Exploring the effects of humanly generated factors in the role played by Solar activity in the climate. (by Diego Fdez-Sevilla)
(comments updated 12/05/2014)
It is a matter of debate if the solar activity is a major force driving climatic events independently from any other factor. Having explored in previous posts the synergistic connections that exist between mechanisms involved in climatic events I have looked at the possibility of finding more than one position adopted by confronted scientists being feasible at the same time. Meaning, natural forces are strong enough to differentiate day from night and anthropogenic activities are relevant enough to affect the performance of those forces and the mechanisms associated. Altogether the “correct proposal” would not come from defending the power of each force/effect isolated but what it comes from the combination of them. Like looking at the combined effect of sunlight, a magnifying glass and cloudy/clear skies.
Considering the strong influence that the Sun has in our planet, I have looked for indicators in literature pointing to the existence of “priming effects” from humanly generated factors interacting (enhancing or inhibiting) with the performance of Solar activity in the climate. It is not my intention or the scope of this essay to define the role played by the sun but just to explore the existence of such effects.
After having consulted several sources of information I have seen the difficulties that have persisted throughout time to define the strength and independence of the role played by the sun in the climate. I believe that the origin of such difficulties suggest the existence of an interaction from environmental and anthropogenic factors capable to interfere in the magnitude and format of the effect generated by solar activity in the climate. And, the best way to look into it is by following the historical evolution that it has been taken to explore the role played by the sun in our climate.
For this purpose I have consulted different sources of information. For my attempt I have used information and extracts published by several websites that I believe contain relevant information and references. Follow the appropriate links in order to consult the full body of those and share the credit. Please also feel free to make “constructive comments” either in this blog or in the LinkedIn discussion.
Here I will look into the associations that have been already identified throughout history between solar activity, climate, natural processes in the earth system and anthropogenic factors. And finally, I want to link historical findings, theories and approaches with the scientific results of the Inter-Agency Solar Terrestrial Program from 1996 and the actual positions adopted by institutions such as NASA and NOAA.
Where I stand.
Some of the comments that I have received in LinkeIn about my previous post on the Polar vortex breakdown have aimed to identify solar activity as the major force behind it. Once again it is a two sided question: humanly driven or naturally induced. One position claims that activities linked with human development is everything but innocuous for the environment. And that it has grown unaware of generating systemic effects strong enough to modify, not only the physical state of the ecosystem in which they are carried out (land, water, air and biota) but also with the potential to alter the climate at global scale. The other position postulates that the activities carried out by the human species are not strong enough to trigger changes in a system dominated by natural forces, too powerful to feel or allow the anthropogenic influence in the climate (i.e. Solar activity, geological forces, earth’s tilt and cosmic rays).
The forces behind the polar vortex breakdown, as far as looking for consensus, they are still being discussed. Or at least, the main drivers. There are so many parameters playing at the same time, with synergistic interactions, that it can be found lively debates arguing about individual drivers (solar radiation, ice cover, GHGs, natural variability, …), about miscalculations of feedback interactions and even the lack of reliability in the measurements applied. And sometimes I cannot but feel that there are several scientists being right at the same time, even when they feel that they are in opposite positions. Why do I say that? Because natural processes have never worked in isolation and that’s why evolution has allowed time to be the playground where stars led to rocks and rocks to cells and cells to organisms. Since organisms and environment share the molecules from which both are built the mere existence of each affects the other. Now, who is to point/blame as the main driver when identifying the impact of one over the other? Is the activity of the human species relevant enough to alter a planetary equilibrium? May be not on its own, but it is playing a role in a game which still it is not being fully understood.
Increasing amounts of aerosols and GHGs are affecting the adiabatic processes in the atmosphere. That could well play a role modifying the strength and stability of inter atmospheric cell connections (see previous posts: Climate, “normal variability” or “change”?, “Climate variability and energy balance” and “Met Office. The Recent Storms and Floods in the UK (Feb 2014)”). That could not be a force on its own but enough contribution to create a “priming effect” amplifying (or/and inhibiting) the performance of other natural mechanisms involved such as solar activity, soil weathering, the biotic–abiotic feedback, albedo, variations in ice cover and so on (see previous post Resilience in our models and Resilience in our environment).
The Sun’s activity is a major piece playing a key role in the existence and performance of the environment and also the human species. However, how independent is the effect of the sun in our climate from the influence of other factors?
Connecting climate changes with solar variations throughout historical research.
