According to the theory of global warming, anything that changes the radiative energy balance of the Earth will cause a change in temperature that is correlated to the change of energy. The “consensus” is that a doubling of CO2 in the atmosphere will increase the energy at the surface by 3.7 W/m2. This additional energy will increase the temperature of the Earth by 3 °C.
So in this case, the climate sensitivity is described as temperature impact as a result of the doubling of CO2 in the atmosphere. In proper scientific form the climate sensitivity is the change in temperature as a result of a change in energy.
Climate Sensitivity = delta T / Delta E (K/(W/m2))
This form is far more useful because it can be applied to situations other than changes in CO2 level. Since I am one of the few that use this form I always give the conversions to CO2 doubling. For the case of doubling causing a temperature increase of 3 °C.
CO2 doubling to cause a 3 °C increase = 0.81 (K/(Wm2)) = (3 °C / 3.7 W/m2)
With that basic information out of the way it is time to tackle the task of estimating the climate sensitivity from the two very large volcanic eruptions that have happened in the past 130 years. They are the eruption of Mt. Pinatubo and Krakatoa.
Since Mt. Pinatubo happened in 1991 there is much better resolution data available. This includes measurements of the change in surface energy from the sun and of global temperature. Then I will take the range of climate sensitivity and use that to estimate the change in solar forcing caused by Krakatoa and compare to the what is thought to have happened as a result of the eruption of Krakatoa.
I will use the normal global value of solar insolation determined in Trenberth 2008 as the normal amount of energy that reaches the surface of the Earth. This is stated as 161 W/m2. The percentage drop in solar energy will be from that. For instance a 1% decrease in surface energy will be a drop of 1.61 W/m2.
The measured difference in surface energy by the NOAA Climate Monitoring and Diagnostics Laboratory in Boulder, Colorado was a 2-4 % drop in total solar energy. This corresponds to a change of 3.2-6.4 W/m2. This is of a comparable scale to the proposed increase in energy associated with a doubling to almost a quadrupling of CO2 in the atmosphere.
The global effect on temperature depends on what method you use. The greater the temperature response, the greater the climate sensitivity would be. The methods that showed the greatest temperature change were the two satellite methods. The average drop in temperature was 0.285 C and the peak was 0.5C. I will estimate the sensitivity for both of those temperatures.
The greatest sensitivity estimate is that of a 2% reduction in energy. In that case the climate sensitivity is 0.3 °C for a doubling of CO2. That is 10x lower than the one generally stated by the IPCC. If the mid-range value for the decrease in energy is used, the increase in temperature that would result from a doubling of CO2 would be 0.22 °C. Once again the climate shows it is FAR less sensitive than what the warmists estimate it to be.
If the peak temperature drop is used, the results are as follows:
The maximum sensitivity is once again with the minimum change in energy at is ~0.6 °C/doubling. Once again that is much, much less than the IPCC estimate, even for the peak month drop in temperature.
I will not bother to use the results of the station temperature change as they are substantially lower than the results of the satellite temperature change. I will take one additional step and estimate the change in temperature using the 3 °C /doubling.
In this case the change in global temperature would have been on the order of 2.6 – 5.2 °C. This is of course very comparable to their estimate for what the temperature will be in the year 2100. That is because the forcing effect of eruption of Mt. Pinatubo is comparable to their estimate to the forcing for a doubling of CO2.
The range of climate sensitivities I will use for the Krakatoa eruption will be 0.059 – 0.155 (K/(Wm2)) and I will throw in the IPCC value of 0.81 (K/(Wm2)) for good measure. That way it will be clear just how far out of whack that high estimate of climate sensitivity is.
The commonly used drop in global temperature associated with Krakatoa is 1.2 °C. The problem is that the global temperature records do not show that in any way. The CRU, GHCN and such show no evidence of a drop like that. Mass, Portman 1989 provide an estimate of a drop of 0.5 °C. So I will use both the 0.5 °C and the 1.2 °C as the change in temperature for the eruption of Krakatoa.
For the Pinatubo climate sensitivity estimates the change in surface energy for the two changes in global temperature is 2-12.6 %. This is a very wide change in energy, but the IPCC sensitivity estimate is 0.4-0.9% change in surface energy. That is far less than what was measured for the smaller eruption of Mt. Pinatubo.
The estimates for Krakatoa are that the total solar energy decrease for the Earth’s surface was ~10%. This would tend to support that the temperature drop was closer to the -1.2 °C and the climate sensitivity is on the low side of 0.2-0.4 °C / doubling of CO2.
Once again the Earth’s response to significant events results in a lower climate sensitivity than what the IPCC uses. Note that a 10% reduction in energy to the surface would drop the total energy by 16.1 W/m2. This compares to the change in proposed change of forcing of 1.1-1.4 W/m2 for the change in CO2 from 300-315 ppm to the current 391 ppm.
Krakatoa induced at least a 14X change in energy and that at most caused a 1.2 °C reduction in temperature. This is more evidence that the IPCC estimate of climate sensitivity is grossly exaggerated.
I found another source that gave slightly different values for Mt. Pinatubo. It gave the change in energy at a magnitude of 2.7 W/m2. That is comparable to 1.7% of the normal surface energy. The same source puts the cooling at 0.5-0.7 °C. So using that fixed drop in energy and the range of temperature changes that were observed, the following climate sensitivities were determined.
Even in this case the climate sensitivity is far less than the IPCC value by at least 3x. Even with the minimum amount of measured energy change and the maximum temperature change the climate sensitivity is still more than 3 times smaller than the “consensus” sensitivity. No sensitivity determined from volcanic eruptions shows a sensitivity for doubling of CO2 to exceed even 1 °C.
It should also be noted that the NOAA estimate (2-4%) was comparable to the ERBE observed (1.7%) decrease in solar energy. Both of these vales significantly exceed the proposed forcing associated with the increased CO2 levels. Study of the forcing effects of the volcanic eruptions provide strong evidence that the IPCC climate sensitivity is grossly exaggerated.
Offline source of Krakatoa insolation reduction: Wexler, H.; ‚On the effects of volcanic dust on insulation and weather’, in: Bulletin American Meteorological Society, Vol. 32, No. 1, January 1951, pp. 10-15.
Tags: Climate Sensitivity