Lake sediments reveal solar influence on climate over the centennial time scale

The relationship between the sun and the climate is a subject of great contention. Just how much do the variations in the sun affect us, and how has this changed in the past? Scientists at the German Research Centre for Geosciences have found that a sudden cooling and increase in windiness and humidity in Europe several thousand years ago coincided with a reduction in solar activity.

The periods in question are known as Grand Minima, and are one of the more severe decreases in solar activity over the centennial timescale. To assess the climate thousands of years ago, the study looked at laminated sediments from a maar lake, allowing dating of annual changes in the climate in Europe. In the period in question, the research revealed a 200 year period of increased wind and rain in line with decreases in solar activity.

"The change and strengthening of the tropospheric wind systems likely is related to stratospheric processes which in turn are affected by the ultraviolet radiation" explains Achim Brauer, initiator of the study. "This complex chain of processes thus acts as a positive feedback mechanism that could explain why assumingly too small variations in solar activity have caused regional climate changes."

Anthropogenic forcing rather than solar activity has categorically been shown to be the driver of recent increases in global temperatures, but it is important to understand just how the sun is affecting our weather. During the 17th and 18th centuries, there was a similar minimum event, where temperatures dipped causing significant climatic effects across Europe.

Modern climate is impacted not only by the solar changes, but also by the anthropogenic changes caused by greenhouse gasses. It is therefore difficult to compare the past to the present, yet understanding how the sun has affected the planet in the past is important in understanding how it could impact us in the future.