(Extracts from the website created by Spencer Weart about the history of climate change. Follow the link to consult full body and numbered references http://www.aip.org/history/climate/solar.htm. )
Since it is the Sun’s energy that drives the weather system, scientists naturally wondered whether they might connect climate changes with solar variations. Yet the Sun seemed to be stable over the timescale of human civilization. Attempts to discover cyclic variations in weather and connect them with the 11-year sunspot cycle, or other possible solar cycles ranging up to a few centuries long, gave results that have created a lively debate.
The next crucial question was whether a rise in the Sun’s activity could explain the global warming seen in the 20th century? By the 1990s, there was a tentative answer: minor solar variations could indeed have been partly responsible for some past fluctuations… but could future warming from the rise in greenhouse gases outweigh any solar effects?
In the 1950s and 1960s, instruments on rockets that climbed above the atmosphere managed to measure the Sun’s ultraviolet radiation for the first time. They found that the radiation did intensify during high sunspot years. However, ultraviolet light does not penetrate below the stratosphere. Meteorologists found it most unlikely that changes in the thin stratosphere could affect the layers below, which contain far more mass and energy. Still, the hypothesis of atmospheric influence remained alive, if far from healthy.
A few scientists speculated more broadly. Maybe weather patterns were affected by the electrically charged particles that the Sun sprayed out as “solar wind.” More sunspots throw out more particles, and they might do something to the atmosphere. More indirectly, at times of high sunspot activity the solar wind pushes out a magnetic field that tends to shield the Earth from the cosmic rays that rain down from the universe beyond. When these rays penetrate the upper reaches of the atmosphere, they expend their energy producing sprays of charged particles.
Therefore, more sunspots would mean fewer of these particles. Either way there might be an influence on the weather. Meteorologists gave these ideas some credence.(18*) But the solar wind and ultraviolet carried only a tiny fraction of the Sun’s total energy output. If they did influence weather, it had to be through a subtle triggering mechanism that remained altogether mysterious. Anyway variations connected with sunspots seemed likely to bear only on temporary weather anomalies lasting a week or so (the timescale of variations in sunspot groups themselves), not on long-term climate change.(19) —–
Another study came from a team led by the Danish glaciologist Willi Dansgaard. Inspecting layers of ancient ice in cores drilled from deep in the Greenland ice cap, they found cyclical variations. They supposed the Sun was responsible. For the cycle that they detected, about 80 years long, had already been reported by scientists who had analyzed small variations in the sunspot cycle.(22*) Another cycle with a length of about 180 years was also, the group suspected, caused by “changing conditions on the Sun.” The oscillations were so regular that in 1970 Dansgaard’s group boldly extrapolated the curves into the future. They began by matching their results with a global cooling trend that, as others reported, had been underway since around 1940. The group predicted the cooling would continue through the next one or two decades, followed by a warming trend for the following three decades or so.(23)
The geochemist Wallace Broecker was impressed. He “made a large leap of faith” (as he later put it) and assumed that the cycles were not just found in Greenland, but had a global reach.(24) He calculated that the global cooling trend since around 1940 could be explained by the way the two cycles both happened to be trending down. His combined curve would bottom out in the 1970s, then quickly head up. Greenhouse effect warming caused by human emissions of carbon dioxide gas ( CO2) could come on top of this rise, making for a dangerously abrupt warming.(25)
Later studies failed to find Dansgaard’s cycles globally. If they existed at all, the cause did not seem to be the Sun, but quasi-cyclical shifts in the North Atlantic Ocean’s surface warmth and winds. This was just another case of supposed global weather cycles that faded away as more data came in. It was also one of several cases where Broecker’s scientific instincts were sounder than his evidence. The downturn in temperature since the 1940s, whether due to a variation in the Sun’s radiation or some other natural cause, could indeed change to a natural upturn that would add to greenhouse warming instead of subtracting from it. In fact that happened, beginning in the 1970s.
The 1970s also brought controversial claims that weather data and tree rings from various parts of the American West revealed a 22-year cycle of droughts, presumably driven by the solar magnetic cycle. Coming at a time of severe droughts in the West and elsewhere, these claims caught some public attention.(26*) Scientists were beginning to understand, however, that the planet’s climate system could go through purely self-sustaining oscillations, driven by feedbacks between ocean temperatures and wind patterns. The patterns cycled quasi-regularly by themselves on timescales ranging from a few years (like the important El Niño – Southern Oscillation in the Pacific Ocean) to several decades. That might help to explain at least some of the quasi-regular cycles that had been tentatively associated with sunspots.
