Microclimate temperature variations from boreal forests to the tundra

•We found high thermal heterogeneity over boreal forest and tundra biomes.•Thermal differences were >15°C in soil and >30°C at near-surface in the tundra.•In boreal forests, thermal variability was link to canopy cover and water covers.•In tundra, thermal variability was linked to elevation, local topography, and snow.•The study design enables examining local impacts of climate change on northern ecosystems.