By Javier

So, you still don’t believe small changes in solar activity can significantly affect climate? You know a very cold period during the Little Ice Age coincided with the Maunder Minimum, but you have heard that the Little Ice Age could have had other causes, like volcanoes. You have been told repeatedly that since 1980 solar activity has been decreasing while global temperature has been increasing, so it can’t be the Sun.

Not so fast. There is a vested interest in climate change not being due to the Sun, as the Sun can’t be taxed or prevented from doing what it does. A further problem is that solar physicists have no clue about how the Sun can show centennial or millennial periodicities. As they prefer to talk about what they know, they reject such periodicities, even though we have evidence in cosmogenic records (14C in tree rings and 10Be in ice cores).

And if I tell you that little changes in the Sun have a disproportionate effect on climate you won’t believe me. You shouldn’t believe me. You shouldn’t believe anybody. Science is not about believing. Religion is about believing. So, I propose that you prove to yourself what effect little changes in the Sun have on climate.

You start with solar variability over the Holocene. There are lots of reconstructions, but not all are equally good. You choose Steinhilber et al., 2012 (SAB2012 from now on). It might not be the best, but it is quite good and uses both 14C and 10Be. The isotopes have different pathways. 14C makes it to CO 2 and it is breathed in by trees and deposited in their rings. 10Be makes it to the ice in ice cores partially through a dry deposition pathway associated with dust, but mainly through a precipitation-dependent pathway. As the isotopes have different climatic dependencies, the effect of climate on the reconstruction is minimized by using both.

You can get the article here:

http://www.pnas.org/content/109/16/5967

And you can get the data here:

ftp://ftp.ncdc.noaa.gov/pub/data/paleo/climate_forcing/solar_variability/steinhilber2012.txt

You can choose solar modulation phi (MV) or Total solar irradiance TSI (W/m^2). It is the same for our purpose. Let’s go with Phi (column 4). A plot of this data is:

Figure 1. Steinhilber et al., 2012 solar activity reconstruction for the past 9400 years from Cosmogenic Isotope data.

The date is in years BP (before 1950). The values after 0 BP show contamination from atomic bomb tests so they are higher than they should be. The last trough below -100 MV is the Maunder Minimum.

Now you should run a frequency analysis on the data, but you don’t need to. SAB2012 already provides a Lomb normalized periodogram as figure S16 in the supplemental data here:

http://www.pnas.org/content/pnas/suppl/2012/04/02/1118965109.DCSupplemental/Appendix.pdf

Figure 2. Steinhilber et al., 2012 Lomb normalized periodogram of total solar irradiance (a) and Asian climate record (δ18O) from Dongge cave, China (b). The horizontal line marks the 95% significance level.

SAB2012 noticed the similarity between solar activity and the Asian monsoon frequency analyses, but you want to keep it even simpler. You are going to select the prominent ~ 980-year periodicity. This periodicity or millennial solar cycle was named the Eddy solar cycle by Abreu et al. in 2010. So you build a 980-year sine function with the formula y = sin 2π/980(x) or its Excel equivalent = SIN((2*PI()/980)*x)

Figure 3. 980-year sine function

You need to find the phase shift, or horizontal distance that the function needs to be displaced, to match the solar activity record. It is easy to see that the solar grand minima (SGM) that are producing the 980-yr periodicity are those labeled with arrows in figure 4, so you don’t need to go into a mathematical fit for your purpose. This match requires a 500-year shift in the function.

Figure 4. Solar activity reconstruction and 980-year periodicity match.

This match is further confirmed by a different solar reconstruction that shows the entire Holocene (11,700 years). The additional 2,300 years have not been included in the periodogram from SAB2012, yet the prolongation of the sine wave (figure 5 black wave) identifies two new SGM perfectly aligned with the Eddy cycle (figure 5 arrows).

Figure 5. Vieira et al., 2011 Holocene solar activity reconstruction and the 980-year periodicity. Arrows indicate the two grand solar minima not included in the frequency analysis that clearly belong to the same cycle.

Now that you have the solar 980-year Eddy cycle correctly identified you move to some climatic data to see if solar activity affects climate. To that end you choose the Bond series of ice-rafted debris that is a proxy for iceberg activity in the North Atlantic. The data is available here:

ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bond2001/bond2001.txt

You are interested in:

“1. Figure 2, “a,b,e,e,d,g” Columns 9-10: Age model and stack (“ocean stacked” record) of % HSG from MC52, V29191, MC21, and GGC22 cores [Figure 2, 7th panel]”.

This stack averages different proxies from four cores and is what everybody uses. The Bond series reproduces very well-known Holocene climate features, like the 8.2 kyr event, the Roman Warm Period, the Medieval Warm Period and the Little Ice Age.

You plot it with the 980-year solar cycle. You might want to plot Bond data with the Y axis inverted so high iceberg activity coincides with low solar activity.

Figure 6. Bond et al., 2011 North Atlantic iceberg activity reconstruction and the 980-year periodicity. Both series show an excellent agreement except for an age drift in the Bond series and a period of poor match between ~ 4100-1800 BP.

Given the excellent match, it becomes clear that there is a drift in the data as it gets older. It is small, about ~ 200 years in 11,600 years (~ 1.7 %), and it clearly corresponds to an incorrect age model in the Bond series, since the radiocarbon data is dated to the year through tree rings, because that is how we date very old organic things.

So, the match is excellent except for a period between ~ 4100-1800 BP. What happened then? To clarify the issue, you can look at the power of the Eddy cycle over time. For that you need a 2-dimensional frequency analysis known as a wavelet spectrum. Steinhilber & Beer, 2013 provide one in their figure 1. It can be found here:

onlinelibrary.wiley.com/doi/10.1002/jgra.50210/full

You select the 980-year periodicity band and ignore the rest.

