Interannual variation in methane emissions from tropical wetlands triggered by repeated El Niño Southern Oscillation

Abstract

Methane (CH ) emissions from tropical wetlands contribute 60%-80% of global natural wetland CH emissions. Decreased wetland CH emissions can act as a negative feedback mechanism for future climate warming and vice versa. The impact of the El Niño-Southern Oscillation (ENSO) on CH emissions from wetlands remains poorly quantified at both regional and global scales, and El Niño events are expected to become more severe based on climate models' projections. We use a process-based model of global wetland CH emissions to investigate the impacts of the ENSO on CH emissions in tropical wetlands for the period from 1950 to 2012. The results show that CH emissions from tropical wetlands respond strongly to repeated ENSO events, with negative anomalies occurring during El Niño periods and with positive anomalies occurring during La Niña periods. An approximately 8-month time lag was detected between tropical wetland CH emissions and ENSO events, which was caused by the combined time lag effects of ENSO events on precipitation and temperature over tropical wetlands. The ENSO can explain 49% of interannual variations for tropical wetland CH emissions. Furthermore, relative to neutral years, changes in temperature have much stronger effects on tropical wetland CH emissions than the changes in precipitation during ENSO periods. The occurrence of several El Niño events contributed to a lower decadal mean growth rate in atmospheric CH concentrations throughout the 1980s and 1990s and to stable atmospheric CH concentrations from 1999 to 2006, resulting in negative feedback to global warming.

Impact of El Niño–Southern Oscillation on the interannual variability of methane and tropospheric ozone

“…However, good overall agreement of model simulations with different observations, including the ability of the model to simulate the observed atmospheric responses to El Niño events (i.e. OEI change of 2.8 DU compared to 2.4 DU in Ziemke et al, 2010), provides confidence in model performance and results.…”

“…We have also assessed the capability of TOMCAT-GLOMAP to simulate observed responses to El Niño events. Ziemke et al (2010) derived an O 3 ENSO index using satellite observations, finding that for a +1 K change in the Niño 3.4 index, there was a 2.4 DU increase in the Ozone ENSO Index (OEI). In TOMCAT-GLOMAP, we calculate a 2.8 DU increase per +1 K in the Niño 3.4, indicating a slightly larger but comparable response to El Niño events.…”

“…Emissions from natural wetlands have been shown to be the dominant process, with emissions from fires and changes to the atmospheric sink also playing important roles (Bousquet et al, 2006;Chen and Prinn, 2006;Dlugokencky et al, 2011;Kirschke et al, 2013;McNorton et al, 2016aMcNorton et al, , 2018Corbett et al, 2017). These natural sources are climate sensitive, so interannual changes to temperature and precipitation affect the amount of CH 4 emitted into the atmosphere, as well as the spatial distribution (Zhu et al, 2017). A number of studies have found that biomass burning emissions are largely responsible for the IAV of carbon monoxide (CO) and also affect O 3 concentrations (Granier et al, 2000;; however, Szopa et al (2007) suggested that meteorology is a more important driver of IAV for CO, explaining 50 %-90 % of IAV.…”

“…Due to the wide-ranging effects of El Niño and varied sources of CH 4 , there are multiple factors which could trigger the increase in CH 4 growth rate. Chen and Prinn (2006) attributed the increase to anomalies in global wetland emissions; however, Zhu et al (2017) estimated that although 49 % of the interannual variation in wetland emissions can be explained by ENSO, wetland emissions were significantly lower during El Niño, including the 1997event. Conversely, Schaefer et al (2018 estimated that ENSO is responsible for up to 35 % of global CH 4 variability, but the effect of wetland and biomass burning emission changes are dwarfed by processes affecting the OH sink.…”

Impact of El Niño Southern Oscillation on the interannual variability of methane and tropospheric ozone

“…Emissions from natural wetlands have been shown to be the dominant process, with emissions from fires and changes to the atmospheric sink also playing important roles (Bousquet et al, 2006;Chen and Prinn, 2006;Dlugokencky et al, 2011;Kirschke et al, 2013;McNorton et al, 2016;Corbett et al, 2017). These natural sources are climate sensitive, so interannual changes to temperature and precipitation affect the amount of CH4 emitted into the atmosphere as well as the spatial distribution (Zhu et al, 2017). Studies have found that biomass burning emissions are largely responsible for the IAV of carbon monoxide (CO) and also affect O3 concentrations (Granier et al, 2000;Monks et al, 2012;.…”