Year Without a Summer

A weak solar maximum, a major volcanic eruption, and possibly even the wobbling ofthe Sun conspired to make the summer of 1816 one of the most miserable ever recorded.

by Willie Soon and Steven H.Yaskell

MayJun13_22 4/11/03 5:26 PM Page 13

Mercury -

The year 1816 is still known toscientists and historians as “eigh-teen hundred and froze to death”or the “year without a summer.” Itwas the locus of a period ofnatural ecological destruction not

soon to be forgotten. During that year, theNorthern Hemisphere was slammed withthe effects of at least two abnormal butnatural phenomena. These events weremysterious at the time, and even today theyare not well understood.

First, 1816 marked the midpoint of oneof the Sun’s extended periods of low mag-netic activity, called the Dalton Minimum.This particular minimum lasted from about1795 to the 1820s. It resembled the earlierMaunder Minimum (about 1645-1715)

that was responsible for at least 70 years ofabnormally cold weather in the NorthernHemisphere. The Maunder Minimuminterval is sandwiched within an even betterknown cool period known as the Little IceAge, which lasted from about the 14ththrough 19th centuries.

But the event that most severely shaped1816’s cold phenomena was the cata-strophic eruption the previous year ofTambora on the island of Sumbawa, inmodern-day Indonesia. The ash clouds andsulfur aerosols spewed by this volcano werewidespread, chilling the climate of theNorthern Hemisphere by blocking sunlightwith gases and particles.

A third factor also could have played arole. During both the Dalton and the

Maunder minima, the Sun shifted its placein the solar system — something it doesevery 178 to 180 years. During this cycle, theSun moves its position around the solarsystem’s center of mass. This particular trickof gravity is known as “inertial solarmotion.” Scientists have not yet confirmedwhether or not inertial solar motion affectsEarth’s climate directly, but it remains apossibility.

The combined influences of the Sun’schanges in magnetism, a major volcaniceruption, and possibly even the wobbling ofthe Sun’s position were responsible forfamine, drought, and destructive snows andrains in the Northern Hemisphere in 1816.Diary entries and newspaper accountsabound of the unusual spring and summer

Dolton Minimum(c. 1795 - 1823)

Dolton Minimum(c. 1795 - 1823)

Mounder Minimum(c. 1645 – 1715)

1650

200

150

100

50

01700 1750 1800 1850 1900 1950 2000

Dolton Minimum(c. 1795 - 1823)

Mounder Minimum(c. 1645 – 1715)

This graph shows the annual count of sunspots from 1610 to 2000. Sunspot cycles average 11 years in length. But notice the deep drop in sunspot numbers dur-ing the Maunder and Dalton minima.Both minima were associated with global cooling.Courtesy of Tom Ford.Data courtesy of David Hathaway (NASA/MSFC).

Sunspots are manifestations of solar magnetic activity. In general, the more sunspots there are, the more active the Sun is. Ironically, the Sun is usually brighterwhen a large number of sunspots mar its visible surface. Courtesy of William C. Livingston (Kitt Peak National Solar Observatory).

MayJun13_22 4/11/03 5:26 PM Page 14

- Mercury

cold. People even noted the sky’s abnormalcolor, the large sizes of sunspots, and othercuriosities. Because most people in theNorthern Hemisphere were subsistencefarmers, crop failure meant not only hard-ship, but often death. Crop yields in parts ofAmerica and Europe sank dangerously lowfor a year, causing eyes to focus on a blotchySun and an angry God — or both.

A Miserable SummerThe people who survived the drought andcold would long after refer to 1816 as“eighteen hundred and froze to death.” Sleetfell in the Northeast United States, andsnowdrifts remained 2 feet deep in latespring. In Franconia, New Hampshire, 88-year-old physician Edward Holyoke, an

amateur astronomer and meteorologistwho kept detailed weather records for 80years, wrote on June 7: “exceeding[ly] cold.Ground frozen hard, and squalls of snowthrough the day. Icicles 12 inches long in theshade at noon day.”

