Little Ice Age (LIA)

A brief cold period may have occurred during the seventeenth and eighteenth centuries. Some researchers think that the lower temperatures resulted from a reduced solar energy output related to the Maunder Minimum in sunspot activity. The possibility that climate variations may be induced by solar activity complicates the conventional theory that human activity is causing global warming.

Background

Indirect and indicates that it was colder than normal during the seventeenth century in Europe, and possibly worldwide as well. Without accurate weather records for this time period, the exact dates of the Little are not known. The coldest period was the seventeenth century, but date estimates range from as early as about 1350 or 1400 to as late as 1850. Indeed, some writers use the term “Little Ice Age” to refer only to that coldest period, while others designate the entire period from 1350 to 1850 with the term. The coldest portion of the occurred during the time of the Maunder Minimum, a period of virtually no sunspot activity. If the Sun’s luminosity is slightly lower during periods of reduced sunspot activity, the Little Ice Age may have been caused by a temporary decrease in the Sun’s luminosity.

Little Ice Age

The Little Ice Age was not an ice age. During the various ice ages, which occurred many millennia ago, glaciers invaded temperate mid-latitude regions. The evidence for these ice ages is geologic, because they occurred before recorded history. The Little Ice Age occurred only a few centuries ago. It was colder than normal, but not nearly as cold as the ice ages. Historians know about the Little Ice Age from various anecdotal documents and indirect proxies. There are, however, no accurate weather records for this period, because the instrumentation needed to produce such records had for the most part not yet been invented. Therefore, scientific knowledge of the extent and severity of the Little Ice Age is not precise.

The exact dates of the start and end of the Little Ice Age are somewhat controversial. Authors generally agree that the Little Ice Age encompassed the seventeenth century, but there is some disagreement as to both how long afterward it lasted and how much sooner it started. This disagreement can be understood by examining reconstructed temperatures for the past millennium. The seventeenth century, which was about 0.5° Celsius cooler than the 1961–1990 average temperature, was both the longest-lasting cool period and the coldest period of the past one thousand years. Thus, nearly all researchers agree that this century was part of the Little Ice Age.

The entire period from about 1300 to the late nineteenth century was cooler than normal for the millennium. However, most of this time was not as cold as the seventeenth century, and there were some relatively warm periods during these centuries. The first half of the nineteenth century was colder than normal, but the eighteenth century was about as warm as the average for the millennium. Thus, the Little Ice Age may have lasted as late as 1850, but it may have ended in the early 1700s.

The period from 1000 to shortly after 1200, the Medieval Warm Period, was nearly as warm as the end of the twentieth century. Average temperatures then dropped fairly quickly during the late thirteenth century, making it possible to date the beginning of the Little Ice Age as early as about 1350 to 1400. The middle of the fourteenth and fifteenth centuries were nearly as cold as the seventeenth century, but there were warmer periods about 1400 and during the first portion of the sixteenth century. Thus, the Little Ice Age may not have started until the seventeenth century.

The uncertainty of dating the beginning and end of the Little Ice Age results from the facts that the cool climate from approximately 1350 to 1850 was interspersed with relatively warm periods and that the longest-lasting and coolest period was the seventeenth century. The exact time period of the Little Ice Age is therefore fairly loosely defined.

Evidence for the Little Ice Age

Thermometers were not invented until the end of the sixteenth century, and widespread, systematic use of accurate thermometers did not occur until much later. There are therefore no accurate weather records to verify the Little Ice Age. Climate researchers must use other lines of evidence, including both various and anecdotal evidence.

The most common proxy studies for climate involve tree rings. The thickness and density of the rings vary with various climatic conditions, including temperature and rainfall. In polar regions, studies of various properties of ice cores provide climate information. The properties include the rate at which ice accumulates, layers that have melted, and isotope ratios. Growth thicknesses and other properties of corals can also provide climate information.

For all of these proxy studies, climate researchers statistically analyze the relationship between the proxy and climate conditions during recent periods for which accurate weather records exist. The researchers then extrapolate the climate conditions back to the dates before accurate weather records. The further back researchers extrapolate, the less accurate the proxy is in reconstructing climate conditions. Hence, climate estimates for the first half of the millennium are less accurate than are more recent estimates. Proxy studies are further complicated by the fact that multiple variables can affect the proxy. For example, are affected by both temperature and rainfall conditions.

In addition to proxy studies, there is anecdotal evidence for the Little Ice Age. Examples of this type of evidence include such things as diary entries and paintings. Diary entries might include reports of unusual freezings of various bodies of water, extreme snowfalls, and so forth. Paintings in eras when artists strove for realism can also depict frozen landscapes and bodies of water. If the paintings made during a particular time period show a large number of frozen landscapes of locations that seldom freeze now, researchers can conclude that the time period was cooler than normal. These lines of evidence are not scientific, but many reports of a particular time period being colder than normal strongly suggest that it actually was colder, even in the absence of scientifically reliable weather records. These lines of evidence apply primarily to Europe, so the Little Ice Age could have been either a strictly European phenomenon or a global phenomenon.

The Maunder Minimum and the Little Ice Age

There is fairly strong evidence that variations in the Sun’s luminosity related to sunspot activity caused the Little Ice Age.

Sunspots are dark regions on the surface of the Sun caused by solar magnetic activity. Solar magnetic activity also causes bright areas, or faculae, on the Sun’s surface. The Sun undergoes an eleven-year cycle regulating the number of sunspots, faculae, and related solar magnetic activity it experiences. Satellite measurements over the most recent solar cycles show that the Sun’s luminosity is a very small amount higher during sunspot maximum than during sunspot minimum. The net effect of the bright areas on the Sun is slightly larger than the net effect of the dark areas, so the Sun is brighter during the sunspot maximum.

