Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 meters above the ground. These climatic grids, however, fail to reflect conditions below vegetation canopies, where critical ecosystem functions are controlled and most species reside. Here we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0-5 and 5-15 cm depth. These maps were created by calculating the difference between in-situ measured soil temperature based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all of the world’s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding 2 m gridded air temperature, by up to 10°C (mean = 3.0°C ± 2.1°C), with substantial variation across biomes and seasons. Soils in cold and/or dry biomes are annually substantially warmer (3.6°C ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (0.7 ± 2.3°C). The observed substantial and biome-specific offsets underpin that the projected impacts of climate and climate change on biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here, are an important step towards mitigating that issue for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining global gaps in in-situ measured microclimate data towards and further enhance the spatiotemporal resolution of global soil temperature products for ecological applications