The amount of carbon dioxide released from Australian savannah and grassland soils as temperatures rise may be lower than previously predicted, according to a study online in Nature Geoscience. Annual emissions of carbon dioxide from soil organic carbon are an order of magnitude greater than all human-made carbon dioxide emissions taken together, and are expected to increase as the Earth warms.

Johannes Lehmann and colleagues analysed soil samples stored in archives from hundreds of sites across Australia. According to their analyses, black carbon, which forms in wildfires, comprises a significant proportion of the total soil carbon. When these observation-based estimates of black carbon in soil were used in regional scale soil models, the amount of carbon dioxide predicted to be released from two Australian savannah regions under a 3?C warming scenario was 18.3% and 24.4% lower than previously calculated.

However, the team cautions that other responses to climate change, such as changing soil moisture and wildfire frequency, could affect the production and storage of black carbon in the soil.