Scientists Link Quiet Sun & Cold Winters
Asking the somewhat obvious question, “are cold winters in Europe associated with low solar activity?” a group of scientists have announced that the answer is yes. While this may seem unsurprising, the finding is another indication that Earth's climate is not simply driven by greenhouse gas emissions. Even so, some scientists are only grudgingly accepting the finding, cautioning that this only applies in the central UK and refusing to admit that the Sun could affect global mean temperatures as well. Still, the researchers found that average solar activity has declined rapidly since 1985 and cosmogenic isotopes suggest a possible return to Maunder minimum conditions within the next 50 years. This could be a sign that climate science is starting to recover from its CO2 fixation.
Writing in Environmental Research Letters, Mike Lockwood et al. have verified that solar activity does seem to have a direct correlation with Earth's climate—at least in the central UK. The reason that the scope of the study is limited to that area, or at most Europe, is that it is one of the few regions that there is a reliable, continuous temperature record going back to the Little Ice Age. The authors explain their work:
Lower winter temperatures were common in Europe during the second half of the 17th century, famously allowing frost fairs to be held on the Thames in London before riverine developments increased the flow rate. These cold winters coincided with the Maunder minimum in solar activity when the Sun remained virtually free of sunspots for almost 50 years. However, establishing that this was not just a chance occurrence requires that the relationship continue to hold over a long interval, such that cold European winters become less frequent when solar activity is high and then more common again when solar activity falls. Various indicators show that during the recent minimum of the 11 year sunspot cycle, the Sun has been quieter than at any time in the previous 90 years. This yields an opportunity for a better test of the relationship between solar activity and cold European winters. To do this, we require two long and homogeneous time series: one which quantifies solar outputs relevant to seasonal/regional climate and the other relevant to European winter temperatures. We here use the Central England temperature (CET) data set which is the world's longest instrumental record of temperature and extends back to 1659, at the start of the Maunder minimum.
What is different about the CET data and other historical records is that it consists of direct temperature readings, not proxy data, as far back as 1850. “We show that cold winter excursions from the hemispheric trend occur more commonly in the UK during low solar activity, consistent with the solar influence on the occurrence of persistent blocking events in the eastern Atlantic,” the authors state. It is proposed that the reason for the cooling is the blocking of tropospheric jet streams, which help to maintain Europe's temperate climate. “Clearly any solar control is subtle and far from being the only factor causing variability,” they report. “We stress that this is a regional and seasonal effect relating to European winters and not a global effect.”
Regional or not, 2010 was still darned cold.
It is interesting that when claims are made for CO2 emissions acting through a multitude of murky and ill-defined feedback mechanisms are made, climate scientists quickly credit carbon dioxide with control of Earth's climate. When a link to solar activity is found, the possibility that it acts by causing jet stream flows to be rerouted is used as a way to diminish the Sun's importance to climate. It seems irrational to say that the Sun only affects the climate of Europe.
In The Resilient Earth we quoted Thomas Jefferson, himself a scientist and naturalist. In response to remarks made by the Comte de Buffon, Jefferson said that it was foolish to think “that nature is less active, less energetic on one side of the globe than she is on the other ... as if both sides were not warmed by the same genial sun.” In the face of this recent work, it may well be that other mechanisms, which amplify the effects of solar variation, await discovery in other parts of the world. In fact, it is possible that the cited mechanism is not the primary reason for the link to the Sun, even in the UK.
There was a time when climatologists credited the Sun with a much more dominant role in earthly climate. Some of the ups and downs of solar forcing has been presented in a perspective on the Lockewood et al. paper, written by Rasmus E. Benestad, of the Norwegian Meteorological Institute in Oslo, Norway. He describes the problems in past studies this way:
One notorious problem with many previous studies was that relationships established over the calibration interval subsequently broke down. There was a period in the mid-20th century when little work was done on solar activity and climate, but solar activity was considered a real forcing factor before 1920. With the advent of frontal theory, orbital forcing theory, and stronger awareness of the implications of enhanced greenhouse gas concentrations, the support for solar forcing seemed to have diminished in the climatology community by the mid-20th century. But non-stationary relationships, the chaotic character of climate, weak effects, and lack of a physical understanding behind such a link, can also explain the low support for solar forcing at that time.
Notice that non-stationary data are again at the root of analytical problems with climate data. That, plus non-linearity caused by the chaotic nature of Earth's climate system, continue to cause headaches for researchers to this day (see “Econometrics vs Climate Science” and “Climate Science's Dirtiest Secret”). Little wonder that climate scientists turned to the easier to measure growth of CO2 levels in the atmosphere as the proximate cause of global warming. Undaunted, Lockwood et al. have proceeded with analyzing the available data.
Measuring Solar Activity in the Past
To quantify solar activity, the researchers used annual means of the open solar magnetic flux, FS, which they called “the total magnetic flux dragged out of the Sun by the solar wind flow.” This derivation of FS makes use of the fact that different measures of the fluctuation level in Earth's magnetic field correlate strongly with different combinations of solar wind parameters. Using a combination of these parameters allowed the reconstruction of past variations, including that in FS. Comparison with satellite observations shows that this method is extremely reliable, even during the current exceptional solar minimum.
