The 140 character restriction on Twitter is inimical to serious intellectual debate, but too many people – and especially climate alarmists – seem to regard it as a licence for restricting themselves to abuse and sarcasm, while avoiding substantive issues.

Someone called Michael Merrifield, sailing under the pseudonym @ProfMike_M, seems rather good at it.  He derides any hint of climate scepticism but has little to say about the actual issues.  He accuses me of failing to understand physics and of an inability to think. This was one of his milder offerings: “Come on Roger, you can do it: show you know at least a little physics and can think at least marginally.”  In fact I got an excellent result at Physics ‘A’ Level, and subsequently a Cambridge Maths degree.

Of course it’s tough to respond in 140 characters, so I resort to the blog, with some thoughts for Professor Mike.

First of all, is he aware that satellite data show no warming trend in the last eighteen years?  That may not prove anything by itself – but it critically undermines the credibility of all those climate models on which alarmists rely, since they all predicted rising temperatures.  Is he aware that virtually all the climate models on which alarmism depends predict a “tropical hot spot” in the atmosphere between five and ten km high – but that observations show that no such hot spot exists?  And does he understand that science fundamentally depends on the ability to falsify predictions?

Is he aware of the cyclical pattern of climate over at least the last 10,000 years (and very probably longer) with an approximately 1000 year periodicity, which gave us (inter alia) the Minoan Optimum, the Roman Optimum, the Mediæval Warm Period – and now, apparently, a new 21st-century optimum?

Has he paused to wonder why these warm periods are called “optima”?  Perhaps because human societies generally prosper in warmer periods, and do better than they do in cooler periods?  Does he realise that the slight warming in the last century (around 0.7oC) is entirely consistent with that cyclical pattern?  And that therefore it requires no special or anthropogenic explanation?

Does he know that anthropogenic CO2 contributes only about 3% to the global carbon cycle?  Is he aware that there is very much more CO2 in the oceans than in the atmosphere – but that the oceans’ ability to retain dissolved CO2 depends critically on water temperature?  So the increase in atmospheric CO2 over the last century may well be caused by cyclical temperature-driven out-gassing from the oceans as much (or more) than by human activity?  Does he know that over geo-historical time, atmospheric CO2 levels have been up to ten times – or more – higher than today – and that those periods of very high atmospheric CO2 were not associated with warming – indeed on some occasions coincided with ice ages? That no “tipping point” was ever reached, and that no “runaway global warming” ever took place?

Indeed is he aware that even at 400 ppm (the current level, more or less), the atmosphere is impoverished in CO2 compared to the geo-historical perspective? And that levels much lower would compromise plant growth, bio-mass formation and crop yields?

Does he know that the admitted greenhouse effect of atmospheric CO2 is governed by a negative logarithmic equation – or in simple terms, a law of diminishing returns? That the relationship is not linear?  That the effect of a given ppm increase in CO2 gets less and less as the absolute level increases?  And that we are so far up the curve that it takes a very great deal of CO2 to have much effect?

Does he follow the debate on the climate sensitivity to CO2?  Is he aware that the IPCC assumes a sensitivity figure of 3oC plus per doubling of CO2, while many prominent scientists argue for a much lower figure?  And that recent climate trends tend to lend support to a lower figure?

Does he follow the debate about positive and negative feedbacks?  And the question whether the aggregate of all feedback mechanisms is positive or negative?  Does he know that the climate system is complex and chaotic (in the mathematical rather than the vernacular sense), and that any attempt to define a simplistic linear relationship between mean temperatures and some other single variable is doomed to failure, and frankly farcical?

Has he followed the correlation between sunspot activity and climate, first identified by astronomer Edmond Halley in the Eighteenth century?  And the effect of the Dalton and Maunder Minima in the Little Ice Age?  And does he still maintain that atmospheric CO2 is the only significant driver of climate?  Is he aware of the view of some astronomers that the current low levels of solar activity could presage a period of global cooling?

In short, does it ever occur to him that the “consensus” on global warming in 2015 could be about as spurious as the “consensus” on global cooling in 1975?  One of the cardinal errors in both science and (oddly enough – I have observed it myself) in business is to assume that a recent trend will continue in a linear way, causing disaster.  But in astronomy and in climate (and in business) a cyclical model is often a better guide to the future than a straight line.

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