Nobody could recall such a cold spring.Sheep froze in meadows and small birdswere “easily caught by reason of the cold” orwere found dead in fields. Massachusettsphysician William Bentley wrote on June12: “in few seasons have we heard more bit-ter complaints against cold weather thansince June has come in.” Others recordedkiller droughts and a strange, tepid drynesswafting on northwest winds. A vividimpression of that summer in the NortheastUnited States appeared in verse:

The trees were all leafless, the mountains were brown

The face of the country was scathed with a frown

And bleak were the hills, and the foliage sere

As had never been seen at that time of the year.

A certain degree of normalcy returnedfor part of the summer. In some coastalareas, the weather was “bland and agreeable,if humid.” Spurting vegetable growth couldfool anyone: even astute long-time weatherobservers like Holyoke described June 17 toAugust 17 as “uniformly fine.” He wrote in aconfident hand that the crop outlook wasbetter “than could have been anticipated.”

These X-ray images of the Sun from the Japanese/American Yohkoh satellite demonstrate solar activity waxing and waning between the sunspot maximain 1991 and 2000.The images, taken at 1-year intervals, show changes in the corona.The visible “surface” of the Sun, the photosphere, is so cool (about6000° C) that it barely emits X-rays, so it appears black in these images. Courtesy of ISAS and NASA.

MayJun13_22 4/11/03 5:26 PM Page 15

Mercury -

But then the cold struck again. OnAugust 21, Holyoke wrote in a tenser hand,recording the frosts and snows that killedoff the meager bean and corn crop. Thedifference between August 17 and 21 waslike summer compared with winter. Thefields were “as empty and white as October.”This particular damaging frost affectedareas from southern Canada to NorthCarolina. Cold struck again on September11, and people tended fields as if dressed forDecember. In an age characterized by back-breaking labor, the “poverty year,” as 1816was called by some, was a harrowing ordeal.

The bad weather wasn’t confined toNorth America. The summer weather inparts of Europe was so bad that it remindedpeople of November. On June 16, MaryWollstonecraft Shelley noted that theweather at Lake Geneva turned abruptlyfrom dry and beautiful to lashing rain, withhowling winds and vicious lightningstorms. Shelley was spending the “cold andrainy” summer in Switzerland with various

literati. Most were confined indoors onstormy June 22, where rounds of ghoststories ensued. They pledged to record thesefables on paper, and Mary Shelley was thefirst to prevail (by 1818). As a fruit of herlabors, we have the Gothic chiller Franken-stein: Or, the Modern Prometheus.

A Strange Solar MaxFirst, let’s focus on how the Sun made 1816a bad year. The Dalton and Maunderminima were extended periods of very weaksolar activity, spanning about 25 years and70 years, respectively. Records from theseperiods show far fewer sunspots than nor-mal, meaning the Sun’s magnetic activitywas very weak during those years. Eventhough the Sun is covered by relatively fewdark sunspots when it is not magneticallyactive, it also has fewer bright regions,known as plages and faculae. Sustainedperiods of weak magnetic activity make theSun slightly dimmer, so Earth receives lesssolar light energy.

Scientists have recently reconstructedthis weak magnetic activity by measuringvarious chemical isotopes in tree rings, forexample, and matching them to weatherand temperature oddities. Cosmic raystransmute nitrogen-14 in Earth’s upperatmosphere, creating the radioactiveisotope carbon-14. In the 1970s, solarastronomer John Eddy of the High AltitudeObservatory in Boulder, Colorado showedthat carbon-14 concentration in annual treegrowth rings is higher when fewer sunspotsblemish the Sun’s surface.

There’s an astronomical explanation forthis linkage. Strong magnetic activity on theSun is passed on to the solar wind — astream of protons and helium nuclei flow-ing outward from the Sun at high speed. Astrong magnetic field in the solar windshields Earth from cosmic rays. Becausefewer cosmic rays collide with Earth, lesscarbon-14 forms in the atmosphere. Butwhen solar magnetism is weak, more galac-tic cosmic rays can reach Earth and make

From his Monticello home in Virginia, Thomas Jefferson recorded the severe weather of 1816 in his weather diary. Jefferson was just one of manyobservers who recorded unusually cold weather during the summer of 1816.And the strange weather was not confined to eastern North America. Badweather was recorded all over the world.The cold and rainy summer in Switzerland even inspired Mary Wollstonecraft Shelley to write Frankenstein.Courtesy of the Jefferson papers, Manuscript Division, Library of Congress, Gerard W. Gawalt.

