Preprints
https://doi.org/10.5194/egusphere-2023-2550
https://doi.org/10.5194/egusphere-2023-2550
04 Dec 2023
 | 04 Dec 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Estimation of Canada’s methane emissions: inverse modelling analysis using the ECCC measurement network

Misa Ishizawa, Douglas Chan, Doug Worthy, Elton Chan, Felix Vogel, Joe R. Melton, and Vivek K. Arora

Abstract. Canada has major sources of atmospheric methane (CH4), with the world second-largest boreal wetland and the world fourth-largest natural gas production. However, Canada’s CH4 emissions remain uncertain among estimates. Better quantification and characterization of Canada’s CH4 emissions are critical for climate mitigation strategies. To improve our understanding of Canada’s CH4 emissions, we performed an ensemble regional inversion (2007–2017) constrained with the Environment and Climate Change Canada (ECCC) surface measurement network. The decadal CH4 estimates show no significant trend, unlike some studies that reported long-term trends. The total CH4 estimate is 17.4 (15.3–19.5) Tg CH4 year-1, partitioned into natural and anthropogenic sources, 10.8 (7.5–13.2) and 6.6 (6.2–7.8) Tg CH4 year-1, respectively. The estimated anthropogenic emission is higher than inventories, mainly in western Canada (with the fossil fuel industry). Furthermore, the results reveal notable spatiotemporal characteristics. First, the modelled gradients of atmospheric CH4 show improvement after inversion when compared to observations, implying the CH4 gradients could help verify the inversion results. Second, the seasonal variations show slow onset and late summer maximum, indicating wetland CH4 flux has hysteretic dependence on air temperature. Third, the boreal winter natural CH4 emissions, usually treated as negligible, appear quantifiable (≥ 20 % of annual emissions). Understanding winter emission is important for climate prediction, as the winter in Canada is warming faster than the summer. Fourth, the inter-annual variability in estimated CH4 emissions is positively correlated with summer air temperature anomalies. This could enhance Canada’s natural CH4 emission in the warming climate.

Misa Ishizawa, Douglas Chan, Doug Worthy, Elton Chan, Felix Vogel, Joe R. Melton, and Vivek K. Arora

Status: open (extended)

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  • RC1: 'Comment on egusphere-2023-2550', Anonymous Referee #1, 21 Feb 2024 reply
Misa Ishizawa, Douglas Chan, Doug Worthy, Elton Chan, Felix Vogel, Joe R. Melton, and Vivek K. Arora
Misa Ishizawa, Douglas Chan, Doug Worthy, Elton Chan, Felix Vogel, Joe R. Melton, and Vivek K. Arora

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Short summary
Methane (CH4) emissions in Canada for 2007–2017 were estimated using Canada’s surface Greenhouse Gas measurements. The estimated decadal emissions show no significant trend, but the uncertainty is reduced over time as more measurements became available. We find notable features in the CH4 emissions, such as a positive correlation with surface air temperature in summer. The measurement network across Canada could monitor future CH4 emission changes and compliance for climate mitigation goals.