and here is the total and complete kicker.
temperature precedes the first thousand years of cooling.
"Dear Jeff,
I read your article âWhat does the lag of CO2 behind temperature in ice cores tell us about global warming?â 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 cycleâ¦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 wayâ¦warming or cooling. We are talking about planet Earth after all and not Venus whose atmospheric pressure is many times larger than Earthâs.
If there is also a time lag upon the onset of cooling, then it appears that some other mechanism actually drives the temperature changes. So what is the time difference between CO2 levels during the onset of a cooling period at the end of a warming period and the time history of the temperature changes in the ice cores?
Dear John,
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 Earthâs 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 [this really should say "theory" -- eric], 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 â 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.
Think of heart disease â one might be tempted to argue that a given heart patientâs condition was caused solely by the fact that he ate french fries for lunch every day for 30 years. But in fact his 10-year period of no exercise because of a desk job, in the middle of this interval, may have been a decisive influence. Just because a sedentary lifestyle did not cause the beginning of the plaque buildup, nor the end of the buildup, would you rule out a contributing causal role for sedentary lifestyle?
There is a rich literature on this topic. If you are truly interested, I urge you to read up.
The contribution of CO2 to the glacial-interglacial coolings and warmings amounts to about one-third of the full amplitude, about one-half if you include methane and nitrous oxide."
http://www.realclimate.org/index.php/archives/2007/04/the-lag-between-temp-and-co2/