Tim Lambert and John Quiggin have both been banging on about global warming rather a lot lately. Tim’s Global Warming Sceptic Bingo post is an especially useful corrective source for the spurious and fraudulent material typically trotted out by global warming sceptics.
But Tim’s and John’s posts caused me to revisit the GISS global mean temperature records just out of idle curiosity. It was these records that caused me to abandon my own former position of moderate global warming scepticism about 12 months ago. The reason was that, although there was neither high solar activity nor an El Nino event to inflate the temperature record, the temperature record seemed to be continuing to show a warming trend.
My previous position, based on a fairly careful though non-expert perusal of the evidence, had been that human-induced global warming, though an undeniable reality, was likely to be quite modest and not a matter for panic or extreme measures. The GISS records in the first part of last year made it look like my conclusions had been wrong: the continued warming appeared significantly greater than you would expect if the long-term warming trend was as modest as I had thought.
But it turns out my assessment was premature. In fact the global mean temperature actually dropped by 0.02 °C in calendar year 2003, and by a further 0.04 °C in 2004. Can anyone recall reading anywhere that the world has actually cooled slightly in each of the last 2 years? I certainly can’t. I wonder why?
Now, a global cooling of 0.06 °C might not seem much, but it’s almost exactly what you’d expect if, as I had previously assumed from the evidence, the overall amount of warming caused by human emission of CO2 was real but exceedingly modest. The rate of warming since 1978 (before which the world had actually been cooling slightly for the previous 30 years or so, leading some of those now at the forefront of global warming alarmism to make equally alarmist predictions of an impending Ice Age) is about 0.15 °C per decade. The most common view is that about half of this warming is due to increased solar activity (i.e. not human activity), so that human-induced warming is around 0.075 °C per decade. The slight recorded cooling over the last 2 years, when solar activity has been reduced, tends to confirm those proportionate estimates.
So what does it all mean in practical terms? Well, global mean temperature has been increasing in linear fashion over the last 3 decades or so, as has atmospheric CO2. If we assume (not unreasonably) that that trend is likely to continue in the absence of major policy action to reduce human-generated CO2 emissions, then the extrapolated global temperature increase over the next century or so computes to a total of about 0.75 °C. Hardly insignificant, but not cataclysmic “the sky is falling” territory either.
But the UN IPCC asserts that the most likely increase is more like 2-2.5 °C, a much more worrying figure that would certainly have very serious effects on human life, civilisation and the global environment. My glance at the GISS figures early last year suggested to me that those IPCC estmates might just be correct. But the picture now looks much more benign, and approximates to my previous more moderate assumptions.
As far as I can work out from extensive though non-expert perusal of IPCC reports, they only manage to generate a projection as scarey as 2-2.5 °C (rather than 0.75 °C, which is all that can be justified on current trends) by making 2 assumptions, both of which are unjustified by the evidence:
(a) That most climate “feedback” mechanisms (e.g. the net effect of changes in cloud cover in reflecting or trapping heat) will operate to amplify rather than dampen the temperature increase generated by human-induced CO2. In fact the IPCC’s own reports clearly show that scientists simply don’t know enough at present to be able to say whether the net effect of feedbacks will be positive or negative. Moreover, the record of the last 30 years shows little or no sign of any amplifying influence.
(b) That world economic/industrial growth with be faster and dirtier than in recent decades, and/or population growth will be more rapid. In fact, the most recent world population growth projections show it slowing and then stopping by the middle of this century. Moreover, no respectable economist would hazard growth projections for any longer time frame than a decade and in a single country. Projecting growth over a whole century for the entire planet is just plain silly. Hence the IPCC talks in terms of “scenarios’ rather than concrete predictions, but that doesn’t stop it purporting to predict a temperature increase of 2-2.5 °C, when current rates of growth and temperature increase simply don’t support it.
Thus, while it’s certainly true, as Tim Lambert and John Quiggin claim, that most of the global warming sceptics’ arguments are spurious, so too are the official estimates exaggerated and speculative and unjustified by the current evidence. There is certainly a “consensus” among climate scientists as to the reality of human-induced global warming, but there is no consensus at all about its likely magnitude. We are entirely justified in treating sceptically claims of large or catastrophic human-induced climate change.
That means we should take modest, considered action to moderate CO2 emissions, but extreme, drastically growth-inhibiting measures simply aren’t justified by the current state of knowledge and evidence. It would be a good idea for the US and Australia to ratify the Kyoto Protocol, and for carbon taxes and an international and domestic emissions credits trading system to be developed. And it’s very important that the third world be required to sign up to Kyoto-style emission reduction targets. First world governments should also continue and expand funding for development of sustainable, non-carbon energy sources (e.g. hydrogen).
But that’s about as far as it goes. There’s certainly no overwhelming case for major conversion to nuclear energy, at least until generation costs come down and waste disposal and proliferation problems can be more securely managed.