Earth hasn't been this hot in 125,000 years, but scientists say temps are rising much faster now
Millennia ago, species adapted to rising temperatures over thousands of years — not decades
Climate change is warming the planet, but not since the last interglacial period — almost 125,000 years ago — has it been this hot, according to scientists.
While the planet wouldn't have been inhospitable to humans at that time, temperatures would have been 1 to 2 C above pre-industrial times — and up to 8 C higher in the Arctic.
The difference is that the last time the climate warmed to these levels, it did so over tens of thousands of years, allowing species to adapt. Today, climate change is moving far faster.
"We're talking about a couple of hundred years over which these changes have occurred rather than thousands," said Danielle Fraser, a paleobiologist and director of the Beaty Centre for Species Discovery at the Canadian Museum of Nature in Ottawa.
In its sixth assessment report published earlier this week, the United Nations' Intergovernmental Panel on Climate Change (IPCC) warned that in several scenarios, Earth will surpass 2 C above pre-industrial times within the century unless significant reductions in carbon dioxide and other greenhouse gas emissions occur in the coming decades.
"We've managed to raise global temperatures over a degree in 100-plus years," said climate scientist Jessica Tierney in a conversation with Day 6. "To the best of our knowledge, that's faster than anything that we see in the geological record."
Neither Fraser nor Tierney were involved in the IPCC report.
Adapting quickly
Fraser says that aside from the temperature, one of the most notable differences in Earth's landscape 125,000 years ago would have been roaming mastodons.
"We had a very typical, what I would call Pleistocene fauna ... [including] mammoths and mastodons, but we also had things like giant ground sloths," she told Day 6 guest host Peter Armstrong.
But as temperatures crept higher, so, too, did these massive animals.
While they were once common in what would today be known as Texas and Florida, Fraser explains that mastodons actually moved north to Yukon in order to escape the heat.
This migration, however, took place across a largely empty landscape. It would be far more difficult to do today because much of the land has been developed by humans.
"When you have a city in the way or you have a road in the way, or a huge swath of agricultural land in the way, this creates a big problem for both plants and animals," Fraser said.
The development of urban areas and farmland in Prairie regions has already interrupted the pronghorn antelope's northern and southern migration routes, Fraser said as an example.
"We're presenting them with something that has never occurred before in history, which is one species [humans] that has basically engineered the world to fit their needs," she said.
"So although I think that, yes, both humans and plants and animals are able to adapt, I think they require more time and they require more space."
Melting ice sheets and extreme weather
Tierney cautions that comparing today's climate change to the changes of 125,000 years ago isn't a perfect analogue.
During the interglacial period, the rise in temperatures wasn't caused by carbon emissions in the atmosphere but rather by a shift in the Earth's orbit.
The last time atmospheric CO2 caused temperature rises similar to those occurring today was more than two million years ago, in the Pliocene period, when temperatures were 3 to 4 C higher than normal.
Atmospheric carbon dioxide levels are currently well over 400 parts per million. During the Pliocene, it's believed CO2 levels reached 350 parts per million — which had grave effects on sea levels.
"During the Pliocene, we think that most of the Greenland ice sheet was gone, if not all of it. Most of west Antarctica had melted back," Tierney said.
"This translates to an increase in sea level [that] could have been as high as 20 metres."
Ice sheets, Tierney says, can take thousands of years to melt, so it's not expected that we will see changes this drastic in our lifetime.
It's also believed that monsoon systems were generally stronger during the Pliocene — and current warming projections show a "symmetry" with ancient patterns, she adds.
Optimism for reducing greenhouse emissions
The effects of climate change are already obvious in many parts of the world, with many regions facing record-setting heat waves and wildfire seasons, as well as drought.
The Arctic is warming at more than twice the rate of the rest of the world, according to the IPCC report. The permafrost is thawing, and the length of snowfall during the spring is declining and expected to continue.
Meanwhile, Arctic sea ice cover is at its lowest level since 1850, and the Arctic is projected to be practically ice-free at its summer minimum in roughly 30 years.
At current levels of atmospheric CO2, various reduction scenarios projected by the IPCC paint an alarming picture.
"The [IPCC's] lowest emission scenario has us cutting emissions immediately and eventually going net zero — and in fact, even taking CO2 out of the atmosphere at some point — and that scenario would keep us at 1.5 C global warming by the end of the century," Tierney said.
"We would expect to still see some of the same extreme events that we're seeing today."
Despite the IPCC's warnings, Fraser says she's optimistic that the situation can improve — and keep us away from climate change experienced millennia ago.
The rapid development of COVID-19 vaccines to fend off the pandemic is proof that humans "can do big things and take care of big problems" when needed, she said.
"I'm pretty hopeful that we can come together as a global community and decide that we need to stop pumping as much greenhouse gas into the atmosphere as we can."
Written by Jason Vermes with files from CBC News. Produced by Sameer Chhabra.
Hear full episodes of Day 6 on CBC Listen, our free audio streaming service.
