Long-term climate records are a key to understanding how Earth’s climate changed in the past and how it may change in the future. Direct measurements of light energy emitted by the sun, taken by satellites and other modern scientific techniques, suggest variations in the sun’s activity influence Earth’s long-term climate. However, there were no measured climate records of this type until the relatively recent scientific past.
So, to shorten the story significantly, a couple of science teams cross-checked between two ancient data sources–one, Nile river records from ancient Egypt; and two, ancient European and Asian records of aurorae. The Nile records show patterns of flooding, which indicate climate change. The aurorae records show patterns of solar activity, since the lights are caused by the solar wind slamming into earth’s atmosphere. And the records reveal a thing or two about climate change:
The researchers found some clear links between the sun’s activity and climate variations. The Nile water levels and aurora records had two somewhat regularly occurring variations in common – one with a period of about 88 years and the second with a period of about 200 years.
The researchers said the findings have climate implications that extend far beyond the Nile River basin.
“Our results characterize not just a small region of the upper Nile, but a much more extended part of Africa,” said Ruzmaikin. “The Nile River provides drainage for approximately 10 percent of the African continent. Its two main sources – Lake Tana in Ethiopia and Lake Victoria in Tanzania, Uganda and Kenya – are in equatorial Africa. Since Africa’s climate is interrelated to climate variability in the Indian and Atlantic Oceans, these findings help us better understand climate change on a global basis.”
So what causes these cyclical links between solar variability and the Nile? The authors suggest that variations in the sun’s ultraviolet energy cause adjustments in a climate pattern called the Northern Annular Mode, which affects climate in the atmosphere of the Northern Hemisphere during the winter. At sea level, this mode becomes the North Atlantic Oscillation, a large-scale seesaw in atmospheric mass that affects how air circulates over the Atlantic Ocean. During periods of high solar activity, the North Atlantic Oscillation’s influence extends to the Indian Ocean. These adjustments may affect the distribution of air temperatures, which subsequently influence air circulation and rainfall at the Nile River’s sources in eastern equatorial Africa. When solar activity is high, conditions are drier, and when it is low, conditions are wetter.
The one phrase that never made its way into this story: “carbon footprint.” Because Ramses II didn’t have much of one, and even if his carbon footprint was bigger than the Goracle’s it wouldn’t have done diddly to the Sun’s output.