As a geologist I have been applying the study of past climate change to my professional research for over 45 years. I have been closely following the to-ing and fro-ing on recent climate change for over 35 years since the mid-1970s "cooling crisis". As a professional I scan the major international scientific journals, spending up to 5 hours per week doing this. I have read the scientific sections of all the IPCC reports, have gone on to read critical references quoted within those reports and have also noted how the story has changed from one report to the next.
Agmates site and in the course of this lengthy exchange I summarised what I see as the critical contradiction in the AGW thesis relating to CO2 and CH4. I will repeat that as I see it as being the crux of the whole AGW debate, which nobody has satisfactorily answered, in the IPCC reports or anywhere else. The onus is on them to prove their theory, not on me to disprove it. After all it is the IPCC's theory and political pressure that wants to turn the world economy upside down.
Do CO2 and CH4 control temperature variability? No earth scientist I deal with argues against the contribution of greenhouse gases, including CO2 and CH4, towards moderating Earth’s climate, but when CO2 exceeds 60 parts per million its “greenhouse effect” plateaus. Looking back through history climate change has natural regular cycles of 100,000 years duration, which have stayed within very precise high and low boundary temperatures. Such a regular cycle (similar to a printout of human heartbeats from an ECG) must be due to a combination of Earth's regular orbital variations and solar intensity variations. After all there is no known mechanism for Earth to inhale and exhale CO2 and CH4 in such a regular pattern.
We are currently in an Interglacial period, known as the Holocene Maximum, since about 8000 years ago and this is no different to the Interglacial peaks of at least the last 5 cycles. The peak of the current Interglacial period was 8000 to 6000 years ago, when temperature was at around 2 degrees higher than now and global sea level averaged close to 2 metres higher than the present. This is published research that the IPCC has swept under the carpet. Sea-level has decreased since then at an average 0.3mm per annum, but it goes up and down like a roller coaster. The temperature has declined in a similar roller coaster manner as well and the Minoan, Roman and Medieval warm periods were the peaks that were warmer than today.
The IPCC, up until the 4th report used ice-core data from Greenland and Antarctica to graphically demonstrate a clear link between CO2 and CH4 variability and temperature variability. However when detailed work was done in recent years on these ice-cores it was shown that the CO2 and CH4 rises and falls actually followed the temperature rises and falls by on average 800 years. The IPCC 4th report in 2007 (Chapter 6, p444) rationalised this contradictory evidence by saying that the temperature rise was initiated by other factors (probably Earth orbital) but that CO2 and CH4 then took over as the main forcing agents, which amplified the temperature rise.
However, what happens at the top end of the cycle was never explained. Why is it that temperature reached essentially the same high points (within a 2 degree range) in each of the last 5 Interglacial periods including the current one, then started to decline while the CO2 and CH4 were still rising? The obvious answer, which the IPCC has swept under the carpet, is that temperature variability is controlled by some other forcing agent and CO2 and CH4 just follow along.
I decided to wade through the RealClimate website run by the principal IPCC scientists Professor Jeff Severinghaus of the Scripps Institute of Oceanography, University of California, San Diego is considered an expert on such issues and is quoted in the IPCC reports. Guess what? Severinghaus and his mates do not, and obviously cannot, answer the question posed, even though they were specifically asked that same question a number of times in a discussion forum on the site. The question about CO2 and CH4 control on climate variability is THE major scientific issue.
If that hypothesis falls over then the whole story does.
I attach the leading example of the discussion for all to see:
I read your article “What does the lag of CO2 behind temperature in ice cores tell us about global warming?” You mention that CO2 does not initiate warmings, but may amplify warmings that are already underway. The obvious question comes up as to whether or not CO2 levels also lag periods when cooling begins after a warming cycle…even one of 5,000 years? If CO2 levels on planet Earth also lag the cooling periods, then how can it be that CO2 levels are causally related to terrestrial heating periods at all? I am not sure what the ice core records are related the time response of CO2 to the cooling trends. If there is also a lag in CO2 levels behind a cooling period, then it appears that CO2 levels not only do not initiate warming periods but are also unrelated to the onset of cooling periods. It would appear that the actual CO2 levels are rather impotent as an amplifier either way…warming or cooling.
The coolings appear to be caused primarily and initially by increase in the Earth-Sun distance during northern hemisphere summer, due to changes in the Earth’s orbit. As the orbit is not round, but elliptical, sunshine is weaker during some parts of the year than others. This is the so-called Milankovitch hypothesis, which you may have heard about. Just as in the warmings, CO2 lags the coolings by a thousand years or so, in some cases as much as three thousand years.
But do not make the mistake of assuming that these warmings and coolings must have a single cause. It is well known that multiple factors are involved, including the change in planetary albedo, change in nitrous oxide concentration, change in methane concentration, and change in CO2 concentration. I know it is intellectually satisfying to identify a single cause for some observed phenomenon, but that unfortunately is not the way Nature works much of the time. Nor is there any requirement that a single cause operate throughout the entire 5000 – year long warming trends, and the 70,000 year cooling trends. Thus it is not logical to argue that, because CO2 does not cause the first thousand years or so of warming, nor the first thousand years of cooling, it cannot have caused part of the many thousands of years of warming in between.
Jeff Severinghaus' first paragraph confirms what I have stated. The next paragraph, far from being “logical” is just straight down the wicket "woffling". He makes no attempt to explain why all the other supposedly weaker agents and feedbacks stop the temperature rise, while the supposedly strongly positive amplifying feedbacks of CO2 and CH4 are still rising. As I see it, when the evidence that CO2 change actually follows the temperature change was staring them in the face, the IPCC scientists were “in too deep”, with billions of dollars per annum of research funding going their way. They have tried every trick in the book to bluff their way through, including calling anybody who questioned their story a “denier”.
The chickens have come home to roost. Clearly CO2 and CH4 do not control temperature variability. End of story!