The impact of internal climate variability on OH trends between 2005 and 2014

We show that ten-year Omega TOH trends are strongly affected by internal climate variability, as the spread of Omega TOH trends across the ensemble varies between 0.23%/year in Asia and 1.53%/year in South America. We train a fully connected neural network to emulate the Omega TOH simulated by the CESM2-WACCM6 model and combine it with satellite observations to interpret the role of OH chemical proxies. While the OH chemical proxies are subject to internal variability, the impact of internal variability on Omega TOH trends is primarily due to the meteorological parameters except for South America.

Forced trends in global mean Omega TOH do not unambiguously emerge from trends driven by internal variability over the 2005-2014 period. The observation-constrained Omega TOH presents opposite trends due to climate variability, resulting in varying conclusions on the attribution of OH to CH4 trends.