the Air Vent
Friday, Nov 13th, 2009
The recent cooling shown in most global temperature datasets except GISS has been a spot of contention for the AGW believers. Global cooling has been an embarassing topic for those who have made careers of predicting worse than we thought warming every few weeks. This is especially contentious point for scientists who’s careers depend on warming.
A comment sent to me by email pointed to this post by Dr. Eric Steig on another blog.
It is well known this “warming has stopped” idea is a complete red herring, as we have patiently explained here:
Your article merely promotes further confusion and misinformation by adding the mark of credibility that “BBC meterologist” provides. The preceding comment by “timjenvey” is a typical example characteristic of the misuse of the data that is the result. (Why does he choose October only, for example?)
Now Dr. Steig is mostly correct in my opinion, and I don’t disagree with him on this. However, the argument should have been warming did pause – a little, it simply doesn’t prove anything about CO2 driving climate. But the pause has caused some red faces WRT computer models – see Lucia(the Blackboard) and Chad (treesfortheforest). I am a believer in some level of global warming but the arguments used in the links above cut both ways.
Here is a quote from Real Climate:
The mean of all the 8 year trends is close to the long term trend (0.19ºC/decade), but the standard deviation is almost as large (0.17ºC/decade), implying that a trend would have to be either >0.5ºC/decade or much more negative (< -0.2ºC/decade) for it to obviously fall outside the distribution. Thus comparing short trends has very little power to distinguish between alternate expectations.
So, it should be clear that short term comparisons are misguided, but the reasons why, and what should be done instead, are worth exploring.
The point Real Climate makes is that the trends are inside the statistical significance limits of the trend so the argument that global warming has stopped is false. Tamino actually took it even further with this post about Bjorn Lomborg where Bjorn made the true statement below.
Temperatures in this decade have not been worse than expected; in fact, they have not even been increasing. They have actually decreased by between 0.01 and 0.1C per decade.
Tamino makes the same claim as RC but somehow misses the point that temps actually are NOT increasing while using some math to show that the lack of increase doesn’t disprove the long term trend. His point reads that statistical short term noise has an effect on the trend signal so the trend isn’t real. Actually he’s wrong and what it means is that of course the trend is real but that the short term trend means an increased probability of pausing of long term trends but doesn’t prove them false. As above, the great thing about this approach Real Climate and Tamino have taken is that it cuts both ways. If the negative trend isn’t significant and doesn’t count, that also applies to the positive trend. — so let’s have a little fun with the team.
The plot works like this – The thick black line is the trend from x year to present in degrees C per decade. The Red line is the lower confidence limit and the blue is the upper – calculated with corrections for AR1 autocorrelation Quenouille style as used in Santer et al. If the black line stays between the confidence limits, it represents a statistically insignificant trend. The code for the calculation is shown here:
### Get trend
fm=lm(window(dat, st, en)~I(time(window(dat, st, en))))
### Initialize variables
N=length(window(dat, st, en))
### Calculate sum of squared errors
### Calculate OLS standard errors
### Calculate two-tailed 95% CI
### Get lag-1 ACF
resids=residuals(lm(window(dat, st, en)~seq(1:N)))
r1=acf(resids, lag.max=1, plot=FALSE)$acf[]
### Calculate CIs with Quenouille (Santer) adjustment for autocorrelation
So in Figure 1 black line crosses below the upper significance level (blue line) in 1995 and even touches the lower limit (red line) in 2001. So using our climate scientists arguments applied to HadCRUT show there has been no significant warming in the past 15 years (since 1995). It just clears the line in 1994 so 16 years is barely significant.
Below is UAH:
No significant warming since 1993 – 17 YEARS!
Only 11 years. In my opinion GISS has become an embarassment with it’s corrections but people don’t know it yet. I hope to live long enough to see the mess corrected (go surfacestations) but recently a prominent GISS scientist publicly promised future warming would continue and would cancel this inconvenient downward trend. The GISS trend is completely out of whack in recent years, so it looks like GISS is coming through on their promise.
What we do know from this is that despite massive increases in industry and constant worse than we thought bombardment from the press despite the need to spend trillions on socializing industry, three of four measurements show no significant global warming for the last 15 years and came very close to clearing the 17 year mark.
The title could have been: Real Climate and Tamino Claim No Global Warming for Past Fifteen Years!!
I wonder if Real Climate and Tamino will want to change their opinions?
This article was posted: Friday, November 13, 2009 at 5:10 am