Supplementary Material for the Danger of Overvaluing Methane S Influence on Future Climate

Supplementary material for “The danger of overvaluing methane’s influence on future climate change”

1. Gas emission profiles for Figure 1are provided below. These are the emissions profile for the various scenarios (1) a reference 650 ppm stabilization scenario (2) a 5000 Tg pulse of CH4 or (3) a carbon trading scheme where the CH4 pulse is traded for additional CO2using mass multipliers of either 12, 25, 70 or 105. Figure S1 shows the CO2 emissions for each scenario while Figure S2 shows the CH4 emissions. While the pulses used here are very large, in order to enhance the visual comparison, the same relative results hold true for small pulses.

2. Emissions trajectories of CO2 and CH4 used for Figure 2 of the manuscript.

3. Here we show the CO2 emissions from different stabilization scenarios used in this analysis (450WRE, 550WRE, 750WRE) to illustrate that the 750 ppm stabilization pathway is essentially equal to the 450 stabilization pathway delayed by 50 years during which CO2 emissions continue to rise. The curves are upward transpositions of each other with the 550 representing anapproximate 25-yr delay and the 750 a 50-yr delay in CO2 mitigation. After the peaks, the decline trajectories are essentially identical. However, in each of these cases, assumptions are made about the upward trajectory in order to achieve the stabilization goal meaning that this represents a “best-case” delay scenario. The next analysis (#5) shows the results of delays of 15, 30 and 50 years where CO2 emissions are allowed to increase on a business-as-usual trajectory, resulting in higher total CO2 emissions.

4. Figure S6 and S7 show CO2emissions trajectories and the resulting temperature trajectories, respectively, in the case of delayed CO2 emissions reductions. Here we show results from a 15-, 30-, and 50-yr delay in reducing growth of CO2 emissions, the growth rate here is based from the A1 business-as-usual scenario.

5. Emissions and temperature trajectories for a scenario in which the CH4 reductions are replaced by “extra” CO2 emissions. These “extra” emissions are equal to the CH4 reductions multiplied either by 7, 12, or 25. This scenario is an alternative representation of the potential outcome of emissions trading of CO2 and CH4 that could allow countries to make (potentially easier) cuts in CH4 emissions in order to obtain carbon credits that allow for more CO2 emissions.

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