Using an Inverse Model to Reconcile Differences in Simulated and Observed Global Ethane Concentrations and Trends Between 2008 and 2014

Abstract We use a global model, TOMCAT, and an inverse model, INVICAT, to estimate emissions of ethane (C 2 H 6 ) between 2008 and 2014 by assimilating surface flask observations. We find that baseline global emissions in 2008 need to increase by a factor of 2.04–2.11 in order for the model to capture C 2 H 6 observations, indicating large biases in current emission inventories. Most of this increase occurs over North America and Eurasia, with temperate North American emissions accounting for 23–26% of the total global emission increase and temperate Eurasian emissions accounting for 35–37%. Further to this, recent peer‐reviewed analysis of long‐term observational records shows an increase in C 2 H 6 in the Northern Hemisphere since ~2009. Our results indicate that annual global emissions of C 2 H 6 have increased at a rate of 0.27 ± 0.54–0.33 ± 0.44 Tg/yr 2 between 2008 and 2014. A statistically significant positive trend of 0.20 ± 0.11–0.24 ± 0.13 Tg/yr 2 ( p ≤ 0.01) is found in temperate North America, resulting in emissions that are 31–32% larger in 2014 than in 2008. Our results corroborate previous studies' conclusions that a rapid increase in oil and natural gas production in United States over this time period is likely a large driver of the change in emissions.