From the archives: Volcanic eruptions and sea ice expansion explain the Little Ice Age cold event

By Evan Gowan (originally posted 2nd February 2012)

Langjökull glacier in Iceland. Image sourced from: http://en.wikipedia.org/wiki/File:Islande_Langjokull.jpgLangjökull glacier in Iceland.

The BBC reports on a new paper from Miller et al. (2012), which gives
evidence that the Little Ice Age cooling event may have been triggered
by a series of volcanic eruptions over a period of 50 years. The Little
Ice Age cooling event coincided with a drop in northern hemisphere
temperatures, which resulted in the growth of glaciers due to decreased
melting.

Most northern Hemisphere glaciers reached their maximum position during
the Little Ice Age. A detailed history of glacier advance can be
determined by radiocarbon dating organic material, such
as trees and moss, that were buried when glacial ice advanced. For the
Miller et al. study, the age 147 samples from areas located in northern
Canada and Iceland were used to determine the history of ice advance
during the Little Ice Age. The dated samples clustered between 1275 and
1500 AD, with two distinct peaks at 1275-1300 AD and 1430-1455 AD. Few
of the samples were younger than that, reflecting the sustained position
of the glaciers at their maximum position until they began melting
during the past 100-150 years. There were several samples that had dates
that were older than 1000 years, indicating that the glaciers used in
this study have melted further that their position during the Medieval
Warm Period
. The first main peak and the initiation of the Little Ice Age coincided with four major volcanic eruptions, possibly from volcanoes in tropical regions. The second peak coincides with a major eruption that happened in 1452 AD in Vanuatu.

The aerosols from volcanic eruptions can explain the initiation of the
Little Ice Age, but since these emissions do not last long in the
atmosphere, they cannot explain the long duration of cold climate
conditions. Miller et al. ran a series of climate simulations to try and
reproduce the duration Little Ice Age, investigating the possibility
that it was caused by changes in solar irradiance (the amount of energy
the Earth receives from the Sun), sea ice, and oceanic and atmospheric
circulation. The results of their modelling indicate that the expansion
of sea ice after the volcanic eruptions caused an increase in albedo of
the Earth (the amount solar radiation reflected back into space), and
affected oceanic conditions in the north Atlantic. These effects
sustained the cool climate in the northern hemisphere until the mid
1800s.

One of the most interesting results of this study is that changes in
solar irradiance is not necessary to explain the initation and duration
of the Little Ice Age. The coincidence of the Maunder Minimum
(a period of time between 1645 and 1710 AD when there were few sunspots) during the Little Ice Age has been used as evidence that solar variability may explain the event. Low solar irradience could still explain part of the cold climate conditions, but it is not a necessary condition.

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