Professor Pete Smith is Professor of Soils and Global Change in the School of Biological Sciences at the University of Aberdeen. He is an internationally recognised expert in soil carbon sequestration and agricultural greenhouse gas mitigation, and has contributed to many international (UK, European and global) expert working groups in this area.

Agricultural lands occupy 37% of the Earth’s land surface. Agriculture accounts for 52% and 84% of global anthropogenic methane and nitrous oxide emissions. Agricultural soils may also act as a sink or source for carbon dioxide (CO₂), but the net flux is small. Many agricultural practices can potentially mitigate greenhouse gas (GHG) emissions, the most prominent of which are improved cropland and grazing land management and restoration of degraded lands and cultivated organic soils. Lower, but still significant mitigation potential is provided by water and rice management, set-aside, land use change and agroforestry, livestock management and manure management. The global technical mitigation potential from agriculture (excluding fossil fuel offsets from biomass) by 2030, considering all gases, is estimated to be ~5500-6000 megatonnes (Mt) CO₂-eq. yr^-1, with economic potentials of ~1500-1600, 2500-2700, and 4000-4300 Mt CO₂-eq. yr^-1 at carbon prices of up to 20, up to 50 and up to 100 US$ t CO₂-eq.^-1, respectively. In addition, GHG emissions could be reduced by substitution of fossil fuels for energy production by agricultural feed stocks (e.g. crop residues, dung, dedicated energy crops). The economic mitigation potential of biomass energy from agriculture is estimated to be 70-1260 Mt CO₂-eq. yr-1 at up to 20 USD t CO₂-eq.^-1, and 560-2320 Mt CO₂-eq. yr^-1 at up to 50 USD t CO₂-eq. There are no estimates for the additional potential from top down models at carbon prices up to 100 USD t CO₂-eq.^-1, but the estimate for prices above 100 USD t CO₂-eq.^-1 is 2720 Mt CO₂-eq. yr^-1. These potentials represent mitigation of 5-80%, and 20-90% of all other agricultural mitigation measures combined, at carbon prices of up to 20, and up to50 USD t CO₂-eq.^-1, respectively.

Status of agriculture

Technological developments have allowed remarkable progress in agricultural output per unit of land, increasing per-capita food availability despite a consistent decline in per-capita agricultural land area. However, progress has been uneven across the world with rural poverty and malnutrition remaining in some countries. The share of animal products in the diet has progressively increased in developing countries, whilst remaining constant in the developed world.

Production of food and fiber has more than kept pace with the sharp increase in demand in a more populated world, so that the global average daily availability of calories per-capita has increased, though with regional exceptions. However, this growth has been at the expense of increasing pressure on the environment and dwindling natural resources, and has not solved problems of food security and widespread child malnutrition in poor countries.

The absolute area of global arable land has grown to about 1400 million hectares (Mha), an overall increase of 8% since the 1960s (5% decrease in developed countries, and 22% increase in developing countries). This trend is expected to continue into the future, with a projected additional 500 Mha converted to agriculture from 1997-2020, mostly in Latin America and Sub-Saharan Africa.

Economic growth and changing lifestyles in some developing countries are causing a growing demand for meat and dairy products. From 1967-1997, meat demand in developing countries rose from 11 to 24 kg per capita per year, achieving an annual growth rate of more than 5% by the end of that period. Further increases in global meat demand (about 60% by 2020) are projected, mostly in developing regions such as South and Southeast Asia, and Sub-Saharan Africa.

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Main photo credit: Natural Resources Conservation Service