Abstract: •Soils contain 1062 Pg organic C (SOC) in 0-1 m depth based on the adjusted Harmonized World Soil Database. Different estimates of bulk density of Histosols cause an uncertainty in the range of -56/+180 Pg. We also report the frequency distribution of SOC stocks by continent, wetland type, and permafrost type. Using additional estimates for frozen and deeper soils, global soils are estimated to contain 1325 Pg SOC in 0-1m and ca. 3000 Pg, including deeper layers. The global soil organic carbon (SOC) mass is relevant for the carbon cycle budget and thus atmospheric carbon concentrations. We review current estimates of SOC stocks and mass (stock × area) in wetlands, permafrost and tropical regions and the world in the upper 1 m of soil. The Harmonized World Soil Database (HWSD) v.1.2 provides one of the most recent and coherent global data sets of SOC, giving a total mass of 2476 Pg when using the original values for bulk density. Adjusting the HWSD’s bulk density (BD) of soil high in organic carbon results in a mass of 1230 Pg, and additionally setting the BD of Histosols to 0.1 g cm−3 (typical of peat soils), results in a mass of 1062 Pg. The uncertainty in BD of Histosols alone introduces a range of −56 to +180 Pg C into the estimate of global SOC mass in the top 1 m, larger than estimates of global soil respiration. We report the spatial distribution of SOC stocks per 0.5 arcminutes; the areal masses of SOC; and the quantiles of SOC stocks by continents, wetland types, and permafrost types. Depending on the definition of “wetland”, wetland soils contain between 82 and 158 Pg SOC. With more detailed estimates for permafrost from the Northern Circumpolar Soil Carbon Database (496 Pg SOC) and tropical peatland carbon incorporated, global soils contain 1325 Pg SOC in the upper 1 m, including 421 Pg in tropical soils, whereof 40 Pg occurs in tropical wetlands. Global SOC amounts to just under 3000 Pg when estimates for deeper soil layers are included. Variability in estimates is due to variation in definitions of soil units, differences in soil property databases, scarcity of information about soil carbon at depths > 1 m in peatlands, and variation in definitions of “peatland”.

Abstract: The mid-term meeting was held in Sassari, Sardinia, 1-4 April 2014. The meeting was attended by 120 researchers and stakeholders from 16 countries (Fig. 1). After a day of looking back on the achievements during the first two years and presenting results to stakeholders, researchers focused on fine-tuning the planning of remaining work for the project till May 2015 and preparations for a follow-up project (MACSUR2) till May 2017. On an excursion, scientists and stakeholders visited farms in the Oristano region, one of the regional case studies of MACSUR. The meeting was a unique opportunity in this pan-European project for discussing in person common issues with and among stakeholders of different regions and how to approach the impact of climate change to producing food in Europe in a world with a growing population. A report in La Nueva Sardegna  highlighted the conference. Excursion: dairy sheep farm “Su Pranu” (Siamanna), dairy cattle farm “Sardo Farm” (Arborea), Arborea Cooperative Recordings of the presentations are available on YouTube: https://www.youtube.com/channel/UCrjoXlUIJNBW8cWOgh0_g The presentations are available on the conference website: http://ocs.macsur.eu/index.php/Hub/Mid-term/schedConf/presentations Short papers derived from the presentations are available on the conference website and in FACCE MACSUR Reports vol 5. The food consumed during lunches at the conference originated mostly from the Oristano region. Remaining food in good condition was donated to a charity organisation for needy people. Fig. 1. Number of participants per country.