3.1 Instantaneous Pulse Emissions From Fossil Fuel Combustion

First, we consider instantaneous pulse emissions from fossil fuel combustion, relevant to the combustion of a small mass of coal, oil, or gas. The warming from thermal energy production occurs when a fossil fuel undergoes combustion, whereas warming from the emitted CO 2 continues for the lifetime of CO 2 in the atmosphere and can last thousands of years [Archer et al., 2009]. There are three major types of fossil fuel: coal, oil, and natural gas. Each fuel differs in its thermal and CO 2 emissions per unit mass. To compare these fuels, we consider scenarios releasing the same amount of thermal energy but differing amounts of CO 2 . We first consider the case of climate forcing from pulse combustion of fossil fuels (e.g., burning a single lump of coal). We consider thermal emissions and radiative forcing to have approximately equivalent effect on the climate system [Hansen et al., 1997] and refer to them collectively using the term “climate forcing,” We recognize that the geographic distribution of a forcing can have consequences for the resulting climate change [G. J. Zhang et al., 2013; X. Zhang et al., 2013] and that the effective radiative forcing can differ for different forcing factors with the same nominal climate forcing [IPCC, 2013], so results obtained here should be interpreted as approximate.

Thermal emissions from fossil fuel combustion provide a pulse of warming, but the resulting CO 2 ‐induced warming persists for many centuries or longer. Within a few months, the time‐integrated CO 2 ‐warming effect is greater than the direct thermal warming influence of an instantaneous pulse fossil fuel combustion. The time series of climate forcing (ΔF) resulting from the instantaneous pulse combustion of 1 EJ of coal, oil, or gas is shown in Figure 1a. This figure shows that radiative forcing from atmospheric CO 2 decreases as the CO 2 is absorbed by the oceans and land biosphere. At time 0, CO 2 forcings are 0.209, 0.162, and 0.124 mW/m2 per EJ for coal, oil, and gas, respectively. Figure 1b shows, for instantaneous pulse combustion of fuel at time 0, the time‐integrated global radiative forcing from the CO 2 released (IntF CO2 ) divided by the amount of heat released upon combustion (IntF thermal ). The time‐integrated radiative forcing from CO 2 released upon combustion exceeds the amount of heat released upon combustion after 0.093 years (~34 days), 0.122 years (~45 days), and 0.161 years (~59 days) for coal, oil, and gas, respectively. After 1 year, the integrated CO 2 radiative forcing (IntF CO2 ) exceeds the thermal forcing by factors of 3.91, 3.03, and 2.32 for coal, oil, and gas, respectively; after 100 years, these values increase to 179, 139, and 106 years, respectively; and after 1000 years, they are 1047, 811, and 621, respectively (Figure 1b). As discussed below, ultimately, the warming induced by CO 2 over its lifetime in the atmosphere would exceed the warming from direct combustion by a factor of 100,000 or more.

Figure 1 Open in figure viewer PowerPoint 2 forcing response for pulse combustion and (b) ratios of time‐integrated CO 2 forcing (IntF CO2 ) to time‐integrated thermal forcing (IntF thermal ). IntF thermal is the heat of combustion. The inset in Figure 2 (i.e., the amount of energy that the CO 2 has prevented from escaping to space) to exceed the thermal forcing from the combustion that generated CO 2 for coal, oil, and gas, respectively. Results for instantaneous pulse emissions from burning coal, oil, and gas at time 0. (a) COforcing response for pulse combustion and (b) ratios of time‐integrated COforcing (IntF) to time‐integrated thermal forcing (IntF). IntFis the heat of combustion. The inset in Figure 1 b shows that it takes 0.093 years (~34 days), 0.122 years (~45 days), and 0.161 years (~59 days) for the integrated radiative forcing from CO(i.e., the amount of energy that the COhas prevented from escaping to space) to exceed the thermal forcing from the combustion that generated COfor coal, oil, and gas, respectively.