University:
Boston University
Course:
CAS BI 303 | Evolutionary Ecology
Academic year:

2022
Views:

341

Pages:

11
Author:

ff4lecyzr

The Global Warming Potential is Inconsistent with the Physics of Climate Change and Misrepresents the Effects of Policy Interventions METHANE AS AN ENERGY SOURCE AND A GREENHOUSE GAS SUMMARY: Methane, the primary component of natural gas, is both a useful primary source of energy and a powerful greenhouse gas. It is as important as carbon dioxide in determining whether we meet our 2050 climate goals. --------------- Natural gas (blue bars) is the most versatile source of primary energy in the US energy system, serving power, residential, commercial, and industrial sectors. Natural gas plays a unique role in energy storage. Every winter it feeds about 500 terawatthours of energy into power and heating systems. There is no other energy storage system that has anywhere near this capability, in overall capacity and ability to store energy for seasonal use. The primary constituent (90-95%) of pipeline grade natural gas is methane, which when emitted directly to the atmosphere is a powerful greenhouse gas. Globally, about half of methane emissions are from natural sources (green segments) and the other half are anthropogenic (other colors). Methane is 120 times more powerful as a greenhouse gas than carbon dioxide, on a perkilogram basis. However, the global annual mass of fossil carbon dioxide emissions is 100 times greater than the global annual mass of anthropogenic methane emissions. Therefore, the prompt warming effect of the two gases are comparable. The graph shows the temperature effect of 20 years emissions of fossil carbon dioxide at the current global rate (black) compared to the effect of 20 years of emissions of anthropogenic methane at the current global rate (red). Methane emission reductions are the quickest way to slow global warming. Methane breaks down in the atmosphere with a time constant of about 12 years, whereas carbon dioxide has an atmospheric lifetime of centuries. Therefore, once methane is reduced, temperature effects are prompt. This plot shows the effect of reducing carbon dioxide emissions (blue) or methane emissions (red), starting in 2012. THE GLOBAL WARMING POTENTIAL AND THE CO2-EQ METHODOLOGY SUMMARY: The Global Warming Potential (GWP) underlies the CO2-equivalent methodology, used in international climate agreements to harmonize the effects of diverse greenhouse gases on climate change. However, GWP suffers from major conceptual problems, and has been criticized by many, including the climate scientists who introduced it in the First Assessment Report of the IPCC. ------------------- The Global Warming Potential (GWP) puts emissions of diverse greenhouse gases on a single CO2-equivalent scale. This method has been used in international agreements to harmonize the nationally determined contributions of nations which promise to limit emissions of greenhouse gases other than carbon dioxide. There is no intention here to suggest this system be changed. However, in selecting policy instruments to actually mitigate global climate change, the CO2-eq method and the global warming potentials on which it is based can be deceptive. The US Greenhouse Gas Inventory published by the Environmental Protection Agency uses GWP to compare the contributions of the various greenhouse gases to climate change. This chart suggests that carbon dioxide is the dominant contributor. This is deceptively oversimplified. See page 8, where it is shown that methane is an equal contributor to prompt temperature increases. The Global Warming Potential of methane is the ratio of two integrals. The numerator is the integral over time of the radiative forcing due to a unit mass of methane emitted to the atmosphere at t=0. The integrand is shown at the lower left. Dimensions are incident power per square meter per gram. Methane is oxidized and removed from the atmosphere with a time constant of 12.4 years. The denominator is the analgous quantity for carbon dioxide, the integrand being shown on the lower right. Atmospheric carbon dioxide is characterized by a multiexponential decay, with the longest time constants on the order of centuries. The upper bound of both integrals, T, is a relevant horizon time. T is often selected to be 20 years or 100 years. The integrations of GWP numerator and denominator are shown on the upper left and upper right. The vertical axis dimensions are cumulative energy per square meter per gram. The horizontal axis is the upper limit of integration, T. GWP, at the bottom, is computed by dividing numerator and denominator at each time point T. Note that although the methane integral stops changing after about 40 years (by which time 95% of the methane emitted at t=0 has disappeared from the atmosphere), GWP continues to change because the denominator continues to grow.

The Global Warming Potential is Inconsistent

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