Little Ice Age was due to low solar irradiance

The Sun is the only real source of energy available at the surface of the earth (and any heat from nuclear reactions at the earth’s core is extremely small if not completely negligible). That the oceans have a much higher heat capacity than the atmosphere at the surface of the earth is obvious. It seems also fairly clear to me that it is the dynamics of ocean – atmosphere interactions which control climate and weather. And it is the oceans and long time scales which dominate climate while it is the atmospheric variations and short time scales which determine weather.

But the driver is always the Sun.

A new paper in Nature GeoScience “used seafloor sediments taken from south of Iceland to study changes in the warm surface ocean current. This was done by analysing the chemical composition of fossilised microorganisms that had once lived in the surface of the ocean. These measurements were then used to reconstruct the seawater temperature and the salinity of this key ocean current over the past 1000 years.”

The researchers found that ” low solar irradiance promotes the development of frequent and persistent atmospheric blocking events, in which a quasi-stationary high-pressure system in the eastern North Atlantic modifies the flow of the westerly winds. We conclude that this process could have contributed to the consecutive cold winters documented in Europe during the Little Ice Age.”

Paola Moffa-Sánchez, Andreas Born, Ian R. Hall, David J. R. Thornalley, Stephen Barker. Solar forcing of North Atlantic surface temperature and salinity over the past millenniumNature Geoscience, 2014; DOI: 10.1038/ngeo2094

AbstractThere were several centennial-scale fluctuations in the climate and oceanography of the North Atlantic region over the past 1,000 years, including a period of relative cooling from about AD 1450 to 1850 known as the Little Ice Age. These variations may be linked to changes in solar irradiance, amplified through feedbacks including the Atlantic meridional overturning circulation. Changes in the return limb of the Atlantic meridional overturning circulation are reflected in water properties at the base of the mixed layer south of Iceland. Here we reconstruct thermocline temperature and salinity in this region from AD 818 to 1780 using paired δ18O and Mg/Ca ratio measurements of foraminifer shells from a subdecadally resolved marine sediment core. The reconstructed centennial-scale variations in hydrography correlate with variability in total solar irradiance. We find a similar correlation in a simulation of climate over the past 1,000 years. We infer that the hydrographic changes probably reflect variability in the strength of the subpolar gyre associated with changes in atmospheric circulation. Specifically, in the simulation, low solar irradiance promotes the development of frequent and persistent atmospheric blocking events, in which a quasi-stationary high-pressure system in the eastern North Atlantic modifies the flow of the westerly winds. We conclude that this process could have contributed to the consecutive cold winters documented in Europe during the Little Ice Age.

Cardiff University Press Release:

Changes in the sun’s energy output may have led to marked natural climate change in Europe over the last 1000 years, according to researchers at Cardiff University. The study found that changes in the Sun’s activity can have a considerable impact on the ocean-atmospheric dynamics in the North Atlantic, with potential effects on regional climate.

Scientists studied seafloor sediments to determine how the temperature of the North Atlantic and its localised atmospheric circulation had altered. Warm surface waters flowing across the North Atlantic, an extension of the Gulf Stream, and warm westerly winds are responsible for the relatively mild climate of Europe, especially in winter. Slight changes in the transport of heat associated with these systems can lead to regional climate variability, and the study findings matched historic accounts of climate change, including the notoriously severe winters of the 16th and 18th centuries which pre-date global industrialisation.

The study found that changes in the Sun’s activity can have a considerable impact on the ocean-atmospheric dynamics in the North Atlantic, with potential effects on regional climate.

Predictions suggest a prolonged period of low sun activity over the next few decades ……..

Though their study has nothing whatever to do with global warming and any man-made effects they still feel it necessary to add this caveat (presumably because the reviewers, and the Journal, or both, insisted).

Predictions suggest a prolonged period of low sun activity over the next few decades, but any associated natural temperature changes will be much smaller than those created by human carbon dioxide emissions, say researchers.

Advertisements

Tags: , , ,


%d bloggers like this: