What do sunspots have to do with anything?
To bring us up to date, all the heat Earth gets is from the sun. A couple of posts ago, I explained how changes in Earth’s orbit and the tilt of its axis over years, decades, and centuries result in changes in the amount of heat received and absorbed. That blog concluded with, “It’s the sun, but it’s also sunspots.”
When there are more sunspots, the sun puts out more heat. Sunspots are dark, so this may be counterintuitive, but think of the sunspots as geysers… like Old Faithful. They draw to the surface hot material from inside the sun.
Records of sunspots have been kept by Korean astrologers since about 800 B.C.E. The first Western record is a drawing by a monk, John of Worcester, in 1128 C.E.
Since about 1600 C.E., after the invention of the telescope, detailed records have been kept. It was discovered that the number of sunspots is not constant; it varies in an eleven-year cycle. Superimposed on that is a 90-year cycle. When the 11 and 90-year cycles of high and low sunspot numbers coincide, there will be an unusually large or an unusually small number of sunspots.
Sunspot records from 1600 C.E. have been correlated with two significant weather anomalies: the Maunder Minimum (about 1645-1715 C.E.) and the Dalton Minimum (about 1800-1820 C.E.). During those two cold periods, the number of sunspots dropped significantly—to nearly zero during the Maunder Minimum. Temperatures dropped, too. [Remember: “Correlation does not necessarily imply causation.” There may have been other factors at work.]
The Maunder Minimum is associated with a series of exceptionally cold winters, often called “The Little Ice Age.” The Dalton Minimum has been popularized by “The Year Without a Summer.”
During the Little Ice Age, mean annual temperatures across the Northern Hemisphere were about 0.6 degrees Celsius lower than the thousand-year average. This was enough to expand glaciers in Europe, New Zealand, Alaska, and the Andes. During 1816, The Year Without a Summer, global temperatures were as much as three degrees Celsius lower than average. That was enough to create widespread food shortages, famine, and disease.
Temperatures were generally less than one degree Celsius lower in Western Europe and North America, and were as much as a degree warmer [sic] east of the Urals.
Beginning about 1900, the number of sunspots has been unusually high. This period has been nicknamed the Modern Maximum. It is a fair hypothesis to suggest that global warming is due in part to the increased energy from the sun caused by sunspots. However, since the most recent maximum (2000 C.E.), the number of sunspots has declined dramatically, and we are moving into a “solar minimum.” So far this does not seem to have affected the continuing rise of global mean temperatures. There are many things going on besides sunspots.
A few scientists have predicted, based strictly on sunspot activity, that temperatures on Earth around 2030—2040 may resemble those during the Maunder Minimum. Remember… that’s the “Little Ice Age” period.
That would be bad news, because it would offer a false sense of security with respect to global warming and global climate change, and would allow “climate deniers” to say, “We told you so!” without truly understanding the science. At worst, it could throw Earth into another ice age. Further, as the number of sunspots goes down, the high-ultraviolet radiation from the sun increases (good news for sellers of sun block and for dermatologists). The sun’s heliosphere shrinks, allowing more cosmic rays to reach Earth. But sun block, even SPF 100, won’t stop cosmic rays or the secondary X-rays they produce.
On the other hand, there is already evidence that lower sunspot activity and a shrunken heliosphere may reduce the energy of solar flares, which have been known to interfere with electrical power systems, communication satellites, aircraft radios, cell phone signals, and other electrical systems on Earth. That’s good news.
The sun is the source of all heat that Earth receives. We have seen how changes in Earth’s orbit and the tilt of its axis affect how much energy is received and absorbed. We have seen that the amount of energy coming from the sun is not constant.
The next question is, “What does Earth do with this energy?” That will lead to a discussion of Greenhouse Gasses. We’ll look at that in the next post.
Note: The Year Without a Summer was exacerbated by (some volcanologists say “caused by”) the eruption of Mt. Tambora in 1815. Sulfur dioxide injected into the atmosphere reduced the amount of sunlight that penetrated. We saw similar reductions in sunlight following the eruption of Mt. Pinatubo in 1991.
http://www.eia.gov/todayinenergy/detail.php?id=10571 [2013-03-28 This is an old article, but it has a graph of sunspot activity from 1900—2012 C.E.]
http://www.sws.bom.gov.au/Educational/2/3/6 [2016-11-24 Sunspot numbers by year from 1700 to 2013]
http://data.giss.nasa.gov/gistemp/graphs/ [2016-11-24 Global mean temperature anomaly estimates based on land and ocean data]
http://pubs.usgs.gov/fs/1997/fs113-97/ [Mt Pinatubo 2016-11-22]
http://adsabs.harvard.edu/abs/2007AGUFMPP31E..07S [Mt Tamboro]
Registered Curmudgeon, scientist, skeptic, humanist, and writer.