There is convincing evidence that organic agriculture manages to keep more carbon stored in the soil. Of course, striving for a high percentage of organic matter in the soil is the basic premisse of organic agriculture, and the reason why it is called "organic." This lowers the amount of CO2 in the atmoshpere.
Water holding capacity
International studies in the USA and Germany have shown conclusively that organic soils have a better water holding capacity. This manifests itself in dry years, when organic soils give better yields than conventional soils. Conversely, when the water levels are high, organic soils offer much better protection against erosion and flooding.
Soils are the key to the climate solution
Recently the EU published the report "Soil - the hidden part of the climate cycle". The report shows that soils are by far the largest carbon stores on our planet that we can actually manage. Our soils are sequestring more carbon than the atmospere and all life forms together. And we can increase the amount of carbon that is stored in the soil, by turning to organic agriculture.
Greenhouse gasses are gassed that tend to heat up the atmosphere, because they absorb infrared radiation. The main greenhouse gasses are CO2 (carbon dioxide), CH4 (methane), and N2O (nitrous oxide, laughing gas). The greenhouse effect of methane is 4 times as strong as carbon dioxide, while nitrous oxide is 300 times as strong. Emission of nitrous oxide is mainly caused by production and use of artificial fertilizers, but also by the use of normal manure and by ploughing grassland.