A new study from Denmark has found that fluctuations in the orbit of the Earth has been causing periods of dramatic, short-term global warming for at least 1.4 billion years. These fluctuations, known as Milankovitch cycles, are even responsible for some long-term global warming of today's climate.
While researchers acknowledge that greenhouse gases are the most dominating force behind the changes to 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," the study's main author and a professor at Nordic Center for Earth Evolution, University of Southern Denmark, Donald Canfield says.
Canfield and his colleagues examined 1.4 billion-year-old marine sediment from northern China. They found evidence of "repeated climate fluctuations, reflected apparent changes in wind patterns and ocean circulation that indicates orbital forcing of climate change." This same force is also the 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," Canfield says. "This research will also help us understand how Milankovitch cyclicity ultimately controls climate change on Earth."
Most scientists say the sun currently plays little to no role in the global warming that has occurred since the mid-1800s and that warming is largely because of carbon dioxide emissions from the use of fossil fuels.
"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.
The Earth has been gradually warming since the end of the last ice age beginning about 11,000 or 12,000 years ago. Since that time sea levels have been rising. But within this gradual warming trend, the climate has also shown much instability.
"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 says. "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."
