The Earth’s climate hasn’t changed simultaneously in both the Northern and Southern Hemispheres since the last Ice Age, until now that is, said a study published in Climate Research.
“What is happening today is unique from a historical geological perspective,” said Svante Björck, a researcher at Lund University in Sweden in a press release.
Serious cataclysms are necessary to change the Earth’s climate in a short time Björck said. And humans seem to be one of them.
“This could be, for example, at the time of a meteorite crash, when an asteroid hits the Earth or after a violent volcanic eruption when ash is spread across the globe. In these cases we can see similar effects around the world simultaneously,” said Björck.
“As long as we don’t find any evidence for earlier climate changes leading to similar simultaneous effects on a global scale, we must see today’s global warming as an exception caused by human influence on the Earth’s carbon cycle,” said Björck.
Björck studied climate archives, such as sediment core samples from oceans, lakes and glacier ice. He examined these for changes in temperature, precipitation and concentration of atmospheric gases and particles.
He found that when temperatures went up in one hemisphere, they either went down or stayed the same in the other.
“My study shows that, apart from the larger-scale developments, such as the general change into warm periods and ice ages, climate change has previously only produced similar effects on local or regional level,” said Björck.
The Little Ice Age, for example, chilled the northern hemisphere causing farm failures, transportation difficulties and economic problems from about 1600 to 1900. The southern hemisphere however doesn’t seem to have been affected.
“This is a good example of how geological knowledge can be used to understand our world. It offers perspectives on how the Earth functions without our direct influence and thus how and to what extent human activity affects the system,” said Björck.
”A Scene on the Ice” (c. 1625) by Hendrick Avercamp painted during the Little Ice Age. (Wikimedia Commons)
A comparison of 10 different reconstructions of mean temperature changes during the last 2000 years. More recent reconstructions are in redder colors, older are in bluer colors. An instrumental history of temperature is also shown in black. (Wikimedia Commons)
The main figure shows eight records of local temperature variability on multi-centennial scales throughout the course of the Holocene, and an average of these [thick dark line]. (Wikimedia Commons)