Global impacts of electrical means on global warming

In the context of rapidly advancing climate change, we need to reduce greenhouse gas emissions more aggressively. Globally, the main sources of emissions are electricity and heat (31%), agriculture (11%), transportation (15%), forestry (6%) and manufacturing (12%). Energy production of all types accounts for 72% of all emissions. Some of the IPCC's contenders for staying below 2°C by 2050 are more or less effective. Here we will evaluate the impact of the most important power generation tools.

CO2 emissions represent about 76% of total greenhouse gas emissions. Methane, mainly of agricultural origin, contributes to 16% of greenhouse gas emissions and nitrous oxide, mainly of industrial and agricultural origin, contributes to 6% of global emissions.

Water vapor is known to be the most abundant greenhouse gas on Earth, but the extent of its contribution to global warming has been debated, with no consensus being reached at present. Nevertheless, it is known that water vapor traps heat in the air, validating the gas's role as a key component of climate change. Andrew Dessler and colleagues at Texas A&M University in College Station have confirmed that the heat amplification effect of water vapor is strong enough to double the global warming caused by rising carbon dioxide levels in the atmosphere (Dessler 2008).

With new observations, scientists have experimentally confirmed what existing climate models had predicted theoretically. The research team used new data from the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite to accurately measure moisture in the lowest 18 kilometers of the atmosphere. This information was combined with global observations of temperature change, allowing the IPCC to build a complete picture of the interaction between water vapor, carbon dioxide, and other gases that warm the atmosphere.

Anthropogenic heat flux (AHF), refers to the heat dissipated by human activities (e.g., power generation, industry, transportation). Several works have explored its possible effect on the Earth's global climate system, some of them arguing that it could become a major cause of global warming (Chaisson 2008) or, at least, that it should be taken into account when allocating funding among competing energies (Cowern & Ahn 2008, Jacobson et al. 2009). Recent work ( Zhang & Caldeira 2015 , Firth et al. 2019 ,Jin et al. 2019 ) has shown that the global effect of HFA is currently negligible, especially when compared to the radiative forcing caused by greenhouse gas emissions such as CO2. We will explore whether this will remain valid in the future by calculating the AHF for some long-term energy projections. Indeed, since low-carbon energy sources such as nuclear power produce large amounts of heat, limiting global warming to below 2°C would be even more difficult than expected in the case where heat has a significant impact.

Finally we will see why some of the solutions such as nuclear power generate more greenhouse gas emissions than in the scientific analyses used by the IPCC.

Application for the French nuclear power :

Calculation of steam emissions

The combustion of fossil fuels, biofuels and biomass releases not only heat, but also water vapor. Water vapor is the result of a chemical reaction between the hydrogen in the fuel and the oxygen in the air. Coal, natural gas and nuclear power plants require cold water to recondense the hot steam that comes out of a steam turbine. This process results in significant evaporation of water from a cooling tower to the sky.

In the equation,

M = ECO2 x Am/(FCO2 x Gelec) (1)

where ECO2 is the global anthropogenic CO2 emission rate at equilibrium (gr eq CO2 /y) which gives an anthropogenic mixing ratio of CO2 in the atmosphere, FCO2 is the direct radiative forcing (W/m2 ) of CO2, Gelec is the global annual energy production of the technology (kWh/yr). Radiative forcing is the net increase (+) or decrease (-) in solar and thermal infrared radiation coming down to the top of the atmosphere.

ECO2 = XCO2C/TCO2

where XCO2 (in ppmv) is the anthropogenic mixing ratio giving the current CO2 radiative forcing, TCO2 is the lifetime of CO2 in the atmosphere: 110 years (Schwartz 2021) increasing. As for the anthropogenic moisture energy flux averaged over the world, it can be obtained from the water vapor flux per unit of energy (V, kg-H2 O/kWh) as follows

Am = V x Le x Gelec/(S x Ae) (2)

where V = 3L-H2 O/kWh is the amount of water converted to steam, Le = 2460 J/kg-H2O is the latent heat of evaporation, Gelec = 2,643 x 10^12 is the annual production (in this case from nuclear power), S = 31,536 x 10^7 seconds per year, and Ae = 5.092 x 10^14 m2 is the surface area of the Earth.

Combining equations (1) and (2), we obtain the global average CO2 e emissions per unit of energy due to a positive or negative water vapor flux resulting from an energy generator, in the following form

M = ECO2 x V x Le/(FCO2 x S x Ae) (3)

Am = 3 x 2460 x 2643*10^12 / (31,536*10^7) x (5092*10^14)

Am = 0.00092 W/m2

M = Am x V x Le / (Gelec x S x Ae) (4)

M = 0.00092 x 3 x 2460 / (2643*10^12 x 31,536*10^7 x 5098*10^14)

M = 1,21 gr eq CO2/kWh of water vapor

Calculation of heat

CO2 e emissions (g-CO2 e/kWh) due to anthropogenic heat flow are calculated as follows for all technologies (including negative heat flows due to solar and wind):

H = ECO2 x Ah/(FCO2 x Gelec) (5)

where Ah is the anthropogenic heat flux 0.47 W/m2 (Lu 2017) due to a heat source from electric power generation.

H = 1.57 gr eq CO2/ kWh

Opportunity cost calculation

Opportunity cost emissions are emissions from the baseline power system averaged over a defined period of time (e.g., 20 years or 100 years) due to two factors. The first factor is the longer time between planning and operation of one energy technology compared to another. The second factor is the longer downtime required to refurbish a technology at the end of its useful life when it is shorter than another technology (Jacobson, 2009).

For example, if plant A takes 4 years to plan and operate and plant B takes 10 years to plan and operate, the background network will emit pollution for 6 more years over 100 years with plant B than with plant A. The emissions during these additional 6 years are opportunity cost emissions.

These additional emissions include emissions of air pollutants affecting health and climate.

For the example I will take the reactor under construction in Flamanville whose first discussions began in 2002/2003, for a planned end of construction in 2023. That is 20 years. This is not very far from the average time of other reactors. I also chose to take the average life of the reactors stopped in 2021, that is to say 45 years and the time of stops for maintenance, refills, decennial visits, breakdowns,... is 3 years. While for wind power the construction time is 3 years and 1 month for downtime, which we calculate with,

ECOn = EBR,n - EBR,e

EBR,n = 105 x (20 + (100-20) x 3 / 45

EBR,n = 26,6 grCO2/kWh

EBR,e = 105 x (3 + (100 - 3) x 1 / 25

EBR,e = 7,2 grCO2/kWh

ECOn = 26,6 - 7,2

ECOn = 19.4 grCO2/kWh