When our article was
published (Sombroek et al. 1993) it was in the relative early days of concern
about global warming (the IPCC had only been established a couple of years
before in 1989). The Food and Agriculture Organization (FAO) of the United
Nations had other priorities at the time, focusing on food security and
technical and policy assistance to Ministries of Agriculture in developing
nations. Wim Sombroek, who had a keen interest in environmental issues had just
been appointed as new director for the Land and Water Division at FAO’s
Headquarters in Rome, Italy. Before his arrival, the Land and Water Division
had been known for their activities at field level in developing countries in
assisting in soil surveys, establishing irrigation schemes and giving
fertilizer advice. The division had also built up a solid reputation in applied
research (crop water requirements), pure methodology development (the Framework
for Land Evaluation), and global information products in the field of soils
(The FAO/UNESCO Soil Map of the World). The previous director, Graham Higgins,
had inspired the Agro-ecological Zones methodology that determined agricultural
production potentials in the developing world. Wim Sombroek had started his
career in FAO as a junior expert in a FAO/UNESCO team for forestry research and
animal husbandry, based in Belem, Brazil. On the basis of this experience he
prepared a PhD-thesis on ‘‘Amazon soils’’, a subject that would remain near his
heart throughout his career. Afterwards he worked in several UNDP/FAO supported
soil projects, notably in Uruguay and Nigeria. He had gone on from there to
become the project manager of the Kenya Soil Survey between 1972 and 1978 where
he laid the basis for the SOTER (Soil and Terrain Database) approach to soil
mapping. In 1978 he became the Secretary General of the International Society
of Soil Science (ISSS, now IUSS) and the director of the International Soil
Information Center (ISRIC) until 1991. In a discussion with the Editor of Ambio
just after his appointment, Wim saw an opportunity to further his research
findings in the highly fertile Terra Preta de Indio soils of the Amazon Basin.
The high carbon content in this region was attributed to the deliberate
addition of charcoallike materials over thousands of years by the prehistoric
local inhabitants as well as by long-term mulching and frequent burning
practices. To place the research in a wider global warming context, I was
called in to use the FAO/ UNESCO Soil Map of the World as a basis for the
calculation of the global soil organic carbon pool. At the time I had only
recently joined FAO’s headquarter after having worked in FAO soil survey
projects in Sudan, the Philippines, Algeria, Tanzania and Botswana (where our
project had finalized the soil map, scale 1:1 000 000). As a FAO technical
officer I had always been fascinated in global soil studies and at the time I
was working on the digitizing the world soil map (a product that would be released
in 1995) and associated interpretations. The third scientist to assist with the
article was Axel Hebel, a German soil scientist who had also recently joined
FAO as an associate expert. The rapid evolution of GIS technology proved to be
a great assistance for the estimation of soil properties, but the limited
availability of readily available soil profile data (in particular soil carbon)
proved to be a significant obstacle. In the end, we estimated the soil carbon
content of the 26 FAO soil groups based on analytical data for only 400 soil
profiles. We were well aware that this is a very low statistical basis to
extrapolate results for about 6000 soil mapping units. In comparison more than
21 000 soil profiles were analyzed recently by International Soil Reference and
Information Centre (ISRIC) for the Harmonized World Soil Database.