Mayer Hillman’s Viewpoint article on climate change (ibid) is typically apocalyptic of him and contains many false and exaggerated claims.
For a start, he says that the current concentration of carbon dioxide in the atmosphere is greater than it was over a million years ago. This claim can only be based on uncorrected ice core data. It is well known that the gases trapped in snow, which has been compacted into ice sheets, partially escape when the ice core is withdrawn and the pressure on the core is released. Moreover, Professor Murry Salby has carried out research showing that, at the sort of pressures existing in ice sheets at depths dating from hundreds of thousands of years before the present, carbon dioxide can actually be compressed into liquid form and expelled from the base of the ice sheet. In ice cores a million years old, therefore, the level of carbon dioxide present on extraction may be less than 10-15 per cent of that originally trapped.
To put recent climatic changes into their true context it is necessary to look at the climate history of the current interglacial period, or Holocene. There is a roughly 100,000-year cycle of glaciations (commonly called ‘ice ages’, of 80-90,000 years) and relatively warm interglacials (10-20,000 years). We are currently some 15,000 years into the current interglacial. Peak temperatures were reached 9,000-7,000 years ago (the ‘Holocene Optimum’) and, since then, the long-term trend has been downwards at the rate of a quarter to a third of a degree Celsius per thousand years. That may not sound a lot, but temperatures today are some two degrees lower than in the Holocene Optimum.
Superimposed on that long-term downward trend there is a cycle of warming and cooling that lasts around 1,000 years. So, 3,000 years ago there was the Minoan Warm Period, 2,000 years ago the Roman Warm Period, 1,000 years ago the Medieval Warm Period and, today, what has become known as the Modern Warm Period.
In between these warm periods there have been cold periods. Each warm period has been slightly less warm than the previous one, and successive cold periods have been slightly colder. This is inevitable as we head towards the end of the current interglacial and the plunge into the next glaciation. While no one can predict with certainty when this will happen, the general view among solar physicists is that we may have only 800-1,000 years of relatively mild interglacial left.
Our oldest instrumental temperature record only dates from the 17th Century (the Central England Temperature Record) and, for most other countries, from the late 19th Century. The 17th Century was the coldest period during the last thousand years and is associated with an extreme lack of sunspot activity called the Maunder Minimum.
Low sunspot activity causes a reduction in the strength of the ‘solar wind’ of charged particles, which embraces the entire solar system. This in turn leads to a period of global cooling and, although the exact mechanism by which this happens is still the subject of debate, there is empirical data in support of two contributory factors, both in the peer-reviewed literature, from Bucha and Svensmark.
Since the early 18th Century, temperatures have been rising overall, though not at a constant rate. This rise in temperature pre-dates the Industrial Revolution, so cannot have been caused by human emissions of carbon dioxide. In the early 19th Century there was a 30-year period of cooling (the Dalton Minimum) caused by a period of low sunspot activity known as a Grand Minimum. Grand Minima occur every 200-210 years and we are entering another one now, as even NASA accepts.
Periods of cooling, such as the Maunder and Dalton Minima, are not uniformly cold but experience wild changes in weather and climate. This is due to the weak solar wind affecting the path of the jet stream. During warm periods, when the solar wind is strong, the jet stream stays close to the poles and does not meander excessively. This results in a relatively stable climate. In cold periods, by contrast, the jet stream becomes longer and fluctuates wildly. Anyone who has been watching weather forecasts recently may have noticed that the jet stream frequently plunges south from Greenland almost to the Equator, before sweeping north over Africa to Europe. This is what caused last year’s heat wave. Depending on the exact track of the jet stream, it can also bring exceptionally cold air down from the Arctic.
So the claim of climate alarmists that global warming leads to more extreme weather events is actually the opposite of the truth. It is during cool periods, such as the one we are now entering, that weather variability and extreme events become more frequent. We may have around 30 more years of wild weather to look forward to.
The solubility of carbon dioxide in sea water is inversely proportional to temperature. This means that, as sea temperatures rise when the Earth naturally warms, excess carbon dioxide is gassed off into the atmosphere. This is the primary reason for the increase in atmospheric carbon dioxide as the climate recovers from the Maunder Minimum. Man-made emissions are trivial by comparison.
During the 1980s and 1990s, when there was undoubtedly a period of natural global warming on Earth, there was also evidence of global warming on Mars, where its polar ice caps shrank. We can be pretty sure that there are no power stations or SUVs on Mars, so the only common denominator between the two planets is that they are both members of the solar system and embraced by the solar wind. As the late British astronomer Sir Patrick Moore said in response to a question about the cause of climate change, “The Sun, the whole Sun, and nothing but the Sun.”
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