Has Global Warming Stopped?

This post continues a theme from yesterday’s, which was on the dramatic drop in the European price for a tonne of carbon dioxide emissions — because one reason for the growing scepticism within the European Parliament, which reflects the growing scepticism in the electorate, is the failure of global temperatures to rise in accordance with the growing rise of carbon dioxide accumulations in the atmosphere, which is, from the orthodox point of view, the signal that the world is going to get warmer, unpleasantly, perhaps catastrophically.

Whether or not warming has stopped is now fiercely contested around the blogosphere, and I thought it might be useful to have a look at that. There are some semantic issues that need to be dealt with first. Compared to forty years ago the world seems to be warmer, and I don’t think there are many who would suggest otherwise. I should say at once that most of our knowledge comes from thermometers of varying accuracies and different locations, plus proxy measurements from radiosonde balloons and satellites, and it is unwise to take much notice of decimal places in these measurements. But I think most of those who take a serious interest in climate, whether from the orthodox or the dissenting side, would accept that in the last forty years the planet seems to have become a little warmer.

The great spike was in 1998, when a major el Nino event occurred, which added perhaps 0.3 of a degree C to the average global temperature. (I should also say that I am not one who takes a great deal of interest in ‘average global temperature’, because I think it is a statistical artefact that means very little in practice to anybody. But for the purposes of this post I am going to use it, for good reason.) It is what has happened since 1998 about which there is a contest — and indeed what all that means to us.

Temperatures are measured all over the place, and some temperature series go back a long way — the Central England Temperature series, for example, goes back to the mid 17th century. And people collect temperature data in order to try to find patterns. Those  who manage these collections use similar data, often the same data, and they adjust the data for various reasons — to deal with data absences, for example, or changes in location of the thermometer, or apparently screwy readings. And temperature is measured at the surface of the land (actually, about a metre and half from the surface), at the top of the atmosphere, in the troposphere (higher still) and in the stratosphere (even higher), on the surface of the sea (well, more or less) and at varying depths.

Those who like working with numbers — and temperature is a wonderful field for them — then like to combine the numbers, play with them, apply all sorts of clever maths to them, and come out with ‘indexes’ which purport to tell us what is happening globally. The rest of us rely on half a dozen of these indexes, some produced by the Hadley Climate Research Unit at the University of East Anglia (HadCRUT, several types), one by the Goddard Institute of Space Science (GISS) in the USA, one by Dr Roy Spencer of the University of Alabama at Huntsville (UAH) and one by Remote Sensing Systems (RSS). There is a decent amount of agreement between these various techniques, which is somewhat reassuring.

A retired Canadian physics teacher called Werner Brozek looked at all the major global temperature indexes over the last 20 years, and has showed that all of them reveal a flat trend for quite long periods. Going backwards from the present, the slope of the GISS index has been flat since January 2001. For HadCRUT3, the slope has been flat since April 1997. For a combination of GISS, HadCRUT3, UAH and RSS, the slope has been flat since December 2000. For HadCRUT4, the slope has been flat since November 2000, while for HadSST2, the slope has been flat from March 1, 1997. In summary, there seems to have been been a pause in global warming, of between 12 and 16 years. And while warming has paused, the accumulation of carbon dioxide in the atmosphere has gone on steadily increasing, at the same rate as before the pause. (Incidentally, for those wondering why a retired physics teacher would know anything, you can do the work yourself: all the data are publicly available, as you’ll see from his article. If you disagree with his findings, have a go yourself.)

The apparent pause is not what was predicted. The last IPCC report forecast a temperature rise for the century of about 0.2 degrees C per decade, but nothing like this has happened. Warming may start again tomorrow, though it will be a year or two before we will know. But the pause suggests that the experts know less about climate than we were told. If the pause were to continue for another — how many? — years it would be plain that the role of carbon dioxide in global warming had been greatly exaggerated. Indeed, the rise in carbon dioxide accumulations is extraordinarily steady, but the rise in temperature over the past century has gone through warming and static phases. Something else is clearly at work, if we can assume that all these indexes actually mean something.

There is an increasing dissenting chorus telling us that ‘it is the sun, stupid’, and that we are in for a long cooling period. I don’t look forward to that, and hope they’re wrong. Plants and animals generally love warmth and dislike cold, and I’m with them.