Guest essay by David Archibald
In reading the solar data, what we are after in the near term is the likely month of minimum for the Solar Cycle 24/25 minimum and likely amplitude of Solar Cycle 25. Of course that quest for truth gets easier as we approach the minimum, at least apparently. Solar Cycle 24 looks like being unusual in being short while being weak and Solar Cycle 25 looks like being a repeat of Solar Cycle 24 in terms of amplitude.
The concept of the Super Grand Solar Deepest Minimum is fashionable again for the moment. There is no sign of that in the data. That said, activity in Solar Cycle 24 was back-loaded and if the solar activity to atmospheric temperature connection is real, the planet’s temperature will be running warmer for a few more years as a consequence of that.
The Modern Warm Period is now in the rear vision mirror though and we have returned to 19th century levels of activity. Warmth and pleasantness are boring; the climate is going to get a lot more interesting. Thus the record cold currently in the northeastern US may become more common.
Figure 1: Hemispheric sunspot area and F10.7 flux 1985 – 2018
Sunspot area equates to the F10.7 flux. The solar hemispheres have different trends in activity which can hold for decades. What causes this is a known unkown in solar science.
Figure 2: Heliospheric Current Sheet Tilt Angle 1976 – 2018
The solar cycle is not over until the heliospheric current sheet flattens. Figure 2 shows that activity has popped out of the wedge shape it has been in pointing to September 2019 as the month of flattening. If this cycle ends up like Solar Cycle 23 that means that the decline will steepen up to get to the same point. The month of flattening, and thus the true change of one cycle to the next, does not necessarily coincide with the month of minimum derived from the F10.7 flux:
Figure 3: Heliospheric Current Sheet Tilt Angle aligned on month of minimum
Solar Cycle 23 was an outlier in terms of length in the modern instrument record. Solar Cycle 24 is tracking along with Solar Cycles 21 and 22 and looks like being 10 years long.
Figure 4: F10.7 Flux and Oulu Neutron Count 1964 – 2018
Figure 4 shows one of the signs that the Modern Warm Period ended in 2006. The Oulu neutron count parted company from the F10.7 flux which it had tracking closely. Something changed in the Sun.
Figure 5: Solar Wind Flow Pressure 1967 – 2018
As Figure 4 showed in the F10.7 flux, solar activity was back-loaded in Solar Cycle 24 with much higher activity after the solar cycle peak. That effect is more pronounced in the solar wind flow pressure which is still stronger, so late in the cycle, than it was prior to the solar cycle peak in 2014. Note the low and chaotic solar wind activity during the 1970s cooling period at the beginning of the instrument record. A break in trend in 2006 is evident at the end of the Modern Warm Period.
Figure 6: F10.7 Flux and Ap Index 1964 – 2018
Geomagnetic activity was back-loaded in Solar Cycle 24. The break in 2006 is quite evident.
Figure 7: F10.7 Flux of Solar Cycles 19 to 24 aligned on month of minimum
It looks like Solar Cycle 24 won’t make it to the average cycle length of the last 300 years of 11.1 years.
Figure 8: Interplanetary Magnetic Field 1966 – 2018
The interplanetary magnetic field (IMF) was flat during the 1970s cooling period but still higher than the average level through Solar Cycle 24. The IMF has been in decline for the last three decades – paralleling the decline in sunspot area are by hemisphere shown in Figure 10 following. Just as the activity in hemispheric sunspot area in Figure 10 has an upper bound, the IMF over the last three cycles has an apparent lower bound shown by the red line. To get to that line by the solar minimum in 2019 will require a rapid decline in activity from here.
Figure 9: Sunspot Area by Hemisphere 1874 – 2018
Because the normal representation of solar activity by sunspot number or F10.7 flux sums the northern and southern hemispheres, that disguises the fact that the hemispheres have different drivers or respond to the same driver differently. As shown in Figure 9, once the hemispheric activity is disaggregated the flatness of activity during the last decades of the Little Ice Age is evident and the break to a higher level of activity from 1933.
Figure 10: Sunspot Area 1985 – 2018
For a sloppy old ball of plasma, the Sun shows a lot of discipline. Activity for both hemispheres has bounced off their respective blue lines above which implies some multidecadal forcing.
Figure 11: Sunspot Area 1874 – 1924
Similarly to Figure 10, there was a four decade period from the late 19th century during which the northern solar hemisphere sunspot area was driven by a consistent multidecadal forcing.
