In their recent paper on how to avoid dangerous climate change, Y. Xu and V. Ramanathan propose strategies to keep global warming within 1.5°C by 2100 (relative to 1900). One strategy was to seriously reduce emissions of methane, which is estimated to be at least 84 times more potent than CO2 over a 20-year time horizon. Methane emissions come from a mix of natural and anthropogenic sources, very roughly summarized in the following table*:
In this post, I'm going to focus on wetlands. Home to methane-spewing microbes, wetlands are the largest source of methane emissions in the world. Wetlands are likely responsible for a 3% rise in atmospheric methane over the past decade, which appears to have tracked several years of heavy rains in the tropics, leading to a surge in wetlands and their resident microbes. What can we do about this natural phenomenon?
Turns out not all wetlands are created equal. For instance, saline wetlands are minor emitters of methane, because a substance in seawater limits methane production. It's the freshwater and low saline wetlands that are the major methane-emitting culprits. And many of these wetlands are not "natural" at all - humans have altered their salinity in the service of aquaculture, mosquito control, rice production, and wildfowl management. Re-salinating as many of these wetlands as we can through restoration of coastal ecosystems would put a real dent in global methane emissions. Luckily, a coordinated global effort is already on the case, thanks to the International Blue Carbon Initiative. Better water management of rice fields would reduce emissions as well. The US and China are already making progress on that front. It is only a matter of time before the rest of the rice growing world catches up.
Also, this just in: methane-eating microbes! Currently these beasties appear to prefer melting Antarctic ice sheets but perhaps they have warm-weather cousins yet to be discovered (or yet to be created).
--
* These percents are based on averaging estimates from several publications listed in a Wikipedia article, an approach I took because there does not yet appear to be a scientific consensus on the relative contribution of methane emitters. So many publications, so many different estimates! More recent methane emissions estimates appear to be lower for rice agriculture and higher for wetlands.
Next: Anthropogenic sources of methane: gas/oil, cows, and rice agriculture.
Reference:
Kroeger, K. D., Crooks, S., Moseman-Valtierra, S., & Tang, J. (2017). Restoring tides to reduce methane emissions in impounded wetlands: A new and potent Blue Carbon climate change intervention. Scientific Reports, 7, 11914. http://doi.org/10.1038/s41598-017-12138-4