An abrupt and dramatic rise in temperature hit Antarctica 19,000 years ago, suggesting that modern-day global warming may not be gradual but fast and furious.
James White, University of Colorado associate professor, was part of a team of researchers who discovered the Antarctic warming spike. He said the 18-degree rise in temperature over a few decades amounts to the most dramatic warming ever documented in the Southern Hemisphere.
The finding "gives us a road map to the way big climate changes occur," said White, a fellow at Colorado University's Institute of Arctic and Alpine Research.
The most important lesson of the research, White said, is that climate change may not simply be a gradual phenomenon, in which a certain amount of greenhouse gases means a proportional rise in global warming.
Instead, humans' relentless combustion of fossil fuels could show little impact. Then, suddenly, temperatures could soar.
In explaining this, White drew an analogy with the way his little brother behaved as a child.
"I used to just pester him and pester him and he wouldn't react," White said. "And then I'd poke him (again), and boom, he'd react.
"That's what we're doing to the climate system, we're teasing it," White said. "When it turns around and snaps at us, we have to be ready to adapt to a large change, rather than a slowly but surely gradual change."
At the same time, the prehistoric warming spike is further evidence that significant climate change, while quite possibly exacerbated by the burning of fossil fuels, is also a phenomenon that happened long before people dominated the planet.
"Dramatic climate changes are natural," White said. "There's no doubt about that."
This summer, White and his colleagues analyzed chemical isotopes in kilometer-deep ice cores drilled over the past two years in an area of coastal West Antarctica known as Siple Dome. White called the findings significant, partly because scientists didn't expect them.
"The magnitude of these changes seem to rival the magnitude of abrupt climate changes that have been documented for the last decade in the Northern Hemisphere," White said. "We had not thought that would be the case."
The Southern Hemisphere, with far more water, is a more uniform environment. Therefore, scientists believed, it should have a more stable climate, less susceptible to major swings and prone instead to changes taking thousands of years.
The 18-degree rise in temperature is so significant, White said, that researchers could speculate it might have been a trigger area for the waning of the last Ice Age.
Scientists believe the end of the most recent ice age dates to 10,000 to 20,000 years ago. Before that, great sheets of ice covered much of Europe and North America.
If New York and Chicago had existed then, their grand buildings would have been crushed to rubble by massive glaciers that, at the time, buried the landscape in ice.
What caused the glacial retreat remains a subject of debate among scientists. White said the Antarctic warming might be linked to a drop in humidity over the ocean surface and an increase in water vapor higher in the atmosphere, boosting the greenhouse effect.
Indeed, the warming appears to be aligned with other temperature increases albeit less dramatic ones found in other Antarctic ice-core samples, as well as pre- historic sea-level increases documented by researchers in Australia.
"There are some of my colleagues who say this was to be expected," White said. "That once we start to really study more and more areas of Antarctica, we're going to find (more evidence of) abrupt climate changes."