Regenerating the soil carbon sponge is our greatest point of leverage for salvaging the planet from the point of existential climate crisis. “Sponge” refers to the quality of a biologically active soil with high organic matter content to have lots of pore space for water absorption. Jehne states that every additional gram of soil carbon allows the soil to hold 8 additional grams of water. He emphasizes the soil sponge concept because it is the driver of healthy ecosystems, and also within our control to repair and regenerate.
Jehne explains that an average of 342 W/m2 of incident solar radiation enters the troposphere while just 339 W/m2 is reflected back into space due to the greenhouse effect [Jehne 2018: 19:00 min]. This leaves a continuous energy balance of 3 W/m2 heating up the planet. Of the solar radiation returning to space, 24% is released through latent heat fluxes from evapotranspiration [Jehne 2018: 1:34:15]. However, due to land use change, there is 50% less transpiration on Earth than there was some 8,000 years ago. Jehne estimates that increasing transpiration by only 5% would be enough to offset the 3 W/m2 surplus solar energy [Jehne 2018: 1:34:50].
Increasing transpiration is achieved by increasing vegetation cover, which in turn is achieved by regenerating the soil sponge. Jehne explains that conventional agriculture has employed techniques (such as burning, cultivating/tilling, applying fertilizer and pesticides, and use of irrigation and fallow) that quickly oxidize the carbon fixed by plants through photosynthesis. By contrast, regenerative agriculture builds up the soil carbon sponge by facilitating the ecological processes that create stable soil carbon and limit organic matter breakdown.
In addition to the cooling effect from the latent heat flux, transpiration also provides the moisture needed for cloud formation. Jehne states that a 2% increase in cloud cover, given its high albedo, is also enough to reflect the excess 3 W/m2 solar radiation that is otherwise absorbed on Earth [Jehne 2018: 1:39:25]. Furthermore, bacteria released from ecosystems serve as the most effective precipitation nuclei for making rain.
Jehne, Walter, 2018, New climate solutions, water cycles and the soil carbon sponge. Publ. by Biodiversity for a Livable Climate. Retrieved 22 July 2018 from https://www.youtube.com/watch?v=vHw5I_fclkc.
 Precipitation nuclei are tiny particles (including ice crystals, salts and bacteria) upon which micro-droplets of water in clouds coalesce into raindrops [Jehne 2018: 1:40:00].