Peatlands are important ecosystems that store approximately one third of terrestrial organic carbon. Non-growing season carbon fluxes significantly contribute to annual carbon budgets in peatlands, yet their response to climate change is poorly understood. Here, we investigate the governing environmental variables of non-growing season carbon emissions in a northern peatland. We develop a support-vector regression model using a continuous 13-year dataset of eddy covariance flux measurements from the Mer Blue Bog, Canada. We determine that only seven variables were needed to reproduce carbon fluxes, which were most sensitive to net radiation above the canopy, soil temperature, wind speed and soil moisture. We find that changes in soil temperature and photosynthesis drove changes in net carbon flux. Assessing net ecosystem carbon exchange under three representative concentration pathways, we project a 103% increase in peatland carbon loss by 2100 under a high emissions scenario. We suggest that peatland carbon losses constitute a strong positive climate feedback loop.

Climate change is a threat to the 500 Gt carbon stored in northern peatlands. As the region warms, the rise in mean temperature is more pronounced during the non-growing season (NGS, i.e., winter and parts of the shoulder seasons) when net ecosystem loss of carbon dioxide (CO2) occurs. Many studies have investigated the impacts of climate warming on NGS CO2 emissions, yet there is a lack of consistency amongst researchers in how the NGS period is defined. This complicates the interpretation of NGS CO2 emissions and hinders our understanding of seasonal drivers of key carbon exchange processes. Here, we analyze the impact of alternative definitions of the NGS for a peatland site with multiple years of CO2 flux records. Three climatic parameters were considered to define the NGS: air temperature, soil temperature, and snow cover. Our findings reveal positive correlations between estimates of the cumulative non-growing season net ecosystem CO2 exchange (NGS-NEE) and the length of the NGS for each alternative definition, with the greatest proportion of variability explained using snow cover (R 2 = 0.89, p < 0.001), followed by air temperature (R 2 = 0.79, p < 0.001) and soil temperature (R 2 = 0.54, p = 0.006). Using these correlations, we estimate average daily NGS CO2 emitted between 1.42 and 1.90 gCO2 m-2, depending on which NGS definition is used. Our results highlight the need to explicitly define the NGS based on available climatic parameters to account for regional climate and ecosystem variability.

The world’s cold regions are experiencing some of the fastest warming, especially during the winter and shoulder seasons. Recent studies have highlighted the significance of carbon dioxide (CO2) emissions during the non-growing season (NGS) to the annual carbon budgets of northern peatlands. Because of the positive feedback of soil microbial respiration to warming, a warmer NGS may be expected to alter the carbon balance of peatlands, which are estimated to store about one-third of global terrestrial organic carbon stocks. However, estimates of NGS net ecosystem CO2 exchange (NEE) remain highly uncertain. In this study, we determine key environmental variables affecting the NGS-NEE from a temperate peatland (Mer Bleue Bog; Ottawa, Canada) and predict future NGS-NEE under three climate scenarios (RCP2.6, RCP4.5, and RCP8.5) using a variable selection methodology, global sensitivity analysis, and data-driven model. The model successfully reproduces the observed NGS-NEE fluxes using only 7 variables, with NGS-NEE being most sensitive to changes in net radiation. Our projections estimate that mean NEE during the NGS could increase by up to 103% by the end of the 21st century; thus, reinforcing the urgent need for a comprehensive understanding of peatlands as evolving sources of atmospheric CO2 in a warming world.