LONDON, March 23 -- Soil, river sediment and dead vegetation lock away more planet-warming CO2 caused by humanity than trees, said a new study published Thursday, challenging long-held assumptions about how Earth stores carbon.

The discovery would be "crucial for shaping future climate" policies for reducing greenhouse gas emissions and improving the capture and storage of carbon dioxide from the atmosphere, the study's authors said.

About one-third of CO2 released by human activities is stored in land-based carbon sinks like forests, which along with oceans help slow global warming by absorbing excess heat-trapping emissions.

But forests are under threat, and their capacity to soak up CO2 has been diminished due to global warming, dis...