Climate Change & Solar Variability

Evidence the Maunder Minimum Caused the Little Ice Age

Aug 12, 2008

Scientists have evidence that the Little Ice Age resulted from changes in the Sun's energy output associated with long term sunspot and other solar activity cycles.

The exact dates are controversial, but Little Ice Age encompassed the 17th century when global temperatures were below normal.

Sunspots & Solar Activity Cycles

Sunspots are darker cooler regions on the Sun's photosphere, its visible surface. Faculae are hotter and brighter than the rest of the photosphere.There is an 11 year cycle in the amount of sunspots, faculae, and similar solar activity. During sunspot maxima, all types of solar magnetic activity are more common than during sunspot minima.

Satellite measurements show the Sun's total energy output, its luminosity, is a little more during sunspot maximum than sunspot minimum. This difference and the 11 year time period are too small for solar variations during the 11 year sunspot cycle to change Earth's climate.

Longer solar activity cycles can affect Earth's climate. During the Maunder minimum very few sunspots were observed from about 1645 (perhaps as early as 1620) to 1715. Similar minima include:

During extended minima, there are very few sunspots. During grand maxima, the peaks in the 11 year sunspot cycle are higher than normal. The last half of the twentieth century may be another grand maximum.(Hoyt & Schatten 1997, Soon & Yaskell 2003)

The Sun is less luminous during sunspot minima, so during the Maunder and other minima, the Sun should have been less luminous for extended times. The Sun should also have been more luminous during the medieval grand maximum. Solar luminosity variations affect the energy in Earth's climate system.

Temperature Reconstructions

Climatologists have reconstructed global temperatures over the past 1000 years. The Maunder minimum matches the coldest portion of the Little Ice Age. During the medieval grand maximum it was nearly as warm as the late twentieth century.

A cooling trend started in the late 13th century, as the medieval grand maximum ended. Before the coldest portion of the Little Ice Age, it was nearly as cold as the 17th century around 1350, during the Wolf minimum and around 1450, during the Spoerer minimum. The late 1700s were nearly as warm as the average for the past 1000 years, but the first part of the 19th century, during the Dalton minimum, was again quite cold.(Foukal et al. 2006)

Over the last millennium global temperatures have correlated well with the amount of sunspot activity and inferred solar luminosity variations. These correlations are strong evidence, but not proof, that solar variability caused the Little Ice Age and other climate changes in the last millennium.

Current Global Warming

Global warming is usually attributed to manmade causes, such as increased carbon dioxide emissions. Venus shows that carbon dioxide in a planet's atmosphere increases its temperature, so greenhouse gasses are certainly a major source of global warming. However solar variations may also contribute. If so, further curbing carbon emissions to counteract solar effects might be wise.

The problem of global climate change is more complex than usually portrayed in the popular media. Scientists do not yet have all the answers.