The depiction of farming's greenhouse-gas footprint (estimated at 30.9% of total emissions) is derived from a 2007 report that used data from 2004 (Nature 479, 279; 2011). But relative estimates of emissions from different sources have altered appreciably since then, largely because fossil-fuel usage and cement production for building have both escalated.

In 2000–07, carbon dioxide emissions due to land-use changes were 1.1 petagram carbon equivalents (Pg C) per year and emissions from fossil-fuel usage and cement production accounted for 7.6 Pg C per year (Y. Pan et al. Science 333, 988–993; 2011). The contribution from land-use changes was therefore 12.6% of carbon dioxide emissions over this period. Emissions of methane, nitrous oxide and fluorine-containing gases were about 3.1 Pg C per year, so land-use changes contributed less than 10% of total greenhouse-gas emissions.

Carbon dioxide emissions from fossil-fuel burning and cement production went up to about 9.1 Pg C in 2010. Assuming that the emissions from land-use changes were the same as in 2000–07 and that the carbon-equivalent contributions of methane, nitrous oxide and fluorine-containing gases were the same as in 2004, land-use changes would have accounted for only about 8% of total emissions last year.

Although the increase in emissions from fossil-fuel usage and cement production is well documented, estimates of emissions from land-use changes remain uncertain. But they are unlikely to be as high as the earlier data might indicate.