The photo is sourced from http://ksc.krasn.ru/

The air temperature is usually measured at meteorological stations, with closed and well-ventilated devices located in shade-free places up to two metres above the ground. However, these conditions are very different from the ones observed on the ground surface where most terrestrial species live and where basic ecological, biophysical and biochemical processes take place. To determine how big the difference between the two types of conditions is, scientists used nine thousand sensors to collect data about multi-year, year-round soil temperature measurements in sixty countries.

The results of the study showed that in cold and dry biomes (the sets of ecosystems of the same natural and climatic zone), such as the Tundra, subtropical deserts and boreal forests, the average annual temperature of an upper soil layer exceeded the air temperature by an average of four degrees. A different picture is characteristic for warm and humid biomes, including temperate forests and tropical savannahs, where the soil temperatures were, on average, one degree lower than the air temperatures. Scientists displayed the results of their observations on the global map where the blue colours indicate the soil temperature lower than the air one, and the red colours indicate, on the contrary, the soil warmer than the air.

The main conclusion drawn for the study was unevenness of soil heating with warming of the climate: one-degree increase in the air temperature will affect the temperature of the upper layers of the soil in hot biomes faster than in cold ones. This finding will have important implications for researching the ecosystem resilience. “Soil temperature rather than the air one better predicts such ecosystem functions as an annual growth of tree trunks, decomposition of organic matter and other aspects of the global carbon balance,” the Krasnoyarsk Science Center portal quotes Anatoly Prokushkin, the Laboratory Head of the Sukachev Forest Institute, SB RAS. “The use of soil temperature in correlation analysis or prognostic models could improve predictions of the climate impacts on physiology and behaviour of organisms, as well as on population and community dynamics and species distribution.”

The average global air temperature, so far, remains the key marker of climate change: according to the UN, in 2021, it exceeded the pre-industrial level by 1.11 degrees Celsius. According to the Intergovernmental Panel on Climate Change (IPCC), exceeding this threshold by 1.5 degrees Celsius is critical.