All this helped to guarantee that scientists would continue to scrutinize any possibility that solar activity could influence climate, but always with a skeptical eye. If meteorologists had misgivings, most astronomers dismissed outright any thought of important solar variations on a timescale of hundreds or thousands of years. Surface features like sunspots might cycle over decades, but that was a weak, superficial, and short-term effect. As for the main energy flow, improved theories of the nuclear furnace deep within the Sun showed stability over many millions of years. Alongside this sound scientific reasoning there may have been a less rational component. “We had adopted a kind of solar uniformitarianism,” solar physicist John (Jack) Eddy suggested in retrospect. “As people and as scientists we have always wanted the Sun to be better than other stars and better than it really is.”(27)
Aerosols, Particle Coalescence and Nuclei Activity.
In 1975 the respected meteorologist Robert Dickinson, of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, took on the task of reviewing the American Meteorological Society’s official statement about solar influences on weather. He concluded that such influences were unlikely, for there was no reasonable mechanism in sight — except, maybe, one. Perhaps the electric charges that cosmic rays generated in the atmosphere somehow affected how dust and other aerosol particles coalesced. Perhaps that somehow affected cloudiness, since cloud droplets condensed on the nuclei formed by aerosol particles. This was just piling speculation on speculation, Dickinson hastened to point out. Scientists knew little about such processes, and would need to do much more research “to be able to verify or (as seems more likely) to disprove these ideas.” For all his frank skepticism, Dickinson had left the door open a crack. One way or another, it was now at least physically conceivable that changes in sunspots could have something to do with changes in climate. Most experts, however, continued to believe the idea was not only unproven but preposterous. Interest might be piqued when someone reported a new correlation between solar changes and weather, but nobody was surprised when further data and analysis knocked it down.(32*) ——-
In 1976, Eddy tied all the threads together in a paper that soon became famous. He was one of several solar experts in Boulder, where a vigorous community of astrophysicists, meteorologists, and other Earth scientists had grown up around the University of Colorado and NCAR. Yet Eddy was ignorant of the carbon-14 research — an example of the poor communication between fields that always impeded climate studies. He had won scant success in the usual sort of solar physics research, and in 1973 he lost his job as a researcher, finding only temporary work writing a history of NASA’s Skylab. In his spare time he pored over old books. Eddy had decided to review historical naked-eye sunspot records, with the aim of definitively confirming the long-standing belief that the sunspot cycle was stable over the centuries.
Instead, Eddy found evidence that the Sun was by no means as constant as astrophysicists supposed. Especially intriguing was evidence suggesting that during the “Little Ice Age” of the 16th-17th centuries, sky-watchers had observed almost no sunspot activity. People clear back to Herschel had noticed this prolonged dearth of sunspots. A 19th-century German astronomer, G.W. Spörer, had been the first to document it, and a little later, in 1890, the British astronomer E. Walter Maunder drew attention to the discovery and its significance for climate. Other scientists, however, thought this was just another case of dubious numbers at the edge of detectability. Maunder’s publications sank into obscurity. It was only by chance that while Eddy was working to prove the Sun was entirely stable, another solar specialist told him about Maunder’s work.(33*)
“As a solar astronomer I felt certain that it could never have happened,” Eddy later recalled. But hard historical work gradually persuaded him that the early modern solar observers were reliable — the absence of sunspot evidence really was evidence of an absence. Digging deeper, he found the inconstancy confirmed by historical sightings of auroras and of the solar corona at eclipses (both of which reflected activity on the Sun’s surface). Once his attention was drawn to the carbon-14 record, he saw that it too matched the pattern. All the evidence pointed to long-sustained minimums and at least one maximum of solar activity in the past two thousand years. It was “one more defeat in our long and losing battle to keep the Sun perfect, or, if not perfect, constant, and if inconstant, regular. Why we think the Sun should be any of these when other stars are not,” he continued, “is more a question for social than for physical science.” ——
At a 1976 workshop where Eddy first presented his full argument, his colleagues tentatively accepted that solar variability might be responsible for climate changes over periods of a few hundreds or thousands of years.(37) Eddy pressed on to turn up more evidence connecting temperature variations with carbon-14, which he took to measure solar activity. “In every case when long-term solar activity falls,” he claimed, “mid-latitude glaciers advance and climate cools.
