The research provides a further piece of the jigsaw as to how Earth’s climate functions and may have implications for climate modelling.
Solar activity is one of the variables in the complex interaction that goes to make up our planet’s climate. Scientists have long debated whether changes in the strength of the Sun have been a factor when Earth has undergone climate change in the past. As more studies are conducted, results point to solar activity and with it the amount of radiation coming from the Sun, affecting how the climate varies over time.
In this latest study, researchers from a group of institutions led by Aarhus University in Denmark, show that, during the last four millenia, a close correlation appears to exist between solar activity and the sea surface temperature in summer in the North Atlantic, a correlation not seen in the preceding period.
The last Ice Age ended roughly 12,000 years ago. Since then, Earth has, over that period, generally experienced a warm climate. But within those 120 centuries, Earth’s climate hasn’t been stable. From time to time, and for long periods, temperatures have varied. Over the last 4,000 years, say the Danish researchers, the planet has experienced a slightly cooler climate. At the same time, North Atlantic ocean currents have been weaker.
Professor Marit-Solveig Seidenkrantz of Aarhus University, one of the Danish researchers in the international team summarized, “We know that the Sun is very important for our climate, but the impact is not clear. Climate change appears to be either strengthened or weakened by solar activity. The extent of the Sun’s influence over time is thus not constant, but we can now conclude that the climate system is more receptive to the impact of the Sun during cold periods – at least in the North Atlantic region.”
A piece of the climate puzzle
Scientists examined summer sea surface temperatures in the northern portion of the North Atlantic over the preceding 9,300 years. Since such historical temperatures, recorded by ships, only cover the last 140 years, to give a complete long-term picture researchers examined studies of marine algae.
These marine algae, known as diatoms, are found in sediments deposited on the North Atlantic sea bed. Their peculiar structure, consisting of transparent cell walls made of silicon dioxide hydrated with a small amount of water — silica. Since silica is the main component of glass, diatoms have sometimes been dubbed “algae in glass houses”.
By analysing algae found in sediments, from the species distribution of these organisms, fluctuations in sea temperature can be reconstructed much further back than the century-and-a-half or so of ship’s records.
From detailed study of these reconstructed records, it’s possible to draw comparisons with records of fluctuations of solar energy bursts over the same timescale. Such a comparison shows a clear correlation between climate change in the North Atlantic and variations in solar activity during the last 4,000 years. Not only that but as well as fluctuations on a scale of hundreds of years, it’s also possible for researchers to zoom in on fluctuations over much shorter periods of 10 to 20 years.
According to Professor Seidenkrantz, this new knowledge provides a small but important piece of the climate jig-saw and should help scientists better understand the workings of the entire climate system.
Professor Seidenkrantz highlighted the complexity of Earth’s climate but suggested that by gathering knowhow, bit-by-bit, of how different factors affecting the planet’s climate system meshed together, gradually a picture could be constructed of how these different inputs influenced each other and lessened or magnified differing climatic changes.
Professor Seidenkrantz added, “This is also important for understanding how human-induced climate change can affect and be affected in this interaction.”
Details of the new research were recently published online in the journal Geology.
