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Human-made climate change started twice as long ago as we thought

We’re almost 200 years deep in this.

BEC CREW
25 AUG 2016
 

Widely considered to be the product of intense industrialisation and expansion during the 20th and 21st centuries, human-caused climate change has actually been going on for a whole lot longer.

Scientists have found that temperatures started rising as a result of human activity around the 1830s - an entire century earlier than when we thought the rapid rate of warming first emerged. 

 

"It was an extraordinary finding," says one of the team, Nerilie Abram from the Australian National University. "It was one of those moments where science really surprised us. But the results were clear. The climate warming we are witnessing today started about 180 years ago."

Climate reconstructions of the past 2,000 years have been mainly focused on the Northern Hemisphere, and use records based primarily on land temperature records.

But there’s a whole lot more to Earth than just Northern Hemisphere land, so Abram and her team decided to investigate historic global temperatures more widely, by focussing on the Southern Hemisphere, and seeking temperature records in some more unusual places.

After trawling through evidence of climate variations across the world's oceans and continents over the past 500 years, and reconstructing climate histories preserved in corals, tree rings, and ice cores, the team combined this data with the results of thousands of years of climate model simulations.

"A lot is known about the climate record for the time when we have instrumental records," Abram told Ian Sample at The Guardian. "We wanted to look at whether these records give us the full picture."

They were looking for a 'time of emergence', which describes the moment in history when a signal of climate change emerges from the 'noise' of natural climate variability. In other words, climate on Earth is incredibly varied, but some trends are so strong, they stand apart from the usual ups and downs.

 

Until now, the time of emergence has been pinned to the 1930s, when industrial-era warming led to the emergence of regional climate change in the Arctic. 

Previous research had found that despite the large, natural variability of Arctic climate, a rapid rate of warming in the region resulted in the emergence of human-caused climate change during the 1930s. This has been defined as the moment at which Earth started responding to all our extra carbon emissions.

But Abram’s team’s new assessment found that the response of the Arctic occurred approximately 100 years after a sustained, significant warming around the globe had already begun. 

They found that just as greenhouse gas emissions started to increase, thanks to humans ramping up their industrialisation efforts during the mid-19th century, temperatures in the tropical oceans and in the atmosphere above the Northern Hemisphere began to rise.

In the Southern Hemisphere, temperatures starting rising above the norm about 50 years later, near the turn of the century, the researchers found.

The implication is that even though there were less greenhouse gas emissions in the atmosphere during the 1830s than there were 100 years later, Earth still experienced increasing temperatures, so it shows just how quickly our atmosphere responds to heightened levels of carbon dioxide. 

"The changes in greenhouse gases in the 19th century were small compared with the fairly rapid changes we see now, so seeing the climate respond this way was a surprise," Abrams told The Guardian.

So congrats, humans, we've been stressing out Earth way longer than we even thought. No wonder it wants to take our Olympics away from us

The research has been published in Nature, and you can watch the team's animation of temperature trends for the continents and tropical oceans over the last 500 years below:

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