Already while Eddy’s sunspot figures were in press, other scientists began to explore how far his idea might account for climate changes. Adding solar variability to the sporadic cooling caused by dust from volcanic eruptions did seem to roughly track temperature trends over the entire last millennium.(39) Peering closer at the more accurate global temperatures measured since the late 19th century, a group of computer modellers got a decent match using only the record of volcanic eruptions plus greenhouse warming from increasing carbon dioxide — but they improved the match noticeably when they added in a record of solar variations. All this proved nothing, but gave more reason to devote effort to the question.(40)———-
Satellite measurements pinned down precisely how solar brightness varied with the number of sunspots. Over a sunspot cycle the energy radiated varied by barely one part in a thousand; measuring such tiny wiggles was a triumph of instrumentation.(48) A single decade of data was too short to support any definite conclusions about long-term climate change, but it was hard to see how such a slight variation could matter much.(49) Since the 1970s, rough calculations on general grounds had indicated that it should take a bigger variation, perhaps half a percent, to make a serious direct impact on global temperature. However, if the output could vary a tenth of a percent or so over a single sunspot cycle, it was plausible to imagine that larger, longer-lasting changes could have come during the Maunder Minimum and other major solar variations. That could have worked a real influence on climate.———
The proposed mechanism roughly resembled the speculation that Dickinson had offered, with little confidence, back in 1975. It began with the fact that in periods of low solar activity, the Sun’s shrunken magnetic field failed to divert cosmic rays from the Earth. When the cosmic rays hit the Earth’s atmosphere, they not only produced carbon-14, but also sprays of electrically charged molecules. Perhaps this electrification promoted the condensation of water droplets on aerosol particles? If so, there was indeed a mechanism to produce extra cloudiness. A later study of British weather confirmed that at least regionally there was “a small yet statistically significant effect of cosmic rays on daily cloudiness.”(53)——–
Whatever the exact form solar influences took, most scientists were coming to accept that the climate system was so unsteady that many kinds of minor external change could trigger a shift. It might not be necessary to invoke exotic cosmic ray mechanisms, for the system might be sensitive even to the tiny variations in the Sun’s total output of energy, the solar constant. The balance of scientific opinion tilted. Many experts now thought there was indeed a solar-climate connection.(55)—-
Rough limits could now be set on the extent of the Sun’s influence. For average sunspot activity decreased after 1980, and on the whole, solar activity had not increased during the half-century since 1950. As for cosmic rays, they had been measured since the 1950s and likewise showed no long-term trend. The continuing satellite measurements of the solar constant found it cycling within narrow limits, scarcely one part in a thousand. Yet the global temperature rise that had resumed in the 1970s was accelerating at a record-breaking pace, chalking up a total of 0.8°C of warming since the late 19th century. It seemed impossible to explain that using the Sun alone, without invoking greenhouse gases. “Over the past 20 years,” a group reviewing the data reported in 2007, “all the trends in the Sun that could have had an influence on the Earth’s climate have been in the opposite direction to that required to explain the observed rise in global mean temperatures.” It was a stroke of good luck that the rise of solar activity since the 19th century halted in the 1960s. For if solar activity had continued to rise, global temperatures might have climbed slightly faster — but scientists would have had a much harder job identifying the part play by greenhouse gases in a global warming.
The most advanced computer modelling groups did manage to reproduce the faint influence of the sunspot cycle on climate. Their calculations showed that since the 1970s that influence had been overtaken by the rising effects of greenhouse gases. The modellers got a good match to maps of the climate changes observed over the past century, but only if they included the effects of the gases, and not if they tried to attribute it all to the Sun. For example, if they put in only an increase of solar activity, the results showed a warmer stratosphere. Adding in the greenhouse effect made for stratospheric cooling (since the gases trapped heat closer to the surface). And cooling was what the observations showed.(57*)—————
Public positioning in 1996 and in actual times.
1996, Proceedings of the Symposium D0.1 of COSPAR Scientific Commission D which was held during the Thirty-First COSPAR Scientific Assembly, Birmingham, United Kingdom.
A symposium presenting the scientific results of the Inter-Agency Solar Terrestrial Program was convened by COSPAR commission D at the 31st Plenary meeting in Birmingham, UK, in July, 1996. RESULTS OF THE IASTP PROGRAM. Volume 20, Issues 4-5. 14-21 July, 1996. http://www-ssc.igpp.ucla.edu/IASTP/43/
What do we really know about the Sun-climate connection?
Eigil Friis-Christensen and Henrik Svensmark
Scientific discussions about the possible role of solar activity variations on climate have suffered from the lack of a precise physical mechanism that could account for the vast number of reported correlations. In particular it has not been possible to identify unambiguously neither the important solar activity parameter nor the primary climatic parameter in such relationships.
