Interannual fires as a source for subarctic summer decadal climate variability mediated by permafrost thawing

Abstract Climate model simulations run under the Coupled Model Intercomparison Project Phase 6 (CMIP6) use an inhomogeneous biomass burning aerosol (BBA) emission dataset, which exhibits pronounced interannual variability from 1997–2014 due to infusion of satellite data. Using Community Earth System version 2 Large Ensemble (CESM2-LE) with original and smoothed CMIP6 BBA forcings, we show that data inhomogeneity causes spurious decadal subarctic land warming. During years reduced concentrations, increased solar radiation can trigger abrupt permafrost thawing, soil water drainage, upper drying, subsequent surface This slow process, is further amplified by nonlinear cloud-aerosol interactions, cannot be completely offset during fluxes, thereby reddening temperature spectra in response large-amplitude forcing. More generally, our CESM2 experiments identify a pathway for generating high latitudes, involving shortwave forcing responses.