Improved estimates of carbon dioxide emissions from drained peatlands support a reduction in emission factor

Under the United Nations Framework Convention on Climate Change, Annex 1 countries must report annual carbon dioxide (CO2) emissions from peatlands drained for extraction. However, the Tier 1 emission factor (EF) provided in the IPCC 2014 Wetland Supplement is based mainly on warm season data from a limited number of sites. Here we evaluate the current IPCC EF and revise it with newly published data. The updated EF is 2.46 +/- 0.25 t C ha-1 yr-1, a 12% reduction and a threefold decrease in the confidence interval compared to the current IPCC (2014) EF. We generate a Tier 3 EF, 1.4 +/- 0.25 t C ha-1 yr-1 for a typical extraction site in eastern Canada using numerical CoupModel that explicitly considers seasonality and interannual climatic variability, and suggest how to account for seasonality for the previously published EFs. This reduction has implications for comparing alternatives to peat-based growing substrates, the assessment of offsets, and possible punitive carbon taxes or cap-and-trade schemes. An assessment of peatlands drained for extraction indicates a 12% reduction in annual carbon dioxide emission relative to the emission factor provided in the IPCC 2014 Wetland Supplement and reduced uncertainty in emission factor, suggest a data compilation and numerical model simulations.