There are also less well established longer cycles in solar activity. Notably, the Maunder Minimum was a period from about 1645 (possibly as early as 1620) to 1715 when there were very few sunspots. This period corresponds to the coldest portion of the Little Ice Age. If the observation that the Sun emits less energy during periods of minimal sunspot activity holds, then the Sun’s lower luminosity during the Maunder Minimum may have caused the coldest portions of the Little Ice Age.

Closer comparison of the sunspot activity and global temperatures over the past thousand years supports this hypothesis. The warm period from 1000 to 1200 corresponds to the Medieval Grand Maximum in sunspot activity: During sunspot maxima, there were many more sunspots than is usual during sunspot maxima. There were also other extended periods of very few sunspots similar to the Maunder Minimum, including the Spörer, Wolf, and Dalton minima. Like the Maunder Minimum, these other minima correspond to the cooler periods of the extended Little Ice Age. It is not proven that variations in the Sun’s luminosity caused the Little Ice Age, but it seems to be the most likely explanation.

In 2022, researchers at the University of Massachusetts Amherst presented new evidence for the cause of the Little Ice Age. Scientists hypothesized that in the late 1300s, sea temperature increased in ocean waters in Earth’s tropical areas. As this warmer water circulated northward to mix with Arctic water, it caused the rapid melting of Arctic ice. The cooler North Atlantic waters triggered a series of climatic events that soon led to a reduction in global temperatures. This climate change became particularly notable in Europe.

Many of the effects of the Little Ice Age may have fundamentally altered the social and economic interactions of human societies. In a 2019 article, The New Yorkerwriter John Lancaster explores a book by German writer Philipp Blom. Blom hypothesizes this period of intensive cold adversely impacted food production. This led to the sale and distribution of agricultural products becoming centralized, particularly in Europe. In addition to promoting the creation of commercial hubs such as cities, more complex systems of markets and trading developed. The wealth accumulated in these cities began to finance European exploration on other continents, leading to the establishment of colonies.

Context

Global warming, especially since the latter half of the twentieth century, has become a serious worldwide concern. Most climate researchers attribute this global warming to causes, particularly increased emissions of and other greenhouse gases (GHGs). The extremely hot surface temperatures on Venus clearly demonstrate that CO₂ can warm a planet.

If, however, the Little Ice Age resulted from solar luminosity variations related to long-term solar activity cycles, then there is the possibility that similar solar variations are contributing to current global warming. Some, but not all, late-twentieth-century sunspot maxima were higher than normal, suggesting the possibility that Earth is entering another sunspot grand maximum similar to the Medieval Grand Maximum. If this is the case, then global warming may have solar variations as well as increased GHGs as a component cause.

Key Concepts

• luminosity of Sun: the total energy output of the Sun every second, measured in watts
• Maunder Minimum: a period from about 1645 to about 1715 when very few were observed
• sunspot cycle: also known as the solar activity cycle, an eleven-year cycle in the number of sunspots and amount of other solar magnetic activity
• sunspot minimum/maximum: the time when there is the minimum/maximum number of sunspots during the eleven-year sunspot cycle
• sunspots: dark spots on the surface of the Sun caused by solar magnetic activity

Bibliography

Barbuzano, Javier. "The Little Ice Age Wasn't Global, but Current Climate Change Is."EOS, 24 July 2019, eos.org/articles/the-little-ice-age-wasnt-global-but-current-climate-change-is. Accessed 13 Dec. 2024.

Eddy, J. A. “The Maunder Minimum.” Science 192 (1976): 1189–1192.

Foukal, P., C. Fröhlich, H. Spruit, and T. M. L. Wigley. “Variations in Solar Luminosity and Their Effect on Earth’s Climate.” Nature 443 (2006): 161–166.

Golub, Leon, and Jay M. Pasachoff. Nearest Star: The Surprising Science of Our Sun. Cambridge, Mass.: Harvard University Press, 2001.

Hoyt, Douglas V., and Kenneth H. Schatten. The Role of the Sun in Climate Change. New York: Oxford University Press, 1997.

Jones, P. D., T. J. Osborn, and K. R. Briffa. “The Evolution of Climate over the Last Millennium.” Science 292 (2001): 662–667.

Lanchester, John. "How the Little Ice Age Changed History."The New Yorker, 25 Mar. 2019, newyorker.com/magazine/2019/04/01/how-the-little-ice-age-changed-history. Accessed 13 Dec. 2024.

LaPointe, Francois, and Raymond S. Bradley. "Little Ice Age Abruptly Triggered by Intrusion of Atlantic Waters into the Nordic Seas."Science Advances, 15 Dec. 2021, www.science.org/doi/10.1126/sciadv.abi8230. Accessed 13 Dec. 2024.

Marshall, Michael. "Climate Crisis: What Lessons Can We Learn from the Last Great Cooling-Off Period?" The Guardian, 9 May 2022, www.theguardian.com/environment/2022/may/09/climate-crisis-lessons-to-learn-from-the-little-ice-age-cooling. Accessed 13 Dec. 2024.

Maunder, E. Walter. “A Prolonged Sunspot Minimum.” Knowledge 17 (1894): 173–176.

Maunder, E. Walter. “The Prolonged Sunspot Minimum, 1645-1715.” Journal of the British Astronomical Society 32 (1922): 140.

Soon, Willie Wei-Hock, and Steven H. Yaskell. The Maunder Minimum and the Variable Sun-Earth Connection. River Edge, N.J.: World Scientific, 2003.