No significant increase in long‐term CH₄ emissions on North Slope of Alaska despite significant increase in air temperature

Abstract

Continuous measurements of atmospheric methane (CH4) mole fractions measured by NOAA's Global Greenhouse Gas Reference Network in Barrow, AK (BRW), show strong enhancements above background values when winds come from the land sector from July to December from 1986 to 2015, indicating that emissions from arctic tundra continue through autumn and into early winter. Twenty‐nine years of measurements show little change in seasonal mean land sector CH4 enhancements, despite an increase in annual mean temperatures of 1.2 ± 0.8°C/decade (2σ). The record does reveal small increases in CH4 enhancements in November and December after 2010 due to increased late‐season emissions. The lack of significant long‐term trends suggests that more complex biogeochemical processes are counteracting the observed short‐term (monthly) temperature sensitivity of 5.0 ± 3.6 ppb CH4/°C. Our results suggest that even the observed short‐term temperature sensitivity from the Arctic will have little impact on the global atmospheric CH4 budget in the long term if future trajectories evolve with the same temperature sensitivity.

Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska

“…Overall, our results are consistent with tall and eddy-covariance tower studies (e.g. Karion et al, 2016;Zona et al, 2016;Sweeney et al, 2016) and provide observational evidence that region-wide CH 4 flux may be, on average, as high as 5 mg m −2 d −1 in the colder months of April and November, also consistent with previous studies on the North Slope (Zona et al, 2016) and interior of Alaska.…”

“…As our observations do not extend throughout the colder months, we do not provide annual budget estimates since other studies have found that significant emissions of CH 4 are observed in the shoulder and cold seasons (Zona et al, 2016;Sweeney et al, 2016;Karion et al, 2016).…”

“…This lack of trend could potentially be related to methanogen community structure in the Arctic, as recent microbiological research has found that communities from Arctic soils that were incubated at lower temperatures were insensitive to substrate manipulations, indicating that Arctic methanogens may not be sensitive to the addition of new labile carbon from thawing permafrost (Blake et al, 2015). While it is true that local-scale permafrost degradation patterns such as thermokarsts can result in local CH 4 fluxes of > 100 mg m −2 d −1 (Johnston et al, 2014), multidecadal studies such as Sweeney et al (2016) suggest that at a regional scale, CH 4 fluxes in Alaska have been stable.…”

The coming thaw

“…A multi-century timescale for permafrost feedbacks is consistent with current projections and expert assessments, which suggest little role for permafrost carbon release in twenty-first century climate change 5,6 . Instead, the degradation of permafrost and carbon release is expected to ramp up throughout the twenty-first and twenty-second centuries.…”

“…However, the rate of conversion of this ancient carbon to methane has not measurably increased over the sixty-year study period. This finding is backed up by satellite studies of methane emissions as well as methane inventories, none of which suggest substantial increases in methane emissions from the Arctic tundra [5][6][7] .…”