Friday, August 04, 2017

Is the natural variation of climate correlated with solar cycles? And is the future cool?

Global climate is the result of these five variables: Solar variation,  ocean currents, volcanoes, aerosols (i.e. the amount of tiny dust particles in the atmosphere), and finally the greenhouse effect, which is the only variable that humanity has changed and can change.

The favourite argument of the climate change deniers at the moment is this "It is all due to natural variation and climate cycles. Climate always has changed, always will change, it has nothing to do with what we are doing".

At the end of June 2017, Lubecke and Weiss published an interesting article in the Open Atmospheric Science Journal  titled Harmonic Analysis of Worldwide Temperature Proxies for 2000 Years which puts some flesh on the "natural variation" meme. Their work is welcome, because it is easier to discuss a defined proposal than it is to discuss vague assertions.

Lubecke and Weiss analysed a 2000 year earth temperature line, and found that a combination of three sine waves (of year lengths ~1000, ~460, and 190)  matched the temperature record.

Fig 1
Click to enlarge
The upper figure shows the temperature record in blue, and the regular waves in red. The upper red line is created by combining the three sine waves in the lower figure, which they attribute to solar cycles.

As it stands, there is a pretty close correlation between these three putative solar cycles and the earth temperature record over the last 2000 years.

It is up to professional climatologists to look critically at the technicalities of this paper - whether their selection of temperature reconstructions is valid, whether their maths is solid, and whether the cycles they have induced do in fact match records of incoming solar energy.

For now, for the sake of argument, I am going to take their paper at face value, and accept it as evidence  that solar variation is a significant driver of earth climate. It is worth discussing, because the climate change deniers are going to hail it, as is their wont, as the final nail in the coffin of climate alarmism.

Let us look more closely at the later section of the chart. We began burning fossil carbon significantly around 1850. Figure 2 shows the section of Lubecke-Weiss graph after 1500 AD.

Figure 2
We see a peak in 1940, both in their wave construction and in T, but after the 1970s the blue temperature line and the red solar line part company, with T going up and solar going down.
This deviation is well known. Here is a graph from the IPCC on solar activity and temperature (apologies for the fact that the colours are reversed):

Fig 3

It confirms the deviation of T and solar activity in the last few decades, which is consistent with the physics of the situation as the increase in CO2 kicks in.

But the deviation is only recent. What if Lubecke and Weiss are right in their projections, and solar activity does indeed fall to something comparable to the Maunder Minimum of the 17th century? There is other work, on the "solar dynamo" that suggests that this is an accurate prediction.

Feuler and Rahmstorf addressed this question in 2010. They found that a decrease in solar activity on the level of the Maunder Minimum would reduce T by only 0.3*C by 2100, an insignificant reduction of the 3*C increase which continued burning of fossil carbon will impose on the same time scale.

So the "Natural Variation"  and the "Cooling Sun" memes are not an answer to incoming ecological crisis. There is no reasonable alternative but to leave fossil carbon in the ground, and to obtain our energy instead from our solar income.

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