Prominent astrophysicist and geoscientist Dr. Willie Soon, researcher at the Harvard-Smithsonian Center for Astrophysics:
Soon cited Dr. Alex Wiedenhoeft, of the USDA Forest Service, in response to Mann's claim about increased carbon dioxide (CO2) levels.
"In the geologic past, atmospheric CO2 concentrations can be at least 2 to 5 times larger than 400 ppm. Therefore, crossing such a CO2 level in 2013/2014 is not unprecedented," Soon said. "Furthermore, it needs to be commented that the so-called atmospheric CO2 content measurements obtained from an air bubble trapped in ice cores in Antarctica were all largely smoothed values from the inability for the record to tell us any changes from one decade to another nor even one century to another. This is why making the claim that atmospheric CO2 has never been higher than 400 ppm in the past 1000 years is not secure nor fully correct."
"If Professor Mann was referring to the past works by Fourier, Tyndall, and Arrhenius, let just be clear that those scientists would probably agree that the major greenhouse gas is water vapor not carbon dioxide," Soon told the MacIver Institute.
Soon on climate models:
“The one problem with a computer climate model is that even if we seemed to have gotten some agreements from the model with observations, we can be 100 percent sure that we have gotten the right result for the wrong reason,” Soon said. “The explanation is very simple: a computer climate model is a totally inadequate attempt to represent the real world weather and climate system that are beyond our current ability to model.”
Soon told the MacIver Institute that one example was a computer modeling of temperatures in China during the so-called mid-Holocene climate optimum period of about 6,000 years ago. The models predicted that winter temperatures were cooler at that time, but in reality, temperatures were four to eight degrees Celsius warmer than they are today.