Solar activity variations have traditionally been associated with the sunspot number although it is well known that solar activity may not be described by a single number. In particular it has been difficult to find a good representation of the long-term variations of solar activity. That solar cycle relationships cannot just be extrapolated to represent long-term behaviour is demonstrated by the relative variations of the sunspot number and the geomagnetic activity index, aa. Although aa is an index specifically associated with the fluctuations in the terrestrial magnetic field, it does represent the result of the continuous interaction between the geomagnetic field and the solar wind, and hence some form of solar activity. In Figure 5 is shown a comparison between the aa-index and the sunspot number R since 1868 when systematic geomagnetic recordings allowed the derivation of the aa-index. The aa-index does show the 11-year cycle but two main differences between R and aa are clearly noticeable. Firstly, the individual cycles are very different with the aa record normally displaying several maxima whereas the sunspot record has only one dominant maximum in each cycle. The second fundamental difference is the different long-term variation seen in aa and R, in particular in the level at solar activity minima. This clearly demonstrates that some long-term change in the solar wind has taken place during this century which is not reflected in the sunspot number at solar minima.
The formation and radiative effect of clouds is one of the major uncertainties in climate modeling (Houghton et al., 1995). Due to the large radiative effect of clouds, any insufficiency in the parameterization of clouds will introduce major uncertainties in the results of the climate models. Recent results have indicated strong correlations between the total cloud cover and the cosmic ray flux, indicating that this could be the missing link between solar activity variations and climate changes. If this relationship can be confirmed and understood, a major obstacle in our understanding of natural climate variations may be removed and our chances of a credible estimate of the effects of manmade greenhouse gases could be significantly improved.
2012. NASA. The Effects of Solar Variability on Earth’s Climate:
A Workshop Report (2012)http://science.nasa.gov/science-news/science-at-nasa/2013/08jan_sunclimate/
On September 8-9, 2011, experts in solar physics, climate models, paleoclimatology, and atmospheric science assembled at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado for a workshop to consider the Sun’s variability over time and potential Sun-climate connections.
“In recent years, researchers have considered the possibility that the sun plays a role in global warming. After all, the sun is the main source of heat for our planet. The NRC report suggests, however, that the influence of solar variability is more regional than global.”
“Some attendees stressed the need to put sun-climate data in standard formats and make them widely available for multidisciplinary study. Because the mechanisms for the sun’s influence on climate are complicated, researchers from many fields will have to work together to successfully model them and compare competing results.”
Hal Maring, a climate scientist at NASA headquarters who has studied the report, notes that “lots of interesting possibilities were suggested by the panelists. However, few, if any, have been quantified to the point that we can definitively assess their impact on climate.” Hardening the possibilities into concrete, physically-complete models is a key challenge for the researchers.
Finally, many participants noted the difficulty in deciphering the sun-climate link from paleoclimate records such as tree rings and ice cores. Variations in Earth’s magnetic field and atmospheric circulation can affect the deposition of radioisotopes far more than actual solar activity. A better long-term record of the sun’s irradiance might be encoded in the rocks and sediments of the Moon or Mars. Studying other worlds might hold the key to our own.
2013. NOAA. THE SUN AND SUNSPOTS.
Can an increase or decrease in sunspot activity affect the Earth’s climate?(http://www.crh.noaa.gov/fsd/?n=sunspots)
The jury is still out on how much sunspots can (or do) affect the Earth’s climate. Times of maximum sunspot activity are associated with a very slight increase in the energy output from the sun. Ultraviolet radiation increases dramatically during high sunspot activity, which can have a large effect on the Earth’s atmosphere. From the mid 1600s to early 1700s, a period of very low sunspot activity (known as the Maunder Minimum) coincided with a number of long winters and severe cold temperatures in Western Europe, called the Little Ice Age. It is not known whether the two phenomena are linked or if it was just coincidence. The reason it is hard to relate maximum and minimum solar activity (sunspots) to the Earth’s climate, is due to the complexity of the Earth’s climate itself. For example, how does one sort out whether a long-term weather change was caused by sunspots, or maybe a coinciding El Nino or La Nina? Increased volcanic eruptions can also affect the Earth’s climate by cooling the planet. And what about the burning of fossil fuels and clear cutting rain forests? One thing is more certain, sunspot cycles have been correlated in the width of tree ring growth. More study will be conducted in the future on relating sunspot activity and our Earth’s climate.