On Reading The Little Ice Age

Posted by jns on March 11, 2009

Earlier this year I read the book Brian Fagan, The Little Ice Age : How Climate Made History 1300 – 1850, by Brian Fagan (New York : Basic Books, 2000; 246 pages). He takes a close look at the relatively cool period between the “Medieval Warm Period” and the current warming period, and considers in careful but fascinating detail the ways that global climate change affected European society and culture. I thoroughly enjoyed it. I think he did an excellent job assembling all of his facts and dates and locations and keeping them well sorted out and in line with his thesis. I gave it high marks in my book note.

Anyway, here’s an excerpt that interested me. This was one of his many entertaining and enlightening asides, this one a nicely done short history of sunspots.

Sunspots are familiar phenomena. Today, the regular cycle of solar activity waxes and wanes about every eleven. years. No one has yet fully explained the intricate processes that fashion sunspot cycles, nor their maxima and minima. A typical minimum in the eleven-year cycle is about six sunspots, with some days, even weeks, passing without sunspot activity. Monthly readings of zero are very rare. Over the past two centuries, only the year 1810 has passed without any sunspot activity whatsoever. By an measure, the lack of sunspot activity during the height of the Little Ice Age was remarkable.

The seventeenth and early eighteenth centuries were times of great scientific advances and intense astronomical activity. The same astronomers who observed the sun discovered the first division in Saturn’s ring and five of the planet’s satellites. They observed transits of Venus and Mercury, recorded eclipses of the sun, and determined the velocity of light by observing the precise orbits of Jupiter’s satellites. Seventeenth-century scholars published the first detailed studies of the sun and sunspots. In 1711, English astronomer William Derham commented on “great intervals” when no sunspots were observed between 1660 and 1684. He remarked rather charmingly: “Spots could hardly escape the sight of so many Observers of the sun, as were then perpetually peeping upon him with their Telescopes…all the world over.” Unfortunately for modern scientists, sunspots were considered clouds on the sun until 1774 and deemed of little importance, so we have no means of knowing how continuously there were observed.

The period between 1645 and 1715 was remarkable for the rarity of aurora borealis and aurora australis, which were reported far less frequently than either before or afterward. Between 1645 and 1708, not a single aurora was observed in London’s skies. When one appeared on March 15, 1716, none other than Astronomer Royal Edmund Halley wrote a paper about it, for he had never seen one in all his years as a scientist–and he was sixty years old at the time. On the other side of the world, naked eye sightings of sunspots from China, Korea, and Japan between 28 B.C. and A.D. 1743 provide an average of six sightings per century, presumably coinciding with solar maxima. There are no observations whatsoever between 1639 and 1700, nor were any aurora reported.