March 11, 2014
North Atlantic Climate Variability Influenced By Solar Activity
redOrbit Staff & Wire Reports - Your Universe Online
A 1,000-year period of pronounced climate variability occurring in Europe could have been the result of changes in the sun’s energy output, according to research published in Sunday’s edition of the journal Nature Geoscience.
In the study, lead author Dr. Paola Moffa-Sanchez of the Cardiff University School of Earth and Ocean Sciences and her colleagues studied seafloor sediments to uncover changes to the temperature and atmospheric circulation in the North Atlantic region.
The warm surface waters that flow across the North Atlantic and warm westerly winds play a key part in the relatively mild climate in Europe – particularly during the winter months. Minor alterations in the transport of heat associated with those systems can result in localized climate variability, and the study’s findings match with historical accounts of climate change (most notably, the severe pre-global industrialization winters of the 1500s and 1700s.)
Dr. Moffa-Sanchez and other scientists from Cardiff University and the University of Bern discovered that changes in the ocean-atmospheric dynamics in the North Atlantic could be heavily impacted by the sun’s activity. In turn, the relationship between sun activity and ocean-atmospheric dynamics could influence the region’s climate.
While some predictions suggest that there will be an extended period of low solar activity over the next several decades, the study authors suggest that natural temperature changes that occur as a result could be far smaller than those resulting from human-caused carbon dioxide and greenhouse gas emissions.
“We used seafloor sediments taken from south of Iceland to study changes in the warm surface ocean current,” Dr. Moffa-Sanchez said in a statement. “This was done by analyzing the chemical composition of fossilized 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.”
In their analysis, the investigators uncovered large, sudden temperature and salinity changes in the north-flowing warm current, dating back at least several decades. They found a correlation between periods of low solar energy output and colder ocean conditions, corresponding to observations of reduced sunspot activity on the sun’s surface.
By using a physics-based climate model, the study authors were able to test how the ocean would respond to solar output changes. The results were similar to the existing data. By using these climate simulations, they said that they were able to explore how solar output changes affected the Atlantic Ocean’s surface circulation.
“The circulation of the surface of the Atlantic Ocean is typically tightly linked to changes in the wind patterns,” said study co-author and Cardiff University professor Ian Hall. “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.”
“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,” he added.
Previous meteorological research had discovered a similar association between solar variability and both the intensity and duration of atmospheric winter blockings throughout the past five decades. The exact nature of this link remains unknown, but the investigators believe that complex processes taking place in the stratosphere (the upper layer of the Earth’s atmosphere) has something to do with the phenomenon.
“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,” said Dr. Moffa-Sanchez.
“Indeed we propose that this combined ocean-atmospheric response to solar output minima may help explain the notoriously severe winters experienced across Europe between the 16th and 18th centuries, so vividly depicted in many paintings, including those of the famous London Frost Fairs on the River Thames, but also leading to extensive crop failures and famine as corroborated in the record of wheat prices during these periods,” she added.
Even though the climate changes anticipated to result from the sun’s activity in the future will be far smaller than global warming resulting from man-made CO2 emissions, the study suggests that regional weather changes associated with the impact of solar output on both the ocean waters and the planet’s atmosphere will have to be accounted for by scientists as they prepare future climate-related projections.