By Ed Caryl
The Climate Team has always claimed that a doubling of CO2 would add 3.7 Watts/m2 to the global climate budget and thus this would fry us all. This fate is their religion’s version of Hell, except we will all suffer this rather than just the “sinners,” thus giving them leverage to force us to do their will. Many bloggers, and some others, notably even BEST, have pointed out that there are many locations that are cooling rather than warming. The warmists would have us believe that these cooling stations are just due to local phenomenon, such as albedo change, land use, site moves, or other changes, and that the warming stations are not due to UHI.
Last year, Willis Eschenbach took a look at Modtran. Modtran is a program that was initially developed by the US Air Force in the late 1980’s that does a line-by-line analysis of the IR spectrum transmitted by the atmosphere. An on-line version is available at the University of Chicago, here. Willis noted that none of the latitude selections would give a CO2 doubling figure higher than 3.2 Watts/m2. He didn’t notice that the default settings in the program include a setting for water vapor at a pressure setting of 1. Any water vapor in the spectrum will lower the CO2 doubling figure.
Here is the result of calculating the outbound long-wave radiation (OLR) or as it is labeled in Modtran, I out. The settings used were: CH4 – 1.8 pmm, Tropical Ozone 800 ppb, Strat. Ozone 1, Ground T offset – 15°C, hold water vapor – Relative Humidity, Water Vapor Scale – at 0, 10, 50, and 90 percent, Locality – 1976 U. S. Standard Atmosphere, No Clouds or Rain, Sensor altitude 100 km, Looking Down. These values were the best available to represent a global average. This produced the following table and chart for various CO2 and water vapor values.
Table 1 is TOA OLR for CO2 values from 0 to 1000 ppm and RH at 0, 10, 50, and 90%.
Figure 1 is a chart of Modtran output for 0, 10, 50, and 90% humidity, and CO2 from 0 to 1000 ppm. The radiation (vertical) scale has been inverted so that increasing greenhouse warming is upward. Note that both CO2 and water vapor forcing are logarithmic; increasing amounts have decreasing effect.
With humidity set to zero, the doubling of CO2 figure actually goes to 4.7 W/m2. Any reasonable humidity value drops that number drastically. At 50% humidity, and our current CO2 value, we get a tiny 0.188 W/m2, far, far below the IPCC favored value. Of course humidity doesn’t stay constant. In the tropics, 90% is more typical. In that case, doubling CO2 gets us 0.125 W/m2. This is all before the additional factors of clouds and rain, which will drop the value even further, into the negative territory that Willis noticed here. The blue triangle in the chart and the blue value in the table are the current values with today’s CO2 and global average humidity.
Given the data, Modtran can compute the real outbound radiation over time. The humidity at 600 mbars and the Mauna Loa CO2 values were applied through Modtran to result in Figure 2. This is a “zoom in” on the blue triangle in figure 1, adding the time dimension. The 600 mbar level for humidity seemed a good compromise, as only one humidity figure could be entered.
Figure 2 is a chart of the outbound radiation increase since 1948. There has been a more than 1 Watt/m2 increase in outbound radiation in that interval, despite rising CO2.
Humidity has been decreasing in the upper atmosphere over the last 60 years. That offsets the rising CO2. We saw the cooling in the 70’s but increased solar radiation along with ocean cycles held off the cooling over the last 20 years. That period has now come to an end.
Mother Earth has an excellent thermostat system. Even if somehow average humidity should increase to 50% and CO2 goes to 1000 ppm, only about 2 Watts/m2 will be added. This is unlikely in the extreme, and would add a small fraction of a degree to warming. No one would notice.
My question is: Why have the professional “climatologists” not done the simple work that I did on a lazy Saturday afternoon with my laptop? They must know that water vapor nearly wipes out CO2 in warming the Earth, and that clouds and albedo do the rest. What’s their excuse for this massive “oversight”?