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Does solar activity affect regional climate?

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A composite image assembled from NASA satellite images shows the UK covered with snow during a spell of cold winter weather in January 2010.

Yes, but effects are small compared to changes driven by greenhouse gases

By Summit Voice

FRISCO — After carefully studying cycles of solar activities and matching them against seafloor sediments that offer clues about ocean temperatures, Cardiff University scientists say low sunspot activity may be linked with phases of cold weather in Europe.

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.

While the effects of variations in solar energy are small compared to the impacts of increasing greenhouse gas concentrations, the effects of solar output on the ocean and atmosphere should be taken into account when making future climate projections, the researchers said.

The findings of study, done in collaboration with scientists at the University of Bern, was published today in the journal Nature Geoscience.

“We used seafloor sediments taken from south of Iceland to study changes in the warm surface ocean current,” said Dr Paola Moffa-Sanchez, lead author from Cardiff University School of Earth and Ocean Sciences.

Analyzing the chemical composition of fossilized microorganisms that had once lived in the surface of the ocean enabled the scientists to reconstruct a record of ocean temperatures and salinity in the region, Moffa-Sanchez explained.

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.

The study findings matched historic accounts of climate change, including the notoriously severe winters of the 16th and 18th centuries which pre-date global industrialization and the buildup of heat-trapping greenhouse gases.

The study showed significant temperature and salinity changes in the north-flowing warm current on time-scales of several decades to centuries. Cold ocean conditions were found to match periods of low solar energy output, corresponding to intervals of low sunspot activity observed on the surface of the sun.

Using a physics-based climate model, the authors were able to test the response of the ocean to changes in the solar output and found similar results to the data.

“By using the climate model it was also possible to explore how the changes in solar output affected the surface circulation of the Atlantic Ocean,” said Prof Ian Hall, a co-author of the study.

“The circulation of the surface of the Atlantic Ocean is typically tightly linked to changes in the wind patterns. Analysis of the atmosphere component in the climate model revealed that, during periods of solar minima, there was a high-pressure system located west of the British Isles,” Hall said.

“This feature is often referred to as atmospheric blocking, and it is called this because it blocks the warm westerly winds diverting them and allowing cold Arctic air to flow south bringing harsh winters to Europe, such as those recently experienced in 2010 and 2013.”

Meteorological studies have previously found similar effects of solar variability on the strength and duration of atmospheric winter blockings over the last 50 years, and although the exact nature of this relationship is not yet clear, it is thought to be due to complex processes happening in the upper layers of the atmosphere known as the stratosphere.

“In this study we show that this relationship is also at play on longer time-scales and the large ocean changes, recorded in the microfossils, may have helped sustain this atmospheric pattern,” Moffa-Sanchez said.

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