FS is highly anticorrelated with cosmic ray fluxes. It has been shown that cosmic rays are regulated by the activity of the Sun and display an inverse relationship with total solar irradiance (TSI), though with a lag of 1 year. These correlations are at the center of a relationship between TSI and solar-modulated cosmogenic isotopes, which is generally assumed in palaeoclimate studies.
Many isotopes are generated by the interaction of cosmic rays with atoms of the atmosphere, hydrosphere, or the top layers of the lithosphere. These cosmogenic isotopes includes stable isotopes such as 3He, but most of the isotopes in question are radioactive. These include 10Be, 14C, 26Al, 36Cl, 41Ca and 129I. Levels of these isotopes can be used as proxy data for cosmic ray levels. The relationship of FS, derived from geomagnetic observations, with TSI and galactic cosmic ray fluxes (GCRs) over the past several decades is shown in Figure 1 from the paper, shown below.
The relationship of open solar flux with total solar irradiance and galactic cosmic ray fluxes.
The second figure shows the seasonal December/January/February (DJF) means, TDJF, of the CET record, which is representative of a roughly triangular area between Lancaster, London and Bristol. Annual means from the HadCRUT3v compilation of Northern Hemisphere observations, which is available for 1850 onwards, were extend these data back to 1659 using an ensemble of 11 reconstructions based on a wide variety of proxies. The data after 1974 were adjusted for urban warming by comparing the modern data from long-established stations with data sequences from stations in rural areas. To identify regional effects, the average temperature for the whole Northern Hemisphere was compared with the regional data.
Variations since the mid-17th century of temperatures and FS.
After much statistical analysis, including detrending to compensate for the nonstationarity of the data, the researchers reached the conclusion that, at least in Great Britain, an inactive Sun results in colder winters. In the authors' words: “The results presented in section 4 allow rejection of the null hypothesis, and hence colder UK winters (relative to the longer-term trend) can therefore be associated with lower open solar flux (and hence with lower solar irradiance and higher cosmic ray flux).” Those interested in the gory statistical details should refer to the paper.
In his perspective article, Benstad notes that Crooks and Gray (2005) identified a solar response in a number of atmospheric variables, and Labitske (1987), Labitske and Loon (1988) and Salby and Callagan (2000) provided convincing analyses suggesting that the zonal winds in the stratosphere are influenced by solar activity. Furthermore, Baldwin and Dunkerton (2001) provided a tentative link between the stratosphere and the troposphere (perhaps not so tentative, see “Atmospheric Solar Heat Amplifier Discovered”). Still, for climate science to back away from AGW driven by human CO2 emissions is too bold a leap. It seems that many climate scientists—particularly those in thrall of computer climate models—do not like the idea of returning to the use of empirical data, the bedrock of all the hard sciences.
“The physical picture they provide is plausible, yet empirical relationships between solar activity and any of the indices describing the north Atlantic oscillation, the Arctic oscillation or the polar vortex are regarded as weak.,” concluded Benstad, “my impression is nevertheless that the explanation provided by the Lockwood et al study reflects real aspects of our climate.” Trying to maintain a modicum of scientific open-mindedness, he added, “Thus, it is an example of incremental scientific progress rather than a breakthrough or a paradigm shift.” Perhaps not a breakthrough, but a return to an older, more correct path.
Studies of cosmogenic isotopes show that the Sun has been exceptionally active during recent decades, compared to the previous 11,000 years. The recent solar maximum has persisted for longer than most previous examples in the cosmogenic isotope record and many scientists suspect the period of heightened solar activity is ending. “Recent activity has been abnormally high for at least 8 cycles,” state J. A. Abreu et al., in a 2008 paper. “We find that it is only expected to last for a further 15–36 years, with the more reliable methods yielding shorter expectancies, and we therefore predict a decline in solar activity within the next two or three cycles.” Indeed, Lockwood and others think that a new minimum may be in store.
In previous work, published in the Proceedings of the Royal Society, Lockwood stated: “Solar outputs during the current solar minimum are setting record low values for the space age. Evidence is here reviewed that this is part of a decline in solar activity from a grand solar maximum and that the Sun has returned to a state that last prevailed in 1924.” Citing this work, Lockwood et al. make a cautious prediction regarding future winters.
Average solar activity has declined rapidly since 1985 and cosmogenic isotopes suggest an 8% chance of a return to Maunder minimum conditions within the next 50 years: the results presented here indicate that, despite hemispheric warming, the UK and Europe could experience more cold winters than during recent decades.
So will the Sun turn somnolent, lessening the amount of radiant warmth it showers on Earth? Could another Little Ice Age be in our immediate future? Predictions are for a less active Sun during the upcoming Cycle 24, but only time will tell. We have had decades of near hysterical warnings about rising temperatures, all of which may be negated by the unpredictable fluctuations of our local star. It will be interesting to see how long it takes climate science to change its doomsday predictions for the next several decades. Indeed, it has taken almost half a century for climate science to dig itself into its current hole, it may take as long to dig itself back out.
Be safe, enjoy the interglacial and stay skeptical.