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

2020
Views:

435

Pages:

12
Author:

Marely Dougherty

TEMPERATURE MODELING: A BETTER WAY TO UNDERSTAND THE EFFECT OF GHG EMISSIONS SUMMARY: No single-number metric adequately represents the effects of greenhouse gases having widely differing radiative efficiencies atmospheric lifetimes, and emission histories. Direct calculation of global average surface temperatures is a much better way of dscriminating between policy alternatives. ------------------- These are equations for incremental changes of global mean surface temperature due to a unit mass increase of atmospheric carbon dioxide (Eqn 1) and methane (Eqn 2), as published in the Fifth Assessment Report of the IPCC. Also shown is a generalization of Eqn 2, taking into account time-varying emissions of methane (Eqn 3). There is an analogous equation accounting for time-varying emissions of carbon dioxide. These equations are simple enough to be coded on spreadsheets. They lack the sophistication of general circulation models and their reduced complexity offspring, but include enough physics to provide semi-quantitative estimates of the consequences of policy alternatives. The IPCC equations show that single-year emissions of carbon dioxide (black) and methane (red) at their current global rates have comparable effects on global mean surface temperature for the ten years following emission. This despite the fact that 100 times more carbon dioxide is emitted per year. The multiyear extensions of the IPCC equations [Kleinberg, 2020] show that carbon dioxide (black) and methane (red) have comparable effects on global mean surface temperature as long as they are both emitted at current rates. APPLICATIONS: CLIMATE EFFECTS OF POWER GENERATION OF GAS VS COAL; GAS TRANSPORT BY PIPELINE VS LNG SUMMARY: Examples show how GWP methods can be misleading. (1) GWP is a poor method for computing greenhouse gas offsets. (2) CO2-equivalent methodology provides poor support for selecting real world climate mitigation options. -----------------(1) GWP is a poor method for computing greenhouse gas offsets.* * E.D. Sherwin suggested this example. The CO2-equivalent method implies temperature changes very much at variance with actual temperature calculations. The increase in global mean surface temperature for a single-year emission of 335 Mt methane at t = 0 is shown in red. The CO2-eq method suggests very different temperature trajectories for the 20-year GWP multiplier (black) and the 100-year GWP multiplier (blue). As a practical example, consider a refinery seeking an offset for the carbon dioxide it emits as an inescapable by-product of petroleum processing. It proposes to reduce its methane emissions by use of engineering controls. There is no GWP mutiplier it can apply to its methane reduction that will compensate for its carbon dioxide emissions. (2) CO2-equivalent methodology provides poor support for selecting real world climate mitigation options. ------------------ The National Energy Technology Laboratory (NETL) released a lifecycle emission study of power generation in Europe for three cases: domestic coal burned in coal-fired power plants, Russian pipeline gas burned in gas-fired power plants, and US liquefied natural gas burned in those plants. I take their input assumptions at face value without necessarily endorsing them. Two cases from the NETL study are shown here. At the upper left is an analysis of the GHG impact of US LNG fueling a gas-fired power plant. At the lower right is an analysis of the Russian pipeline case. Carbon dioxide emissions (brick color) and methane emissions (yellow/green color) are put on the same scale (CO2-eq/MWh) using GWP=36 for methane. Incremental temperature trajectories resulting from sinlge year GHG emissions are shown here. The methane contribution with the 20-year GWP multiplier of 87 is shown in the upper left. The methane contribution with the NETL 100-year GWP multiplier of 36 is shown in the lower right.The results are strikingly different. The GWP100 calculations suggest there is little difference between pipeline and LNG supply. The GWP20 calculation suggests a much larger, persistent difference between pipeline and LNG supply with the pipeline having consistently higher impact. The actual temperature calculations for the three cases are supplemented by a calculation for the lowest emitting coal-fired power plant ("Best Coal"). The results show that larger methane emissions associated with the pipeline have a significant impact in early years, but eventually become less significant than the higher carbon dioxide emissions associated with LNG. Considering the long service lifetimes of the infrastructure, the methane effect will continue to be important for many decades.

Problems of the Global Warming Potential

Related Documents

Recommended Documents

Description

Related Documents

Free up your schedule!

Take 5 seconds to unlock