MayJun13_22 4/11/03 5:26 PM Page 16

- Mercury

more carbon-14. The carbon-14 in turncombines with oxygen molecules in theatmosphere to make the heavy version ofcarbon dioxide that will ultimately beincorporated into the cellulose of growthrings of living trees.

Suspicious 19th-century eyes turnedupward at an angry God, and at the Sun.Fingers pointed to a spotty Sun as theculprit for the strange and unpredictableweather. In 1816 sunspots were so large thatthey could be seen without telescopes. Onereport notes the presence of particularlylarge sunspots from May 3 to 10, and againon June 11, when a dry fog due toTambora’s effects reddened and dimmedthe disk of the Sun. This reddened condi-tion acted as a solar filter and made thelarge sunspots stand out easily, even tounaided eyes. The sunspots made quite animpact on the average person, who “at thetime believed that the large spots appearingon the Sun’s disk lessened the number ofrays of light and consequently the earth was

to that extent cooler than usual,” wroteSidney Perley in the 1891 book HistoricStorms of New England.

The dark spots certainly dimmed sun-light, but the spots alone couldn’t explainthe unseasonable cold and snow. If sunspotswere the only culprit, the cooling effectsfrom the reduced sunlight should havecome and gone through each 27-day solarrotation. In addition, large sunspots seldomlast longer than a month, which wouldotherwise be necessary to explain theextended period of cooling.

Ironically, 1816 occurred around themaximum of the Sun’s 11-year sunspotcycle. But the sunspot groups counted in1816 amounted to a mere 35, as opposed toabout 100 for a normal year around solarmaximum. This is about the lowest sunspotmaximum ever recorded, so astronomerscall it a “weak solar maximum.” A person onthe street might have accused the Sun ofcausing the bad weather, but sunspots aloneweren’t doing the chilling and killing. We

must look deeper for the culprit and rightinto the Sun’s magnetic cycles. The cause ofthe Sun’s magnetic activity cycles is still apressing research topic.

Inasmuch as 1816 was a weak solar max-imum, the question lingers of how muchthe dimmed Sun affected global cooling.But compared with Tambora’s eruption, theSun played just a minor role in coolingEarth, at least for that year. Still, the Sun’scooling effects could have gradually begunlong before 1816.

Tambora’s FuryTambora’s eruption activity peaked on April10 and 11, 1815. Approximately 90,000people perished on and around SumbawaIsland in the Java Sea — many from faminein the eruption’s aftermath. Tambora’seruptive force, mortality, and atmosphericimpact exceeded anything like it on Earth inthe past 10,000 years. The catastrophiceruption was so powerful that it shearedTambora nearly in half, from 4,300 to 2,850

While not nearly as violent as Tambora’s 1815 eruption, the June 1991 eruption of Mount Pinatubo in the Philippines devastated the local region andcaused a global cooling that lasted a year or two. Heeding warnings from geologists, the Philippine government evacuated the region prior to the maineruption, keeping loss of life to a minimum. In contrast,Tambora’s eruption and aftereffects killed 90,000 people. Courtesy of the United States Depart-ment of the Interior, U.S. Geological Survey, and David A. Johnston (Cascades Volcano Observatory).

MayJun13_22 4/11/03 5:26 PM Page 17

Mercury -

meters. Tambora’s dust funnel pumped 200megatons of dust, rock, and aerosols intothe stratosphere. In the immediate after-math, violent winds blew throughout thearea and pumice chunks 20 centimeterslong rained down on the surroundingregion. Floating ash islands formed in thesea and a tsunami ravaged nearby shore-lines. Darkness covered the area for days,with hot and cold air pockets wafting about.

All of this destruction occurred far fromEuropean and American eyes. But

astronomers throughout Europe observeddimmer stars in 1815 — most significantlyfrom September 6 to 20. On these days, andat later times, people in different locationsaround the world saw strikingly beautifulsunsets characterized by red, white, andyellow bands. These spectacular sunsetsresulted from volcanic aerosols and dustthrown into the troposphere and stratos-phere. Similar effects were seen worldwidefrom the 1991 eruption of Mount Pinatuboin the Philippines, but on a smaller scale.

