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Published online 2 October 2018
An overlooked greenhouse gas effect of methane is surprisingly strong over desert regions, including the Sahara and Arabia.
The atmosphere of Jupiter has helped reveal a surprisingly large and regionally variable effect of atmospheric methane on Earth. The finding is especially relevant to the skies above desert regions such as the Sahara, the Arabian Peninsula and the Australian outback.
Climatologists and policy-makers may need to take note of the discovery when considering the effects of methane released by the oil industry. It may give a boost to initiatives aimed at reducing the release of methane and other greenhouse gases by the oil industry.
Researchers, led by William Collins at Lawrence Berkeley National Laboratory in California, explored how methane traps energy in the atmosphere by absorbing ‘near-infrared’ shortwave solar radiation.
“Methane’s interaction with this shortwave light is very complicated,” says Earth sciences researcher Daniel Feldman of the Berkeley team. He explains that the limitations of studies in laboratory conditions led the researchers to look at data previously gathered from the “natural laboratories” of Jupiter and of Saturn’s moon Titan. These systems contain thousands of times more methane than the Earth’s atmosphere, and reveal information about its energy absorption through much longer path-lengths than can be obtained in any lab.
Combining the insights from space science with the lab-based observations allowed the researchers to develop an empirical model that contains all methane absorption features. Applying their new understanding to model the effects of methane across the globe produced an intriguing surprise. The warming effect of methane driven by shortwave radiation was up to ten times stronger above desert regions, especially the Sahara and Arabian Peninsula, compared to elsewhere across the globe. “Prior to this study, we weren’t expecting to see strongly varying regional patterns,” says Feldman.
The research offers three key explanations for the surprising regional effect: increased sunlight, high surface reflectivity, and the dryness of the atmosphere.
Feldman emphasizes the need to include this newfound significance of methane in climate models used globally and locally. He points out that the consequences are not restricted to direct temperature rises, but also involve effects on air circulation patterns.
“Utilizing the observations from Jupiter is very ingenious,” says Georgiy Stenchikov, head of the atmospheric and climate modelling research group at King Abdullah University of Science and Technology in Saudi Arabia, who was not involved in the study. “Including additional methane heating might be important to correctly simulate processes in the region,” he adds.
Collins, W. D., Feldman, D. R., Kuo, C. & Nguyen N. H. Large regional shortwave forcing by anthropogenic methane informed by Jovian observations. Sci. Adv. 4, eaas9593 (2018).