Relative importance of thermal versus carbon dioxide induced warming from fossil-fuel combustion

Abstract:

The Earth is heated both when reduced carbon is oxidized to carbon dioxide and when outgoing longwave radiation is trapped by carbon dioxide in the atmosphere (CO₂ greenhouse effect). The purpose of this study is to improve our understanding of time scales and relative magnitudes of climate forcing increase over time from pulse, continuous, and historical CO₂ and thermal emissions. To estimate the amount of global warming that would be produced by thermal and CO₂ emissions from fossil fuel combustion, we calculate thermal emissions with thermal contents of fossil fuels and estimate CO₂ emissions with emission factors from Intergovernmental Panel on Climate Change (IPCC) AR5. We then use a schematic climate model mimicking Coupled Model Intercomparison Project Phase 5 to investigate the climate forcing and the time-integrated climate forcing. We show that, considered globally, direct thermal forcing from fossil fuel combustion is about 1.71% the radiative forcing from CO₂ that has accumulated in the atmosphere from past fossil fuel combustion. When a new power plant comes on line, the radiative forcing from the accumulation of released CO₂ exceeds the thermal emissions from the power plant in less than half a year (and about 3 months for coal plants). Due to the long lifetime of CO₂ in the atmosphere, CO₂ radiative forcing greatly overwhelms direct thermal forcing on longer time scales. Ultimately, the cumulative radiative forcing from the CO₂ exceeds the direct thermal forcing by a factor of ~100,000.