Wednesday, 14 March 2018


The following is from SEPP:

Source of Heat – Atmospheric Methane?

In her blog, Climate Etc. Judith Curry takes up the issue of Question 8, in the District Judge’s proposed tutorial: “What are the main sources of heat that account for the incremental rise in temperature on Earth?” (See yesterday's post on the Californian court case)

Curry’s post was prompted by a response made to the questions by Andrew Dessler, of Texas A & M university.  In his response, Dessler posted a graph that was blurry, thus the source could not be clearly identified. However, it is similar to Figure SPM.5 found on page 14 of the Summary for Policymakers chapter, of the Fifth Assessment Report (AR5, 3013) of the IPCC. The figure is titled “Radiative forcing by emissions and drivers.”

Atmospheric greenhouse gases are not sources of heat. They absorb some of the infrared energy emitted by the earth to space, thereby slowing the nighttime cooling of regions of the globe. However, one can understand the confusion of the judge. 

In its graph, the IPCC ranks the main drivers of radiative forcing as CO2, CH4 (methane), Halocarbons and N2O (nitrous oxide), all identified as anthropogenic, human caused. It rates the level of confidence: Very High for CO2 and N2O, and High for CH4 and Halocarbons. The positive driver influence of each of these compounds is greater than the calculated negative driver from changes in land use, and far greater than the calculated positive changes in solar irradiance. 

According to the graph, all the main drivers are well mixed in the atmosphere. This “well mixed” assumption is a major issue.

Further, the graph breaks down the influence of CH4 into four resulting atmospheric drivers, CO2, H2O, O3, and CH4. After being broken down into the four components, the graph shows the remaining CH4 has a strong positive influence. The text states: 

“Emissions of CH4 alone have caused an RF of 0.97 [0.74 to 1.20] W m−2 (see Figure SPM.5). This is much larger than the concentration-based estimate of 0.48 [0.38 to 0.58] W m−2 (unchanged from AR4). This difference in estimates is caused by concentration changes in ozone and stratospheric water vapour due to CH4 emissions and other emissions indirectly affecting CH4. {8.3, 8.5}”

Herein is a major issue. At ground level what starts as CH4 changes, in part, to CO2 and H2O and O3 as it goes higher in the atmosphere. An important point, often overlooked, is that the amount of CH4 at any height in the atmosphere never gets above the amount of H2O. 

Early in his professional career, SEPP Chairman Tom Sheahen was with a team measuring the absorbing ability of various greenhouse gases at the US Bureau of Standards (now the National Institute of Standards and Technology (NIST)). They confirmed what had been known for almost a century and in handbooks since the 1920s:

• Greenhouse gases absorb infrared energy given off by the earth in specific wavelengths.  

• The most abundant greenhouse gas, water vapor, absorbs virtually all the energy that methane is capable of absorbing. 

• And, because of the shape of the spectrum of thermal radiation that the earth emits, it is further known that adding methane to the atmosphere does not increase energy absorption of the atmosphere, because there is hardly any energy of the appropriate wave length which methane can absorb. 

• Finally, it is also known that these results were repeated in multiple laboratories in multiple countries.

As Sheahen writes: “Water gradually "freezes out" towards the top of the troposphere, but above that altitude in the stratosphere, the oxidation of CH4 assures that there will be more H2O than CH4 at every altitude.  CH4 starts off around 1.8 ppm and never increases. H2O starts out at ground level about 20,000 ppm and declines to about 4 ppm in the stratosphere.  Meanwhile, CO2 is about 400 ppm at every altitude, unchanged by anything water is doing (such as forming clouds).”

Of the greenhouse gases, water vapor has the broadest capability of absorbing energy across the infrared spectrum. For some wavelengths, it absorbs all the energy. However, CH4, remains below a level where it is a significant participant in the greenhouse effect. 

Further, the 1979 Charney Report published by the National Academy of Science speculated that the modest increase in greenhouse effect from CO2 would be amplified by an increase in atmospheric water vapor, strongly increasing the greenhouse effect. The report had no hard evidence supporting this speculation. The estimates in the Charney Report have been retained by the IPCC, but there is no discussion of an increase in greenhouse effect from water vapor in AR-5. The discussion in AR-5 of methane produces no “source of heat.”

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