Greenhouse gas mitigation by agricultural intensification

Abstract

As efforts to mitigate climate change increase, there is a need to identify cost-effective ways to avoid emissions of greenhouse gases (GHGs). Agriculture is rightly recognized as a source of considerable emissions, with concomitant opportunities for mitigation. Although future agricultural productivity is critical, as it will shape emissions from conversion of native landscapes to food and biofuel crops, investment in agricultural research is rarely mentioned as a mitigation strategy. Here we estimate the net effect on GHG emissions of historical agricultural intensification between 1961 and 2005. We find that while emissions from factors such as fertilizer production and application have increased, the net effect of higher yields has avoided emissions of up to 161 gigatons of carbon (GtC) (590 GtCO(2)e) since 1961. We estimate that each dollar invested in agricultural yields has resulted in 68 fewer kgC (249 kgCO(2)e) emissions relative to 1961 technology ($14.74/tC, or approximately $4/tCO(2)e), avoiding 3.6 GtC (13.1 GtCO(2)e) per year. Our analysis indicates that investment in yield improvements compares favorably with other commonly proposed mitigation strategies. Further yield improvements should therefore be prominent among efforts to reduce future GHG emissions.

Fig. 1.

Regional and global trends in population (Upper Left), crop production (Upper Right), crop area (Lower Left), and fertilizer use (Lower Right), 1961–2005.

Fig. 2.

Comparison of trends in the RW and AW scenarios between 1961 and 2005. (Upper) Agricultural yield weighted by production, cropland area, fertilizer consumption, and population. (Lower) Annual GHG emissions broken down by source (see Methods). The land use change values, plotted in green, assume the same pattern of expansion by biome in the RW and AW scenarios, corresponding to a global average of 105 ± 26 tC/ha lost, including both biomass and soil organic carbon losses.

Fig. 3.

(Upper) Price per ton of avoided carbon emissions due to investment in yield improvements for the AW1 scenario. Plotted price values are estimates for the total global agricultural investment between 1961 and 2005 divided by the total calculated carbon equivalent emissions differences between the RW and AW scenarios (including fertilizer production, agricultural soil emissions, rice production, and land use change), calculated over a broad range of land carbon values and agricultural investment estimates. Contour lines show carbon prices. The plotted square gives the price of carbon if all carbon savings between the RW and AW1 scenarios are attributed to all agricultural R&D between 1961 and 2005. The plotted triangle gives the price of carbon assuming that 70% of R&D is relevant to productivity, and that 34% of yield improvements can be attributed to R&D. Error bars span ±20% for land carbon values. (Lower) Cost and potential carbon savings across various sectors as calculated in the present study (red points) and by the IPCC (36).