Evidence for the Little Ice Age
Climate Researchers Use Proxies to Reconstruct Global Temperatures
Aug 8, 2008
Accurate weather records for the time period of the Little Ice Age do not exist because accurate thermometers and other weather instruments had not been invented. To reconstruct climate conditions during this time period climatologists must use proxies for climatic conditions and anecdotal evidence. This is not ideal, but in all areas of science researchers must often do their best with less than ideal data.
Proxies for Climate Studies
A proxy used for climate studies should be something both that is affected by climate conditions and that scientists can clearly examine and accurately date. Ideally the proxy study should be done at several locations on Earth to separate global from local climate trends.
In a proxy study, climate researchers use existing weather records to study the relation between climate conditions and the proxy for the recent past. A statistical analysis allows the researchers to differentiate between real correlations and spurious effects and to gauge the validity and strength of the correlation.
Having established the correlation between climate conditions and the proxy, researchers can extrapolate back in time to eras without weather records. For the more distant past, these studies become more difficult and less accurate, but past climate conditions have been reconstructed.
Tree ring studies are the most common proxy for climate studies. Trees grow more quickly when there is enough rain and when the temperature conditions are right. Both the temperature and the amount of rainfall can therefore affect the thickness and density of annual tree rings.
Notice that both temperature and rainfall conditions affect the tree rings. Like most proxy studies, having more than one variable affecting the proxy adds complexity. The statistical analysis helps sort this out.
Ice cores are a commonly used proxy in polar regions. Climate conditions can affect the amount of ice that accumulates each year, the amount of ice that melts and refreezes, and ratios of some isotopes. In ocean regions coral growth properties are a commonly used proxy for climate conditions.
Anecdotal Evidence
There is also a considerable amount of anecdotal evidence for the Little Ice Age. Such evidence is usually not considered as valid as accurate data, but an overwhelming amount of anecdotal evidence can be convincing.
Personal diaries and similar records often have weather information. They may note such things as unusually cold winters or unusual freezing of lakes or rivers. These diary notations are seldom quantitative, but can point to unusually cold conditions.
Before photography, painters strove for realism. Paintings of winter landscapes provide evidence for the Little Ice Age, showing more frozen landscapes and bodies of water in places that were ordinarily warmer.
There are enough such paintings, diary entries, and other anecdotes to suggest that the 17th century was much colder than normal, at least in Europe.
The anecdotal evidence and proxy climate reconstructions convinces most climatologists that the Little Ice Age was colder than normal. The Little Ice Age occurred during the time of the Maunder minimum, a period of low sunspot activity, suggesting that solar variability associated with long term solar activity cycles caused the global climate change.
Further Reading
Foukal, P., Fröhlich, C. Spruit, H. and Wigley, T.M.L., "Variations in Solar Luminosity and Their Effect on Earth's Climate" Nature, v. 443, p. 161-166. 2006.
Golub, Leon and Pasachoff, Jay M. Nearest Star The Surprising Science of Our Sun. Harvard, 2001.
Hoyt, Douglas V. and Schatten, Kenneth H. The Role of the Sun in Climate Change. Oxford, 1997.
Soon, Willie Wei-Hock and Yaskell Steven H. The Maunder Minimum and the Variable Sun-Earth Connection. World Scientific. 2003.
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