Figure 7. Steinhilber & Beer 2013 wavelet spectrum of solar activity over the past 9400 years.

The 980-year band shows a fall in power over the period ~ 4100-1800 BP. Now you have a possible explanation for the poor Eddy solar cycle-climate match over that period. The Eddy solar cycle had lower power then and couldn’t affect climate as much.

So, what have you shown so far?

There is a 980-year periodicity in solar activity cosmogenic isotope records, known as the Eddy cycle.

This periodicity shows an excellent match with North Atlantic iceberg proxy records, known as the Bond series, except for a period ~ 4100-1800 BP.

The period of poor solar-climate match corresponds to a period when solar activity does not show a strong Eddy cycle, further reinforcing the solar-climate relationship.

What else can you conclude?

Modern global warming corresponds to a period of high Eddy cycle solar activity.

The next peak of the 980-year Eddy cycle extrapolates to ~ 2095. So more solar activity should be coming in the 21st century.

By now you might have finally convinced yourself that the evidence supports a very strong effect of solar variability on climate, without having to “believe” in anybody. The final question is more difficult, so it is better left for the experts.

Why has global temperature been increasing since 1980 while solar activity has been decreasing?

The answer is that solar variability has multiple effects on climate with different time lags. Total Solar Irradiation variability has a direct effect on temperature within 0-2 years of ~ 0.2 °C (Tung & Camp, 2008) for the 11-year solar cycle. This is the effect accepted by all. The stratospheric effect of UV solar variability influences the North Atlantic oscillation that is lagged by 2-4 years (Scaife et al., 2013). Kobashi et al. 2015 describe a 10-40-year lag on Greenland temperature from ice cores that they attribute to the slowdown of the Atlantic Meridional Overturning Circulation and correlates with changes in the wind stress curl in the North Atlantic with a lag of 38 years in solar variability. Several studies correlating changes in tree-ring width and solar variability document a 10-20-year lag (Eichler et al., 2009; Breitenmoser et al., 2012; Anchukaitis et al., 2017).

The existence of multiple lags means that for the full effect of solar variability to be felt on climate there is a delay of ~ 20 years. The delay is due to the recruitment of slower changing atmospheric and oceanic climatic responses.

This means two things:

Changes over the 11-year cycle are too fast to have much impact on climate.

The general decline in solar activity since 1980 has been felt on climate from ~ 2000, and the low solar activity of SC24 should have a maximum effect on climate ~ 2035.

The evidence suggests that solar variability strongly influences climate change. The solar-hypothesis makes very clear predictions that are the opposite of predictions from the CO 2 -hypothesis. Regardless of changes in CO 2 levels and emissions, the world should not experience significant warming for the period 2000-2035, and might even experience some cooling. If the prediction is correct we can assume that the solar contribution to climate is stronger than the CO 2 contribution. Then more warming should take place afterwards.

[Ed. Note: And that is how science should be done! Make a clear testable prediction. Andy did some very minor editing for language clarity.]

Bibliography

Abreu, J. A., Beer, J., & Ferriz-Mas, A. (2010, June). Past and future solar activity from cosmogenic radionuclides. In SOHO-23: understanding a peculiar solar minimum (Vol. 428, p. 287).

Anchukaitis, K. J., Wilson, R., Briffa, K. R., Büntgen, U., Cook, E. R., D’Arrigo, R., … & Hegerl, G. (2017). Last millennium Northern Hemisphere summer temperatures from tree rings: Part II, spatially resolved reconstructions. Quaternary Science Reviews, 163, 1-22.

Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M. N., Showers, W., … & Bonani, G. (2001). Persistent solar influence on North Atlantic climate during the Holocene. Science, 294(5549), 2130-2136.

Breitenmoser, P., Beer, J., Brönnimann, S., Frank, D., Steinhilber, F., & Wanner, H. (2012). Solar and volcanic fingerprints in tree-ring chronologies over the past 2000 years. Palaeogeography, Palaeoclimatology, Palaeoecology, 313, 127-139.

Eichler, A., Olivier, S., Henderson, K., Laube, A., Beer, J., Papina, T., … & Schwikowski, M. (2009). Temperature response in the Altai region lags solar forcing. Geophysical Research Letters, 36(1).

Kobashi, T., Box, J. E., Vinther, B. M., Goto‐Azuma, K., Blunier, T., White, J. W. C., … & Andresen, C. S. (2015). Modern solar maximum forced late twentieth century Greenland cooling. Geophysical Research Letters, 42(14), 5992-5999.

Scaife, A. A., Ineson, S., Knight, J. R., Gray, L., Kodera, K., & Smith, D. M. (2013). A mechanism for lagged North Atlantic climate response to solar variability. Geophysical Research Letters, 40(2), 434-439.

Steinhilber, F., Abreu, J. A., Beer, J., Brunner, I., Christl, M., Fischer, H., … & Miller, H. (2012). 9,400 years of cosmic radiation and solar activity from ice cores and tree rings. Proceedings of the National Academy of Sciences, 109(16), 5967-5971.

Steinhilber, F., & Beer, J. (2013). Prediction of solar activity for the next 500 years. Journal of Geophysical Research: Space Physics, 118(5), 1861-1867.

Tung, K. K., & Camp, C. D. (2008). Solar cycle warming at the Earth’s surface in NCEP and ERA‐40 data: A linear discriminant analysis. Journal of Geophysical Research: Atmospheres, 113(D5).

Vieira, L. E. A., Solanki, S. K., Krivova, N. A., & Usoskin, I. (2011). Evolution of the solar irradiance during the Holocene. Astronomy & Astrophysics, 531, A6.

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