Tag Archives: radiocarbon dating


Kurt Refsnider (left) and Gifford Miller (right), U of CO Boulder researchers, hunting for tundra plants exposed on the margin of a retreating ice cap on Baffin Island in Arctic Canada.

In 1783, Benjamin Franklin wrote a paper blaming an extremely cool summer on volcanic dust from the eruption of Iceland’s Laki volcano.  Furthermore, Franklin blamed the huge amounts of erupted sulfur dioxide for the death of much of Iceland’s livestock and for the famine that wiped out a quarter of the island’s human population.

What the statesman was referring to is known as a volcanic winter.  After a large and particularly explosive type of volcanic eruption, volcanic ash and droplets of sulfuric acid obscure the sun and raise Earth’s ability to reflect solar radiation, resulting in a drop in global temperatures for a period of time.

The 1991 explosion of the stratovolcano Mount Pinatubo in the Philippines cooled global temperatures for 2-3 years by half a degree Celsius.

Though there’s considerable debate among climate scientists regarding the Little Ice Age, many are coming to accept the explanation that volcanic eruptions caused the Little Ice Age.  Disagreements continue, though, as to when the period began and what prolonged it.

Researchers from the University of Colorado may have a good start on unraveling the riddles.  Gifford Miller and Kurt Refsnider subjected dead vegetation they’d collected in the Canadian Arctic to radiocarbon dating.  Most of the dates at which the vegetation died from the encroachment of snow and ice clustered at two periods of time:  1275 and 1450 CE.

Miller and his colleagues pointed to a likely cause of the sudden cooling:  a period of at least four major volcanic eruptions starting in 1275 and continuing through the 1800s.

David Schneider, a climate scientist at the National Center for Atmospheric Research in Boulder, CO, expressed a remaining unanswered question in the minds of researchers:  “Volcanism explains the abruptness (of the Little Ice Age), but it can’t account for the longevity (of the age).  This has always been the problem with the volcanic explanation. . . .  Volcanoes can make it cold, but they can’t keep it cold.”

Miller and his team used computer modeling to determine how repeated, short-lived episodes of volcanism could trigger centuries-long cold periods.  Their modeling suggested that the persistent cold summers after the eruptions could be explained by a sea ice-ocean feedback originating in the North Atlantic Ocean.

Prolonged cooling from repeated eruptions would have caused Arctic sea ice to expand to the south until it reached warmer temperatures and melted.  Because sea ice contains almost no salt, when it melted it created a less-dense freshwater cap over the seawater.  The cap acted as an insulator, weakening heat transfer from the tropics to the North Atlantic and, in effect, creating a self-sustaining feedback system that could last long after the effects of the volcanic aerosols subsided, Miller says.

Schneider admits that such a scenario is plausible.  “This study is really the first to explain how a short-lived event like a volcanic eruption can trigger cooling that lasts for centuries.”

However, he still has questions.  “Before the modern era, there are only a few lines of evidence to figure out when and where volcanic eruptions occurred.”  Dating of ash in ice core records suggests an eruption on the island of Vanuatu in 1450.   But records of a 1275 eruption are ambiguous.

from  Wikipedia, “Volcanic Winter”    EARTH, The Science behind the Headlines, May 8, 2012—study published in Geophysical Research Letters    



NOTE:  The dates I’m using regarding the Little Ice Age (LIA) in this series are approximate.  However, all are CE.

Researchers’ conclusions regarding what happened when and where differ.  Only last year was definitive proof available that the Little Ice Age had extended as far south as the Patagonian region of Chile.

Jorge Montt Glacier, Southern Patagonian ice field.

A team of scientists studied tree rings from old trees recently exposed by the retreat of the Patagonian glaciers and radiocarbon dated sample from the trees.   The dating showed the trees had been iced-over between the mid 1500s and mid 1700s as part of the Little Ice Age glaciation.

The Earth is currently in an interglacial period, meaning that the last significant glacier scraped its way down from the North Pole about 14,000 years ago and receded about 10,000 years ago.  In northeastern Ohio, it traveled as far south as the Canton area, where warmer temperatures caused it to melt and begin its retreat.

 The Little Ice Age

At some point during the Middle Ages, glaciers began expanding and creeping southward. Radiocarbon dating of dead plants established glacial advances as early as 1275 CE.

Summers became wet and cold, causing the African Niger River to flood.  Winters brought unprecedented depths of snow, even in Africa and South America.

In Europe and the Americas, torrential rainfall and cooler temperatures destroyed crops.  In 1315, famine spread in Europe, causing horrific deaths, diseases and cannibalism.  Additionally, the sparsity of plants drove animals to forage closer to humans, bringing their plague-infested fleas right into centers of population.  The Black Death spread from Asia to the Middle East to Europe and to Africa, wiping out half of Europe’s population and significant numbers of other populations.

Famine and plagues led to social unrest across the globe, weakening the Mongol hold over China and thus enabling the Chinese to overthrow the Mongol Dynasty.

In Europe, the nobility fought desperately to extinguish the Peasant Revolt.  Though the revolt failed, so many of the peasant class had died from famine and plague that the nobility were forced to work their own land with their own hands, thus weakening the feudal system.

Thames Frost Fair, 1683-84, Thomas Wyke

Londoners, though, found a way to make merry during the winter of 1683-84, a time known as “the great frost.”  The Thames River froze solid and became the occasion for a Frost Fair.  The ice activities, described by John Evelyn included “ . . . sleds, sliding with skeetes, a bull baiting, horse and coach races, puppet plays and interludes, cooks, tippling and other lewd places, so that it seemed to be a bacchanalian triumph, or carnival on the water.”

Evelyn duly noted the downside of “the great frost:”  “The fowls, fish and birds, and all our exotic plants and greens universally perishing.  Many parks of deer were destroyed, and all sorts of fuel so dear that there were great contributions to keep the poor alive.  London, by reason for the excessive coldness of the air hindering the ascent of the smoke, was so filled with fuliginous steam of the sea-coal . . . that one could hardly breath.”

During the time of “the great frost” on North American shores, the ice on Lake Superior didn’t melt until June.  In 1780, New York Harbor froze, letting people walk from Manhattan to Staten Island.

The Caldera of Mt Tambora, island of Sumbawa, Indonesia

In 1815, Mt. Tambora erupted, further cooling the planet.  In 1816, “The Year without a Summer,” Quebec had a foot of snow in June.

Postcard of Thames River, Norwich, CT, frozen in 1906

As this postcard shows, incidents in the early 20th Century bore witness to the lingering effects of the Little Ice Age.

from Wikipedia “Frost Fairs,”       Examiner.com, May 8, 2012       No TricksZone, October 16, 2011—study published in climate of the Past        EARTH, The Science behind the headlines, May 8, 2012—study published in Geophysical Research Letters    

Coming up:  Causes of the prolonged Little Ice Age.