Estimates of seasonal variation in fossil fuel CO2 emissions

Seasonal variations are evident in the atmospheric CO₂ concentration, and attempts to understand the causes of the variations require an estimate of the seasonal pattern of the fossil fuel CO₂ source term. Estimates were made of CO₂ emissions resulting from fossil fuel combustion on a month-to-month basis for a recent typical year (1982). Twenty-one countries account for over 86% of the fossil fuel emissions. Monthly fuel consumption was used directly for those countries where such fuel data were available, and for the others (e.g., USSR and China) fuel use data were deduced from other factors.

Results indicate that CO₂ emissions from gas fuel use show the largest seasonal variation, from 6.2% of the annual total in July or August to over 11.8% of the annual total in January. Liquid and solid fuel use shows less variation, with summer fractions about 7.8% of annual and winter about 9.2% of annual. Seasonal patterns are consistent throughout the Northern Hemisphere which dominates the global totals. Based on data for 87% of the world’s fossil fuel CO₂ emissions, the highest release rate is 389.1 million tons of carbon in January and the lowest is 307.8 million tons of carbon in August.