Editing IPCC:AR6/WGI/Chapter-2 (section)

===== 2.2.3.2.2 Methane (CH <sub>4</sub> ) =====

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CH <sub>4</sub> concentrations over the past 110 kyr are higher in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH), but closely correlated on centennial and millennial timescales ( [[#Buizert--2015|Buizert et al., 2015]] ). On glacial to interglacial cycles, approximately 450 ppb oscillations in CH <sub>4</sub> concentrations have occurred ( [[#Loulergue--2008|Loulergue et al., 2008]] ). On millennial timescales, most rapid climate changes observed in Greenland and other regions are coincident with rapid CH <sub>4</sub> changes ( [[#Buizert--2015|Buizert et al., 2015]] ; [[#Rhodes--2015|Rhodes et al., 2015]] , 2017). The variability of CH <sub>4</sub> on centennial timescales during the early Holocene does not significantly differ from that of the late Holocene prior to about 1850 ( [[#Rhodes--2013|Rhodes et al., 2013]] ; [[#Yang--2017|Yang et al., 2017]] ). The LGM concentration was 390.5 ± 6.0 ppb ( [[#Kageyama--2017|Kageyama et al., 2017]] ). The global mean concentrations during 0–1850 CE varied between 625 and 807 ppb. High-resolution ice core records from Antarctica and Greenland exhibit the same trends with an inter-polar difference of 36–47 ppb ( [[#Sapart--2012|Sapart et al., 2012]] ; L. [[#Mitchell--2013|]] [[#Mitchell--2013|Mitchell et al., 2013]] ). There is a long-term positive trend of about 0.5 ppb per decade during the CE until 1750 CE. The most rapid CH <sub>4</sub> changes prior to industrialization were as large as 30–50 ppb on multi-decadal timescales. Global mean CH <sub>4</sub> concentrations estimated from Antarctic and Greenland ice cores are 729.2 ± 9.4 ppb in 1750 and 807.6 ± 13.8 ppb in 1850 (L. [[#Mitchell--2013|]] [[#Mitchell--2013|Mitchell et al., 2013]] ).

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