Historian Geoffrey Parker notes that a collection of political and economic upheavals around the globe in the 1600s correlates with swings in the planet’s climate. Reviewing Parker’s book, J.R. McNeill writes:
The various economic and political crises of the 17th century were not isolated events but connected.
The earth’s climate experienced a several-century-long cold spell. This represents a statistical outlier in measured average temperatures during a period of several millennia.
Climatologists are able to accurately reconstruct past temperatures, even for periods of time prior to the invention of the mercury thermometer. A wide spectrum of evidence, from tree-ring sizes to glacial expansions and contractions, documents hot and cold periods over the centuries.
Human records, while not recording numerically the temperature in degrees, yield observations about snowfall, rainfall, crop yields, and the freezing of rivers and lakes.
McNeill continues:
They all had a component of bad weather behind them. The Little Ice Age, which extended from about 1250 to about 1850, reached its nadir in the 17th century. That is explained partly by a spate of volcanic eruptions, the dust veils of which reduced the amount of sunshine reaching the Earth’s surface, and partly by a slump in the sun’s energy output called the Maunder Minimum. Colder weather, often dryer weather, and more frequent extreme weather became common in many if not all parts of the world. No one disputes this much, although there are debates about just how much colder it was, and how global it was.
This ‘Little Ice Age’ came on the heels of its antipode, the ‘Medieval Warm Period’ during the tenth through thirteenth centuries. This ‘warm period’ was also a statistical outlier.
Noteworthy is that these two extremes were non-anthropogenic. They occurred before the mass extraction and consumption of fossil fuels like coal, oil, and gas. They occurred before the large-scale use of chlorofluorocarbons.
Temperatures during the first few decades of the twenty-first century are not as warm as the Medieval Warm Period, nor as cold as the Little Ice Age. While some excursions in temperature have occurred in the late 1900s and early 2000s, they have not endured as long as these historic eras.
Because global temperatures have not long sustained hot or cold temperatures as extreme as the historic outliers periods, it is dubious to claim that current climatic instability is the result of human activity.
To be convincing or persuasive, any assertion that climate in the early twenty-first century is significantly or measurably impacted by manmade factors would need to rely on evidence which shows both that we are now in the midst of a climate swing which features temperatures at or beyond the historic outlier levels, and that such a swing will last as long or longer than the historic outlier periods.
We lack evidence to make plausible the claim that current climate patterns have been observably impacted by human activity.
