CO2 is one of three major so-called greenhouse gases (GHG); the others are water vapor (H2O) and methane (CH4). The problem initially faced by extremists bent on tainting CO2 is that the gas is less than 4% of all greenhouse gases in the atmosphere. Water vapor is typically 95% of the total. Their solution was to argue that CO2 is a far more effective GHG.
Trouble is, we don’t know how much more effective, so activists created a phony term — “climate sensitivity” — and spoke about it as if it were high at today’s CO2 levels, now approaching 0.04% of the atmosphere.
In reality, the impact of increasing CO2 is analogous to putting coats of black paint on a window. The first coat of paint blocks most of the light from passing through the window. A second coat reduces light only fractionally more, and further coats accomplish even less.
From the University of Chicago MODTRAN facility. The degree to which increasing CO2 levels affect temperature drops rapidly as CO2 concentration rises. In other words, climate sensitivity decreases with increasing concentration, until, at today’s level of nearly 400 parts per million, climate sensitivity approaches zero. Note that the first 20 ppm of CO2 has a greater temperature effect than the next 400 ppm combined.
The same is true of the impact of CO2 on the atmosphere. Research shows that the temperature’s sensitivity to increasing CO2 is now close to zero. In other words, from a temperature perspective the atmosphere is nearly saturated with CO2.
Instead of withdrawing the AGW hypothesis — since the assumptions on which it is based have failed — the IPCC cites a positive feedback to enhance the CO2 effect. As temperatures rise, even marginally, they say, more water evaporates, which acts to raise temperatures further, causing more water to evaporate and so on, bringing catastrophe upon us. But underplayed by alarmists is the cooling influence of increasing cloud cover that would occur as the atmosphere’s water vapor content rises.
Recent evidence suggests that cloud-induced cooling more than offsets water vapor-induced warming.
The AGW hypothesis is not supported by empirical evidence, either. Measurements taken from Antarctic ice cores show CO2 rise tends to occur centuries after temperature rise, not before it, so it could not possibly have caused the onset of warming.
The hypothesis also fails between 1940 and 1980, when human-produced CO2 rose quickly after World War II yet global temperatures declined; fears of a coming glacial period dominated. Catastrophists blame the increase in sulphates from industry for reducing sunlight, therefore causing cooling. But they ignore the fact that temperatures rose after 1980 with no decrease in sulphate levels.
Today, during a period of rapid CO2 rise from the industrialization of India and China, we have had 16 years with no overall planetary warming.