Figure 12: Solar Polar Field aligned on minimum for Solar Cycles 22 – 25
The amplitude of the solar polar field strength at solar minimum is predictive of the amplitude of the next solar cycle. After starting out weak, this activity has been tracking that of the lead up to Solar Cycle 24 and it looks like 25’s amplitude will be much the same. Just as the summing of the activities of the solar hemispheres is a misleading compromise, the month of polar field minimum can have a big departure from the official month of solar cycle maximum as shown in the table following:
There is a case for making the month of heliospheric current sheet flattening the month of solar cycle minimum and the month of polar field minimum as the solar cycle maximum.
Figure 13: GISP2 Be10 Data 40,000 BC to 0 AD
Years ago in comments on WUWT, somebody contributed the observation that climate, in a multidecadal sense, is controlled by the magnetic field from the Sun. The best long term record of that is the Beryllium 10 (Be10) record from the Antarctic ice sheet. Figure 13 shows that there are trends in the Be10 record that last tens of thousands of years. The cold spikes of the Older Dryas and Younger Dryas are associated with spikes in Be10, indicating that a weaker solar magnetic field allowed galactic cosmic rays to flood into the inner planets of the solar system, collide with nitrogen atoms in the upper atmosphere and produce the spikes in the record.
Figure 14: Dye 3 Be10 record 1424 to 1985
If the solar magnetic field causes changes in climate then the warmth of the last eighty years-odd of the Modern Warm Period should be associated with a low in Be10 relative the centuries of the Little Ice Age. Figure 14 shows that that is evident in the Be10 record. The spikes of the Sporer, Maunder and Daltona minima are evident, particularly the ultra-cold decade of the 1690s. And so is the break in activity from the Little Ice Age to the Modern Warm Period in 1933.
Figure 15: aa Index 1868 – 2018
Our longest geomagnetic record as measured by instruments is the aa Index. This also shows the clear breaks at the beginning and end of the Modern Warm Period. The recent peak was 26.9 in September 2015. Activity in Solar Cycle 24 was back-loaded to the second half of the cycle.
Figure 16: Cumulative aa Index against the long term average 1868 – 2018
The changes in activity level associated with the beginning and end of the Modern Warm Period are confirmed by plotting the cumulative aa Index against the long term average of the record.
Figure 17: aa Index plotted against Northern Hemisphere temperature lagged by six years
One of the reasons that this planet is so pleasant to live on is that climate does not instantly respond to changes in solar activity; effects are smoothed and lagged. The correlation between the aa Index and northern hemisphere suggests that the lag correlation peaks at six years.
Figure 18: North Atlantic transect 59N to 800 metres depth
This is a graph prepared by Professor Ole Humlum from his Climate4you site. The diagram was last updated on August 13, 2018 with Argo data to June 2018. The six year lag is hard to tease from the modern temperature record where it is clouded by circulation oscillations. But there is a calorimeter covering 70% of the Earth’s surface which is not affected so much by things that happen in the atmosphere. Figure 18 shows a lag of eight years from the end of the Modern Warm Period to lower temperatures in the North Atlantic.
Figure 19: Average temperature along 59 N, 30-0W, 0-800m depth
This area corresponds to the main part of the North Atlantic current. This is also a graph prepared by Professor Ole Humlum from his Climate4you site. The diagram was last updated on August 13, 2018 with Argo data to June 2018. Temperature started trending down from the end of the Modern Warm Period in 2006 but really dived once the eight year lag kicked in during 2014.
Figure 20: 800,000 years of Antarctic CO2 data relative to plant growth response
Some people have been tearful recently because atmospheric carbon dioxide levels are much higher now than their range over the last 800,000 years as shown by ice core data from Antarctica. For some strange reason they think this is a bad thing when the opposite is true. As the paper Plant responses to low CO2 of the past shows, plant growth has responded to the higher atmospheric carbon dioxide level since the start of the Industrial Revolution. Each 1 ppm increase from here raises plant productivity by 0.3 percent. No wonder world grain production is continuing to rise even though the big increases from genetics are behind us now.
Figure 20 shows the what the amount of plant growth over the last 800,000 years would have been relative to the atmospheric concentration at the time the paper was done of 368 ppm. The current population of the planet of seven billion couldn’t be sustained at the levels of the last 800,000 years. I have helpfully annotated the graphic with zones of relative safety. We are now at the beginning of the safe zone with the current concentration of 408 ppm. Heaven help us when the atmospheric concentration starts falling again as it will when we run out of the fossil fuels and the oceans continue their remorseless 800 year turnover, taking most of our hard-won CO2 down into the Davy Deep where it will be no use to man or beast.
David Archibald is the author of American Gripen: The Solution to the F-35 Nightmare