Inconsistencies in SOC stocks (to 1 m depth) between observation-based (Northern Circumpolar Soil Carbon Database; www.bbcc.su.se/data/ncscd/) and baseline ESM estimates calculated from the mean values in four CMIP5 models (BCC-CSM1.1, CanESM2, MIROC-ESM, and GFDL-ESM2M)

<p><strong>Figure 1.</strong> Inconsistencies in SOC stocks (to 1 m depth) between observation-based (Northern Circumpolar Soil Carbon Database; <a href="http://www.bbcc.su.se/data/ncscd/" target="_blank">www.bbcc.su.se/data/ncscd/</a>) and baseline ESM estimates calculated from the mean values in four CMIP5 models (BCC-CSM1.1, CanESM2, MIROC-ESM, and GFDL-ESM2M). Brown (+ sign) identifies overpredictions by models compared to observation-based data; white shows tentative agreement; and blue (− sign) shows model under-predictions.</p> <p><strong>Abstract</strong></p> <p>The vast amount of organic carbon (OC) stored in soils of the northern circumpolar permafrost region is a potentially vulnerable component of the global carbon cycle. However, estimates of the quantity, decomposability, and combustibility of OC contained in permafrost-region soils remain highly uncertain, thereby limiting our ability to predict the release of greenhouse gases due to permafrost thawing. Substantial differences exist between empirical and modeling estimates of the quantity and distribution of permafrost-region soil OC, which contribute to large uncertainties in predictions of carbon–climate feedbacks under future warming. Here, we identify research challenges that constrain current assessments of the distribution and potential decomposability of soil OC stocks in the northern permafrost region and suggest priorities for future empirical and modeling studies to address these challenges.</p>