Yet more on Lord Lawson's speech (wonkish)

Oh dear, I can't let go of this Lawson thing. I find when I start exploring numbers like the HADCRUT3 dataset, it's difficult to stop.

In yesterday's post I confirmed what Lord Lawson said in his recent speech, that the temperature record for the past fifteen years shows no warming trend. I then suggested that this was not a very meaningful measure because movement within a period of ten or fifteen years tends to be dominated by noise in the system.

The trend I calculated was a global warming rate of 0.004 degC per year, or 0.4 degC over a century which I thought low enough to be deemed insignificant. Curiosity then led me to try the same - a calculation of the 15-year warming trend - for the periods ending in each of the previous 30 years. This is what I got:-

Past 15-year warming trends for periods ending between 1982 and 2011 Source: HADCRUT3 dataset

The 15-year warming trend to 2011 was at a record low for the 30 years shown (from data going back 45 years). The only comparable trough was in 1993-94, where the decline from a peak in 1988 was perhaps accentuated by the eruption of Mount Pinatubo in 1991. A 15-year near-flatlining of the global mean temperature shows up in the record to 2011 but for no other year since 1994. Lawson is lucky - he can claim that his 15-year flatlining is based on latest rather than cherry-picked data.

So what is happening? I don't think volcanoes are the reason for the dip this time. The eruptions of Eyjafjallajökull and Grimsvotn in Iceland were not on the scale of Pinatubo. However, I remember that some work a few years ago predicted a decade of subdued or negative global warming through the normal cyclical patterns of ocean circulation. This may have something to do with it. Here is one report of that research.

But back to Lawson. My knowledge of him and his motives is very limited. From my perspective, at least two views are possible. One view is that he has access to a circle of credible scientists who think that current government policy is based on an exaggerated estimation of the risks from global warming. Hence, according to this opinion, the sort of economic sacrifices that flow from curtailed use of fossil fuels are not justified.

Another view is that, to him, defence of the present economic order takes priority over the interests of future generations. That order is threatened by policies aimed at reducing the risks from global warming and he wants, by all means possible, to campaign against those policies. The "possible means" include the subtle dissemination of correct but misleading information to the public.

The truth may be somewhere between these views but this episode nudges me towards the second view. Lawson draws attention to the lack of a warming trend over the past fifteen years. An obvious but erroneous implication is that global warming simply isn't happening so we don't need to do anything about it. Lawson doesn't say that global warming isn't happening -- he simply disseminates a fragment of information that might easily lead an uninformed person to that view.

This may seem like a harsh judgement against Lawson but such behaviour is very much a part of our normal political discourse. I remember from twenty years ago having sometimes furious arguments with political colleagues on a question of housing finance. Labour and the Liberal Democrats at that time (rightly in my view) wanted to spend more public money on housing. However, it was generally accepted at the time that there was a need to limit what was then called the Public Sector Borrowing Requirement (PSBR). One prominantly promoted mechanism for putting more money into housing was to allow local authorities to spend more of the capital receipts from the past sale of council houses and I remember references to "money lying around in local authority bank accounts". The unspoken implication was that there was "spare" money that could be spent with impunity. However, with some experience of public and housing finance, I knew that when public money was spent, it didn't matter what was the source of the money - spending would always increase PSBR. Council house sales reduced PSBR when they occurred and spending the proceeds would raise PSBR. This was not obvious to the public, nor, indeed to most rank-and-file party activists. However, it must have been understood in the upper echelons of the parties. Leading politicians from both Labour and the Liberal Democrats encouraged and exploited public misunderstanding of public finance in order to create an impression that John Major's government was callously and needlessly leaving money unspent that could have been used to relieve homelessness.

Lawson is not being exceptionally villainous in his promotion of public misunderstanding of a complex issue -- he is merely engaging in normal British political practice. However, when promoters of a particular point of view resort to arguments that can only appeal to the uninformed, it suggests a dearth of valid reasons to support what they are promoting. Hence Lawson's campaigning strengthens my perception that global warming is indeed a very serious threat to be acted on robustly.