Even though Benjamin Franklin notedthe connection between cool, dim years andvolcanic activity as early as 1784, there hasbeen no documented evidence that scien-tists or the public of 1816 made the samelink between Tambora’s eruption and theirunusual weather. Ironically, the NorthernHemisphere had been experiencing a tem-porary warming temperature excursionprior to the eruption, rising from an earliercooling trend that could have thrown thescientists off track. Sulfate aerosol particles,

Palembang

Ujung Pandang

Tambora(volcano)

Krakatoa(volcano)

Jakarta

Singapaore

Darwin

SINGAPORE

MALAYSIA

BORNEO

SULAWESI(CELEBES)

NEWGUINEA

SUMATRA

JAVASUMBAWA

FLORES

INDONESIA

EAST TIMOR

AUSTRALIA

Tambora appears serene in these images from an airplane (top left) and from the space shuttle (top right), but in 1815 it produced the most powerfulvolcanic eruption of the past 10,000 years.The explosion sheared the volcano nearly in half and ejected an incredible 50 cubic kilometers of material intothe atmosphere.Tambora lies on the island of Sumbawa in Indonesia. Only 26 of the island’s 12,000 inhabitants survived the eruption.Top left imagecourtesy of Rizal Dasoeki,Volcanological Survey of Indonesia.Top right image courtesy of NASA. Map courtesy of Tom Ford.

MayJun13_22 4/11/03 5:27 PM Page 18

- Mercury

made from volcanic gas and dust, blockedsome of the Sun’s heat. Scientists today gen-erally agree that these aerosols were the mainculprit of the “year without a summer.”

The atmospheric ash affected someregions more heavily than others. Thereconstructed regional pressure map for1816 suggests that the volcanic aerosolclouds made the air pressure at sea leveldrop significantly across the NorthAtlantic’s mid-latitudes, pushing mid-latitude cyclone tracks southward. A low-

pressure zone that today sits over Icelandwas displaced southward over England,which brought in wetter weather over West-ern Europe. Weather maps restored by thelate British climatologist Hubert Lamb indi-cate that the average latitude of subpolarIcelandic low-pressure centers in July from1811 to 1820 was about 61° N. In contrast,when sunspots were in higher abundancebetween 1925 and 1934, the low-pressurecenter was displaced some 6° farther north.In cases where the temperature was cold

enough that summer (like in the Northeast-ern United States), snow started to fall inJune and often failed to melt.

A dimmer Sun could have helped spreador move the center for the North Atlanticlow-pressure system sufficiently southwardfrom Iceland to the British Isles to intensifyvolcanic dust and aerosol effects fromTambora. Cool polar air also could havepenetrated farther south toward easternNorth America in the Dalton Minimum.Considering these factors, it’s easy to see

A sunset over Tucson, Arizona after the June 1991 eruption of Mount Pinatubo displays vivid colors and rays. People around the world saw even morepronounced effects following Tambora’s catastrophic April 1815 eruption. Courtesy of William C. Livingston (KPNSO).

MayJun13_22 4/11/03 5:27 PM Page 19

how Tambora’s eruption, combined withweak solar activity, could work together tomake terrible or just weird weather — andunusual sunset colors — in and around1816. Recent research by Tim Ball, MikeChenoweth, Dick Harrington, CynthiaWilson, and other scientists has expandedthe recording of anomalous conditions in1816 to Greenland, Alaska, northeast Brazil,the tropical Atlantic, the eastern Pacific (bythe Galapagos Islands), India, Tibet, SouthAfrica, and elsewhere.

The Wobbling SunWere other factors at work, adding to thereduced solar flux and to the terrible illeffects from Tambora? The Sun’s position inspace moves about the solar system’s centerof mass (barycenter) in cycles that repeatthemselves every 178 to 180 years. Thiswobbling motion is caused by the gravita-tional tug of the planets (mainly Jupiter and

Saturn) and is similar to the stellar motionsthat Geoff Marcy, Paul Butler, MichelMayor, Didier Queloz, Bob Noyes, PeteNisenson, and other astronomers observe todetect extrasolar planets.

