Available observations stretch back centuries and even several millennia for some parts of the globe. Written records include data about snowfall, rainfall, and temperatures. Other measurements include tree-rings and preserved information in glaciers.
Climatologists have found a segment of time which they call “The Little Ice Age.” Exact beginning and ending points for this era are not precise, because it is a general trend and its endpoints are not marked by specific events.
Published research speaks of a narrow Little Ice Age running from approximately 1500 to 1850, and of a broader Little Ice Age starting around 1300 and terminating around 1850.
The coldest part of this epoch seems to stretch from 1600 to 1700. The change in temperature correlated with instability in precipitation and wind patterns.
Secondary effects included a decline in total farmable land available; glacial expansion obliterating villages in the Alps; crop failures and famines; a decline in the North Atlantic cod fishing business in the 1600s; settlements in Iceland and Greenland becoming isolated; increasing sea ice making North Atlantic navigation difficult and dangerous; and a decline in Native American cultures in the upper Mississippi River region.
Some historians have connected this climate change with the phenomenon known as the “Global Crisis” - a series of political, economic, and military upheavals. The Global Crisis has been a standard concept in historiography for some time; but its hypothesized connection to the Little Ice Age is new.
But what caused this? Historian Geoffrey Parker writes that he was prompted to think about the cause of these climate changes in a different way when he heard
an interview on BBC Radio with John A. Eddy, a solar physicist. Eddy had just published a paper in Science on the “Maunder Minimum” — the period between 1645 and 1705 when virtually no sunspots appeared — and he speculated that the prolonged “sunspot minimum” noted by contemporary astronomers during (ironically) the reign of the “Sun King,” Louis XIV, caused an episode of global cooling that earth scientists had christened the Little Ice Age. Eddy also hinted that the Little Ice Age might have contributed to the General Crisis.
Scientists have generated statistical models which locate the coldest section of the Little Ice Age during the seventeenth century, with the coolest segment being between 1650 and 1700. These years seem to be the coldest in at least a millennium, if not longer.
By contrast, an era known as the “Medieval Warm Period” runs from around 1150 to around 1250. This represents a high point for several centuries before and after.
Reduced sea ice during these years in the North Atlantic allowed Vikings to explore westward from Scandinavia.
These extremes happened before the massive burning of fossil fuels which we associate with the Industrial Revolution. Coal was rarely used. Oil and natural gas were almost unknown. The amount of wood burnt was small, given the total global population at the time. Emissions from the burning of fossil fuels cannot have been the cause of these climatic swings.
Geoffrey Parker writes that he was nudged toward considering solar activity and other non-anthropogenic causes for the Little Ice Age, and in turn nudged to see the Little Ice Age as the cause for the Global Crisis, after he
had combined material from the “natural archive” of the period (climate proxy data such as tree-ring size, harvest dates, and glacier advances) with data from the “human archive” (chronicles, letters, “weather diaries,” art, and archeology).
The Global Crisis is also called the ‘General Crisis’ or the ‘World Crisis’ by various historians.
Irregularities in solar radiation are only one potential cause for climatic instability. Other possible causes are fluctuations in volcanic activity, and changes in sea currents.
Volcanic eruptions throw particulates into the atmosphere, which block solar energy and reduce temperatures. Sea currents do not change the total amount of heat on the planet, but can alter its distribution.
Another historian, Kenneth Pomeranz, concurs with Parker’s analysis, writing that
Unusually cool and otherwise troublesome weather for most of the period 1600-1710 resulted in numerous poor harvests.
Thus it seems reasonable to entertain the notion that non-anthropogenic global climate instability was a contributing factor to events like the Thirty Years’ War (1618 to 1648) and Cromwell’s English Civil War (in the 1640s and 1650s).
The dramatic swings of the Medieval Warm Period and the Little Ice Age almost make it reasonable to ask whether warming trends in the late twentieth and early twenty-first century are also possibly non-anthropogenic.
