There are very few historical CO emission estimates available. USA/NAPET presents estimates for the USA since 1940 (36 ktons C), with 5 year intervals to 1990 (39 ktons C), with a peak in the 1970s (almost 50 ktons C). IIASA estimated the global CO emission for 1990 to be 492 ktons C, EDGAR 487 ktons C.
The major sources in 1990 of carbon monoxide were agricultural waste burning (21%), savannah burning (18%) and deforestation (11%; Olivier et al. 1996). Other important sources are road transport (21%) and the use of biofuels (19%). Most important regions who contribute to the total amount of carbon monoxide are located in Africa (savannah burning). According to EDGAR they emitted 25% of the global total, followed by Latin America (15%), China (11%) and India (11%).