Large loss of CO 2 in winter observed across the northern permafrost region

Recent warming in the Arctic, which has been amplified during the winter1–3, greatly enhances microbial decomposition of soil organic matter and subsequent release of carbon dioxide (CO2)4. However, the amount of CO2 released in winteris not known and has not been well represented by ecosystem modelsor empirically based estimates5,6. Here we synthesize regional in situ observations of CO2 flux from Arctic and boreal soils to assess current and future wintercarbon losses from the northern permafrostdomain. We estimate a contemporary loss of 1,662 TgC per year from the permafrostregion during the winterseason (October–April). This loss is greater than the average growing seasoncarbon uptake for this region estimated from process models (−1,032 TgC per year). Extending model predictions to warmer conditions up to 2100 indicates that winterCO2 emissions will increase 17% under a moderate mitigation scenario— Representative Concentration Pathway4.5—and 41% under business-as-usual emissions scenario— Representative Concentration Pathway8.5. Our results provide a baseline for winterCO2 emissions from northern terrestrial regions and indicate that enhanced soil CO2 loss due to winterwarming may offset growing seasoncarbon uptake under future climatic conditions. Winterwarming in the Arctic will increase the CO2 flux from soils. A pan-Arctic analysis shows a current loss of 1,662 TgC per year over the winter, exceeding estimated carbon uptake in the growing season; projections suggest a 17% increase under RCP 4.5 and a 41% increase under RCP 8.5 by 2100.