Important years pertinent to this articlefor “inertial solar motion” — the barycentershift — are 1632, 1811, and 1990. What’s theconnection, then, between inertial solarmotion and a cold 1816, the eruption ofTambora aside? Inertial motion theory sup-porters state that perhaps it is no accidentthat the timing of the first two years (1632and 1811) corresponds to the two weakestsunspot activity periods ever recorded: 1645-1715 (Maunder Minimum) and 1795-1823(Dalton Minimum). This correlation sug-gests that the 1816 events can be linked tothe Sun’s motion around the barycenter.But just how they are linked — if at all — isanother matter altogether.

In addition, some studies suggest direct

connections (without the Sun’s radiationintervening) between the Sun’s inertialmotion dynamics and phenomena on Earthsuch as earthquakes, volcanic eruptions,massive rainfall, surface air temperatures,and so on. It must be emphasized that froma “hard science” perspective, nobody hasidentified any plausible physical mecha-nisms to support this unproved but intrigu-ing hypothesis.

We must ask more insightful questionsin order to offer explanations for the manyphenomena exhibited by the Sun’s magnet-ic field. One solar inertial motion modelpredicts that a prolonged solar magneticactivity minimum will occur somewherebetween 1990 and 2013. This prolongedminimum is expected to end around 2091.

A Sun-Earth Connection?Given our current state of knowledge, noresponsible scientist would state definitively

Mercury -

2020

1985

19951960

2010

19701990

1975

19652000

2025

2015 20051980

Because of the gravitational pull of theplanets (almost all the result of Jupiter andSaturn), the Sun performs a “dance”around the solar system’s center of gravity.This illustration shows only a small part ofthe dance, which takes 178 to 180 years tocomplete a cycle. Courtesy of Tom Ford.Data courtesy of Geoff Marcy (Universityof California, Berkeley) and Paul Butler(Carnegie Institution of Washington).

MayJun13_22 4/11/03 5:27 PM Page 20

- Mercury

A Sun-Climate Connection? by Douglas Hoyt

he Sun goes through activity cycles that last nearly 11years on average. These cycles are driven by magnetic

fields, which generate sunspots, flares, bright regions knownas faculae, and other disturbances. For these reasons, the Sun’sluminosity changes from year to year. These changes have asubtle but important influence on Earth’s climate.

In the last two decades satellites have shown that when theSun’s magnetic activity is near maximum, the Sun is about0.15% brighter than when activity is near minimum. In addi-tion, satellites may have observed that the Sun was 0.05%brighter at the 1996 solar minimum than it was during the1986 solar minimum.

One might think that an inactive Sun would be brighter,because dark sunspots cover more of the Sun’s surface nearsolar maximum. But faculae are also more common aroundsolar maximum, and when the Sun is active, the overallbrightening from these faculae dominates the darkening ofsunspots. So an active Sun is brighter than an inactive Sun.Astronomers have reasons to believe that other mechanismsacting over longer time scales, such as changes in tempera-ture, also lead to changes in solar luminosity.

If the Sun’s temperature changes, convective motions deepinside the Sun will also vary. Localized changes in solarconvection lead to changes in sunspot decay and structure. Aglobal change in convection will lead to changes in the lengthof the solar cycle or the solar diameter. Astronomers haveobserved sunspot structure and solar cycle length varying inthe same way over the last century, which indicate a peak insolar luminosity in the late 1930s and minima around 1880and 1975. These changes in solar luminosity have closely par-alleled changes in Earth’s temperature, suggesting a physicalcause-effect relationship.

The Sun’s activity undergoes long-term changes in inten-sity. In periods such as 1645-1715 (the Maunder Minimum),many years can pass without a single sunspot being observed.Many of the sunspots that were seen during this period per-sisted for several solar rotations, indicating they decayed veryslowly, implying reduced solar convection and luminosity.The Maunder Minimum coincided with some of Earth’scoolest climates of the past millennium.

The most recent grand minimum was the DaltonMinimum, which occurred around 1790-1820. It was muchshorter than the Maunder Minimum, and astronomersobserved low levels of solar activity nearly every year. The year1810 was the last full calendar year without any sunspotsbeing observed. Solar cycles during the Dalton Minimumlasted about 14 years on average, compared with the modernaverage of 10.7 years. This solar behavior is consistent with areduced solar luminosity and should be accompanied by acooler climate on Earth.

