Dr. Hermann Harde from Helmut-Schmidt in Hamburg, Germany recently published a paper where he modeled the total impact of CO2 doubling for the Earth using the updated databases on the absorbance of greenhouse gases and water vapor in the Earth’s atmosphere. This approach was different from previous studies ( Myhre 1998, Hansen 1998) in that it accounted for more layers in the atmosphere and also accounted for overlapping absorbance bands. It also uses three major climate zones instead of two. This may not be critical as the results for two of the zones was very comparable, but it is still useful to see the results.
The big difference that I see is the added layers in the atmosphere. Radiative heat transfer is meaningless over large distances except in a vacuum which our atmosphere is not. So a model that is approaching the effects of the atmosphere is far more useful than one that treats it as only a couple of different interacting layers. This matters because it decreases the temperature gradients between the layers and as a result decreases the amount of heat that is transferred. As I have stated many times, nature does not like temperature gradients and as a result they do not last long in nature. I expect that as studies approach a model without layers that the effects of CO2 will decrease. The basis for that view is simply the amount of long wave (LW) energy that is absorbed by the atmosphere is already small which is why forcing is used in place of net heat transfers.
The three zone approach (Tropical, Temperate and Polar) is also interesting. It allows a more flexible atmospheric profile of water vapor than what is usually used. This is critical because when water vapor is high (indicated most accurately by the dewpoint) the effects of CO2 are greatly reduced to meaningless. There is significant overlap in the CO2 absorption bands and when the humidity is high the concentration of water vapor is much, much greater than the concentration of CO2. As a result there is little energy left over for CO2 to absorb.
Finally this paper does not assume that there are enormous feedbacks in the system. The most common positive feedback used is increased CO2 causes increased water vapor which results in even greater warming. As even the impact of CO2 is not proven, the idea that water vapor feedbacks are understood and quantified crosses into the land of fantasy. So seeing that bit of lunacy left out is a refreshingly honest bit of science.
Like most studies he presents the results as climate sensitivity as is conventional, but technically inaccurate. The results are more properly labeled as the climate response to the doubling of CO2 as I have explained previously. Since most documentation is in this form I understand the reason for the presentation, but I wish that scientists would start to be precise in their usage of climate sensitivity. So when his paper uses climate sensitivity he is in fact stating his results for the entire climate response to a doubling of CO2. His results are as follows:
The results are very interesting for a variety of reasons. Unexpectedly the tropics show a stronger (very slightly) response to the CO2 doubling than the mid-latitudes. The difference is small, but not a result that I would have expected. It is possible that the mid-latitudes of the Southern Hemisphere (SH) played a large role in the smaller response. This is comparable to the annual temperature cycle where the SH warms and cools less than the NH through the varying seasons. I will try to get an answer from him once I have this up and see if it was the low land/ocean ratio in the SH that caused the mid-latitudes to have a lower response than the tropics.
Most interesting to me was the polar results. The predicted climate response to doubling of CO2 was 0.92 °C. Assuming he used the normal CO2 forcing model for this then that translates to a true climate sensitivity of 0.248 K/Wm-2. That is almost identical to the result I got for the climate sensitivity of the NH using local energy changes for the Milankovitch cycles. Since the polar regions are also the key factor for the Milankovitch cycles it is intriguing to me that this paper also concluded that the true climate sensitivity of the poles was almost identical at 0.24-0.25 K/Wm-2. That of course corresponds to a the warming of 0.89-0.92 °C for a doubling of CO2.
As for the global response of 0.45 °C for a doubling of CO2 the climate response is lower for the Earth as a whole. The global climate sensitivity for the forcing associated with a doubling of CO2 would be 0.12 K/Wm2. This is 7.4x smaller than the IPCC commonly used 0.89 K/Wm-2 which corresponds to 3 °C per doubling.
This is on the low end of my predictions when using the total Greenhouse Effect to estimate climate sensitivity. All in all I was pleased to see that another paper using atmospheric absorbance came up with very comparable results for global climate sensitivity that I have using independent methods. There is tremendous evidence that the two hemispheres have a different sensitivity and for the Earth as a whole it is at least 3 times smaller than what the IPCC claims it is.
The smaller the actual climate sensitivity is, the smaller the impact from CO2 emissions. This result predicts some warming in the polar regions, but very little impact to the Earth as a whole. One very important reason that location matters is the proposed feedback of water vapor. The polar regions are too cold for humidity and a one degree change in temperature will not change that. If the warming takes place in the polar regions, there is no water vapor feedback. This article is also a step in disproving the idea that water vapor is a positive feedback for increasing CO2 levels.