New research suggests the impact of the sun on climate is greater when the Earth is cooler.

Scientists have speculated as to whether or not variations in the sun have triggered climate change in the past, but mounting evidence has suggested that solar activity has a significant impact on how the climate varies over time, Aarhus University reported.

Over the past 4,000 years the researchers believe there has been a close correlation between solar activity and sea surface temperatures in the North Atlantic. During this period the Earth has generally seen cooler climates and weaker ocean temperatures in this region.

"We know that the Sun is very important for our climate, but the impact is not clear," said Professor Marit-Solveig Seidenkrantz of Aarhus University, who is one of the Danish researchers in the international team behind the study. "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." 

To make their findings the researchers looked at summer sea surface temperatures in the northern part of the Atlantic over the past 9,300 years. They measured these temperatures by analyzing marine algae found in sediments on the North Atlantic sea bed. This allowed them to draw comparisons with historical fluctuations of solar energy bursts and ocean surface temperatures. The results showed a link between climate change in the North Atlantic region and variations in solar activity over the past 4,000 years.

"Our climate is enormously complex. By gathering knowledge piece by piece about the way the individual elements work together and influence each other to either strengthen an effect or mitigate or compensate for an impact, we can gradually get an overall picture of the mechanisms. This is also important for understanding how human-induced climate change can affect and be affected in this interaction," Seidenkrantz concluded.

The findings were published in a recent edition of the journal Geology.