane concentrations are leading to an increasing greenhouse effect in the Earth’s atmosphere. It also shows that local temperature and humidity conditions must be taken into account to predict the direct impacts of greenhouse gases.
While atmospheric methane concentrations plateaued between 1995 and 2006, they have since increased and are expected to impact the surface energy balance. The relationship between methane radiative forcing and methane mixing ratios has previously only been calculated using radiative transfer models. Methane spectroscopy is complicated, and methane absorption can be impacted by other atmospheric gases, including water vapor. Researchers determined the methane radiative forcing using a large suite of atmospheric observations from more than 10 years of observations at the Department of Energy’s Atmospheric Radiation Measurement facility Southern Great Plains site in Oklahoma. One major advance in this study is that researchers account for the spectroscopic interactions between methane and water vapor as well as the vertical distribution of water vapor. They detected no significant trend in methane forcing before 2007, but found a significant trend after 2007. They also showed that both methane and water vapor contribute significantly to the methane radiative forcing signal.
This material is based on work supported by the Director, Office of Science, Office of Biological and Environmental Research of the Department of Energy (DOE) as part of their Atmospheric System Research Program, the Atmospheric Radiation Measurement (ARM) Program, the Terrestrial Ecosystem Sciences Programs, and the ARM Aerial Facility. Resources of the National Energy Research Scientific Computing Center were used. Work at Lawrence Livermore National Laboratory was performed under the auspices of DOE by Lawrence Livermore National Laboratory. The National Oceanic and Atmospheric Administration Global Monitoring Division provided data.
D.R. Feldman, W.D. Collins, S.C. Biraud, M.D. Risser, D.D. Turner, P.J. Gero, J. Tadić, D. Helmig, S. Xie, E.J. Mlawer, T. Shippert, and M.S. Torn, “Observationally derived rise in methane surface forcing mediated by water vapour trends.” Nature Geoscience 11, 238 (2018). [DOI: 10.1038/s41561-018-0085-9]