Little Ice Age could well have resulted from reduced solar activity

This paper is particularly interesting because the senior author, Thomas Stocker, is the Vice-Chair of the IPCC and presented the summary of AR5 at the Press Conference last week!!

It is very strange then that the IPCC is so nonchalant about solar effects. In any event whatever the various climate models say, the Landscheidt Minimum is here and global cooling will continue for the next two decades or so. As The Register puts it.

” There’s been criticism for the Intergovernmental Panel on Climate Change (IPCC) over its latest AR5 report from many quarters for many reasons. But today there’s new research focusing on one particular aspect of that criticism.The particular part of the IPCC’s science in question is its accounting for the effects of changes in the Sun on the climate of planet Earth. Many climatologists have long sought to suggest that the effects of solar variability are minor, certainly when compared to those of human-driven CO2 emissions. Others, however, while admitting that the Sun changes only a very little over human timescales, think that it might be an important factor. This matters because solar physicists think that the Sun is about to enter a “grand minimum”, a prolonged period of low activity. 

The current 11-year peak in solar action is the weakest seen for a long time, and it may presage a lengthy quiet period. Previously, historical records suggest that such periods have been accompanied by chilly conditions on Earth – perhaps to the point where a coming minimum might counteract or even render irrelevant humanity’s carbon emissions. The “Little Ice Age” seen from the 15th to the 19th centuries is often mentioned in this context.

Lehner, Flavio, Andreas Born, Christoph C. Raible, Thomas F. Stocker, 2013: Amplified Inception of European Little Ice Age by Sea Ice–Ocean–Atmosphere Feedbacks.  J. Climate, 26, 7586–7602.

doi: http://dx.doi.org/10.1175/JCLI-D-12-00690.1

The University of Berne press release writes:

The study that was realized at the OCCR shows that volcanic eruptions and reduced solar radiation caused global cooling between the thirteenth and the fifteenth centuries. The resulting accelerated formation of sea ice in the Northern Seas triggered a positive feedback process that shaped the Little Ice Age. The winter weather in Europe is largely governed by the so-called North Atlantic Oscillation (NAO). ……. Until now, the NAO was believed to be jointly responsible for the cooling in the early fifteenth century along with volcanic eruptions and weakened solar radiation. The subsequent Little Ice Age continued into the nineteenth century. Now, however, Bernese climate researchers Flavio Lehner, Andreas Born, Christoph Raible and Thomas Stocker reveal that the Little Ice Age was also able to take its course without the influence of the NAO, driven purely by the consequences of strong and frequent volcanic eruptions at the time, a reduced solar radiation, or both together.

Using simulations on the CSCS supercomputer “Monte Rosa”, the climate researchers searched for a feedback process that was capable of triggering the Little Ice Age.

….. For the scientists, the fact that all the slightly altered, realistic simulations and the synthetic ice simulation yielded consistent results is solid proof that the Little Ice Age was primarily governed by external triggers. Volcanic activity and less solar radiation initially caused an increase in sea-ice formation independently of atmospheric circulation. Due to the cooling, the mean sea level pressure gradually increased over the Barents Sea, which enabled the cold air to reach Europe. “However, this pressure response is clearly a delayed reaction of the atmosphere to the preceding processes in the ocean,” says Raible.

Abstract: The inception of the Little Ice Age (~1400–1700 AD) is believed to have been driven by an interplay of external forcing and climate system internal variability. While the hemispheric signal seems to have been dominated by solar irradiance and volcanic eruptions, the understanding of mechanisms shaping the climate on a continental scale is less robust. In an ensemble of transient model simulations and a new type of sensitivity experiments with artificial sea ice growth, the authors identify a sea ice–ocean–atmosphere feedback mechanism that amplifies the Little Ice Age cooling in the North Atlantic–European region and produces the temperature pattern suggested by paleoclimatic reconstructions. Initiated by increasing negative forcing, the Arctic sea ice substantially expands at the beginning of the Little Ice Age. The excess of sea ice is exported to the subpolar North Atlantic, where it melts, thereby weakening convection of the ocean. Consequently, northward ocean heat transport is reduced, reinforcing the expansion of the sea ice and the cooling of the Northern Hemisphere. In the Nordic Seas, sea surface height anomalies cause the oceanic recirculation to strengthen at the expense of the warm Barents Sea inflow, thereby further reinforcing sea ice growth. The absent ocean–atmosphere heat flux in the Barents Sea results in an amplified cooling over Northern Europe. The positive nature of this feedback mechanism enables sea ice to remain in an expanded state for decades up to a century, favoring sustained cold periods over Europe such as the Little Ice Age. Support for the feedback mechanism comes from recent proxy reconstructions around the Nordic Seas

Tags: Arctic, Little Ice Age, North Atlantic Oscillation, Northern Hemisphere, solar effects, sunspots