Indeed, as Willie Soon and Steven Yaskell’s article explains,1816 was known as “the year without a summer” in New

England, and cold weather was felt around the globe.Although Tambora’s eruption in 1815 was a major contribu-tor to the cool weather, a number of cool years preceded 1816,which may have been caused by a dimmer Sun.

Astronomers have estimated that the Sun was fainterduring the Maunder Minimum by anywhere from 0 to about0.7%, with a decrease of 0.3% being a popular figure. Thislatter number is thought to be too small to explain climatechanges, so other indirect solar effects such as changes incosmic ray intensity modulated by changes in solar magneticfield strength may have contributed to climate change. Orthere may have been some indirect effect that is yet unknown.

The level of solar activity over the next century is stillbeing debated. Some astronomers think solar activity willcontinue to increase, but others expect another grand mini-mum to appear because the Sun is overdue for one.

DOUGLAS HOYT is a retired solar physicist and climatologistwho has worked for Raytheon, the National Oceanic andAtmospheric Administration, and the National Center for

Atmospheric Research. In 1979 he discussed the correlationbetween variations in sunspot structure and climate. He has

published nearly 100 papers on Earth’s radiation budget, solarirradiance monitoring, cloud cover variations, aerosols, volcanic

eruptions, and many other topics.

T

On March 7, 2003, the Sun’s disk was blemished by a sunspot largeenough to be seen without optical aid. After Tambora’s eruption,people around the world also noticed naked-eye sunspots. Thesame magnetic activity that produces sunspots also producesbright regions known as plages and faculae.The increased luminos-ity from these features more than compensates for sunspotdimming. But the overall influence of changing solar energy outputon Earth’s climate remains uncertain. Courtesy of SOHO/MIDI.

MayJun13_22 4/11/03 5:27 PM Page 21

Mercury -

that solar activity has direct or consistentcontrol over Earth’s climate (see “A Sun-Climate Connection?” page 21). But whenspecific natural phenomena align, as wasthe case in 1816 with the Sun and Tambora,adverse effects can affect Earth’s climate andpopulation in the short term.

The bad weather in 1816 occurred at aperiod in human history when scienceliteracy was on the rise. But like dentistryand surgery at the time, scientific knowl-

edge was still rather primitive and thinlyspread among the populace. Matters likebarycenter shifts and 11-year sunspot cycleswere still unknown. Even BenjaminFranklin’s pithy geophysical observationswere ignored. But according to Percy ByssheShelley, one thing is certain:

The fountains mingle with the riverAnd the rivers with the ocean.The winds of heaven mix forever.

WILLIE SOON is a physicist at the Harvard-Smithsonian Center for Astrophysics and the

Mount Wilson Observatory. He is also asenior scientist at the George C. Marshall

Institute and the senior science contributorto the environmental science page at

www.techcentralstation.com. STEVEN H. YASKELL works for Ericsson

Radio Systems in Sweden and is a writer andnatural historian focusing on aspects in the

history of science. World Scientific PublishingCompany will publish their book manuscript

about the Maunder Minimum in 2003.

Recent Exciting DevelopmentsIn Astronomy And

AstrophysicsJune 30 - July 3, 2003

Professor Paul C. Joss

This course is ideal for anyone who wishes tolearn more about the ongoing explosion ofhuman knowledge in the fields of astronomy,astrophysics and cosmology. It will cover avery broad range of topics, from the origin and evolution of the earth to the birth and structure of the universe as a whole. There will be five lectures each day. At the end of each day’s lectures, there will be a roundtable discussionamong the lecturer and participants. All lecturematerials will be distributed to participants atthe conclusion of the course. This course isintended for interested laypersons, not for professionals in astronomy and astrophysics.

MIT Professional Institute,77 Massachusetts Ave., Rm. 8-201,

Cambridge, MA 02139-4307Phone 617.253.2101; Fax 617.253.8042

professional-institute@mit.edu http://web.mit.edu/professional/

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

MIT

S u m m e r P r o f e s s i o n a l P r o g r a m sS u m m e r P r o f e s s i o n a l P r o g r a m s

MayJun13_22 4/11/03 5:27 PM Page 22