Measuring the pause in global warming

I keep writing about the pause or ‘hiatus’ in global warming because it is at the heart of the  debate about global warming, as I mentioned in passing yesterday. And I continue today because in some sense this is a historic moment. The failure of the global temperature anomaly to increase began to worry the orthodox ten years ago, and the longer it went on the more worried some of its members became.

At length, after ten years of nothing had happened, a group of the good and great led by Benjamin Santer wrote a paper explaining that ten years was just too short a period in which to distinguish the signal of human-generated temperature changes from the noise in the system: ‘interannual noise’, they explained, had too much effect on ‘decadal trends’. And they finished their abstract with this strong summary, much quoted since: ‘Our results show that temperature records of at least 17 years in length are required for identifying human effects on global-mean tropospheric temperature.’ Now Santer is a much honoured climate scientist, with strong connections with the University of East Anglia’s Climate Research Student (he got his PhD there) and the IPCC. So here were the leaders of the orthodoxy talking.

Well, 17 years has passed without there being a resumption of warming of any consequence. There has been no response from Santer et al, though others have jumped to their aid, suggesting that even after 17 years you might not see much more than a smidgin of a signal, and that it might take more years — 20, 30, who can tell — for the signs to be there strongly. The trouble with that defence is that in the meantime there hasn’t been any warming, which makes it impossible to show that it is CO2 that does all the work, and extends indefinitely the time it might take to reach the (in my view quite unsupported) claim that we must prevent temperature rises reaching 2 degrees C above the present. And it suggests that ‘climate sensitivity’, the notion that clouds and water vapour will greatly amplify the warming due to increases in CO2 alone, cannot be very high, and might even be zero.

Someone has now done the work to show all of the standard datasets, and the change in 17 years, using the useful Woodfortrees instrument, which is available to anybody who has a bright idea and wants to try it out on temperature data. Here is the first graph.

 

The background line is the regular Remote Sensing Systems (RSS) plot of the global temperature anomaly, displaying the great el Nino peak of 1998 and its smaller cousin of 2010. Just eye-balling tells you that any net increase in temperature in this time has got to come from those two el Ninos and that, after 1998 at least, there can’t have been much increase, if any. The trend lines for the datasets are the straight lines, and that for RSS is flat, two others are almost flat, and the other three display small increases only. None of them shows statistically significant warming. That of UAH, the steepest, shows a trend that produces warming of less than 1 degree C by 2100, which is hardly a worry.

The next graph looks at how long a flat trend there is for each of the datasets.  They are all of course parallel — it is their length that matters. The longest is that of RSS, which you would expect from the previous graph, and only that of UAH (the other remote-sensing dataset) is less than ten years.  If present trends continue HadCRUt3, from the University of East Anglia itself, will reach the 17-year mark shortly.

The rising line shows the rise in the amount of carbon dioxide in the atmosphere. The jagged appearance of that line comes from the fact that atmospheric carbon dioxide is greatly affected by plants, which take up as much of their food as they can get in their growing seasons — and most of the plants are in the northern hemisphere.

Altogether, these two graphs are abundant visual evidence that there is something very wrong with the view that human activity in the burning of fossil fuels, making cement and clearing forests is the predominant cause of global warming. And, I’ll say it again, if it hasn’t been able to do so in the last 17 years, there is every reason to suspect that earlier periods of warming were also affected by whatever the elements of natural variability are. In short, the fundamental building block of the AGW scare is shown to be made of cardboard, if not tissue paper.