A new study out of Denmark found that fluctuations in the Earth’s orbit around the sun, called Milankovitch cycles, have been causing periods of dramatic, short-term global warming for at least 1.4 billion years.
Fluctuations in Earth’s orbit are even behind the long-term warming of today’s climate, conclude researchers.
While they acknowledged that greenhouse gases are the immediate dominating force changing Earth’s climate today, they noted that on a larger scale the way our planet revolves around the sun is the ultimate control knob over the climate.
“This study helps us understand how past climate changes have affected Earth geologically and biologically,” Donald Canfield, the study’s main author and a professor at Nordic Center for Earth Evolution, University of Southern Denmark, said in a statement.
Canfield and his colleagues form the University of Southern Denmark and the China National Petroleum Corporation examined 1.4 billion-year-old marine sediment from northern China. What they found was evidence of “repeated climate fluctuations, reflecting apparent changes in wind patterns and ocean circulation that indicates orbital forcing of climate change.” But more importantly, the same orbital forcing that caused the climate to change 1.4 billion years ago is the underlying force behind global warming today, according to Canfield.
“Earth’s climate history is complex. With this research we can show that cycles like the Milankovich [sic] cycles were at play 1.4 billion years ago – a period, we know only very little about,” said Canfield. “This research will also help us understand how Milankovitch cyclicity ultimately controls climate change on Earth.”
Milankovitch cycles occur every 20,000, 40,000 and 100,000 years. In the last one million years, these cycles have caused an ice age to occur every 100,000 years or so. According to Canfield, the Earth is currently in a period of warming that has lasted for about 11,000 years.
While this study does not call into question the theory that man-made greenhouse gases are responsible for rapid warming in the past century, it does shine a light on the Earth’s long climate history. In particular, the role Earth’s position relative to the sun plays in warming and cooling the planet.
Most scientists, however, say the sun currently plays little to no role in the 0.85 degrees Celsius of global warming that has occurred since the mid-1800s — that warming has been blamed largely on carbon dioxide emissions from fossil fuel use.
“While the ranking of individual years can be affected by chaotic weather patterns, the long-term trends are attributable to drivers of climate change that right now are dominated by human emissions of greenhouse gases,” said Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies.
Earth has been gradually warming since the end of the last ice age about 11,000 or 12,000 years ago — sea levels have been rising since then as well. But within this gradual warming trend, the climate has shown lots of instability.
A recent study from Aarhus University found that the climate has varied over long time periods since the end of the last ice age. The climate has been generally cooler in the last 4,000 years, according to researchers, ocean currents in the North Atlantic have been weaker.
But Aarhus University researchers also found that solar activity — the amount of solar radiation hitting Earth — has a big impact on the climate during cool periods, like the one the planet has been going through for the last four millennia.
“We know that the Sun is very important for our climate, but the impact is not clear,” Professor Marit-Solveig Seidenkrantz of Aarhus University said in a statement.
“Climate change appears to be either strengthened or weakened by solar activity,” Seidenkrantz said. “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.”
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