Posted by Jeff Id on June 8, 2010
Roy Spencer has another interesting post where he uses PDO, AMO and SOI to predict the warming post 1978. He used the 3 factors and temperature to calculate a weighting factor in pre-1960 and it resulted in a prediction of warming in the post 1978 timeframe. Recently Eric Steig challenged us to be skeptical of Dr, Spencer’s last article but few of us spent any time with it, this time I think the answers are a little easier to see and are therefore less work.
Now Dr. Spencer described his methods like this.
I used the period from 1900 through 1960 for “training” to derive this statistical relationship, then applied it to the period 1961 through 2009 to see how well it predicted the yearly temperature change rates for that 50 year period. Then, to get the model-predicted temperatures, I simply added up the temperature change rates over time.
Pretty simple really. What’s amazing is that he was able to get the following plot from these methods.
Again I want to emphasize that my use of the temperature change rate, rather than temperature, as the predicted variable is based upon the expectation that these natural modes of climate variability represent forcing mechanisms — I believe through changes in cloud cover — which then cause a lagged temperature response.
I love the explanation, it could very well be correct in my opinion.
This is powerful evidence that most of the warming that the IPCC has attributed to human activities over the last 50 years could simply be due to natural, internal variability in the climate system. If true, this would also mean that (1) the climate system is much less sensitive to the CO2 content of the atmosphere than the IPCC claims, and (2) future warming from greenhouse gas emissions will be small.
There are some problems I have with the post.
1 – Why is it assumed that SOI, AMO and PDO are 100% natural forcings, unaffected by CO2 warming?
2 – What are the weightings determined in the 3 way relationship.
With respect to 1, it seems to me that global warming needs to affect the water if we want to see air temp changes. If the water isn’t warmed, then the air won’t warm, so when did we determine that AMO and PDO are 100% natural? They may be, but they also might not be right?
With respect to 2, long term Air Vent readers all know what happens when multivariate regressions are used to fit noisy data together. There is a substantial chance for crazy weighting factors which may favor AMO, PDO or SOI over all the other factors. In this case the weightings could properly match the affect of these natural factors as well but we don’t know.
I just read some of the comments over there, it’s nice that he is allowing comments lately. His comments were interesting after writing the above:
Yes, the SOI regression coefficient was negative, while the PDO and AMO coefficients were positive. This should have been obvious from the first figure in my post.
The degree to which one of the climate indicies is (or is not) correlated to another, or lagged in time versus another, is interesting, but not necessary for what I am demonstrating. All I am hypothesizing is that these indicies (the PDO, AMO, and SOI) have associated with them non-feedback changes in the radiative budget of the Northern Hemisphere….probably due to circulation-induced changes in albedo due to clouds.
If this is not the case for one or more of the climate indicies, then the multiple linear regression procedure will assign little or no weight to that index. The possibility of an accidental statistical relationship is greatly reduced by the fact that I trained with pre-1960 data, to then explain the post-1960 warming: an independent test.
When he writes — “This should have been obvious from the first figure in my post.” I happen to disagree with this statement completely. While the relationship seems to be inverted, in noisy data regression, you often don’t know what you will get. That is one of the problems with large scale multivariate methods like Michael Mann has been employing to mash proxy data together causing things like upside down thermometers. Using these methods, all you can do is minimize the inverted weightings to the best possible extent.
Anyway, while the exercise is interesting in that we can look at these factors and come up with a reasonable approximation of temperature, I wonder if the weightings are of reasonable magnitude and just how is it that we know warming PDO is natural?