Ice cores from the West Antarctic Ice Sheet. Scientists use these ice cores to measure the presence of carbon dioxide and other atmospheric gases during the last ice age.
by Sarah Kramer
Nov 24, 2014
Yes, humans are releasing huge amounts of carbon dioxide into the atmosphere by burning fossil fuels. But we might be boosting the emissions from an unexpected place: the earth beneath our feet.
Antarctic warming periods in the ancient past shows that soils may have amplified rises in temperature that occurred thousands of years ago. This could mean an unexpected wallop of excess CO2 into the atmosphere in response to global warming and decades of human fossil-fuel.
“Humans are causing climate change,” said Dr. Jeffrey Severinghaus, “But Mother Nature’s going to give it a little kick.”
Severinghaus, a professor at University of California-San Diego’s Scripps Institute of Oceanography, presented this research at the Comer Abrupt Climate Change Conference this fall.
Climate scientists previously thought that atmospheric carbon dioxide rose gradually and steadily when natural sources like soil were involved. However, Severinghaus’ work with ice cores that trap ancient pockets of carbon dioxide show that the rising levels also occurs in abrupt jumps, suggesting that the Earth’s feedback might be magnifying other increases. About half of the carbon dioxide in the atmosphere after the last ice age was distributed in these jumps, he said.
A scientist pulls out one of the West Antarctic ice cores. “Ice has a thermal memory,” said Severinghaus, “the same way a cool cellar has a memory of winter.”
The mismatch at times between the increase in temperature and the increase in carbon dioxide, Severinghaus said, is evidence of a “feedback loop” in the Earth’s natural carbon dioxide releases. He estimated that half of the rise in carbon dioxide levels during the natural warming period that began 18,000 years ago happened in “little jumps,” independent of air-temperature rise.
“We think that these little jumps are telling us that soils do actually give off CO2 in a warming climate,” Severinghaus said. “We want to know if natural soils will give out excess CO2 in response to the warming caused by humans.”
Comparing the Antarctic work to previous investigations on Greenland, Severinghaus and his team found that temperatures rose in the North Atlantic first, with the southern hemisphere warming starting nearly 200 years later. These increases in temperature are also linked to large releases of icebergs into the Atlantic, called Heinrich events.
“What’s really fascinating,” Severinghaus said, “Is that these events happen a long time before the warming.”
Heinrich events are part of a pattern of a shifting global climate reaching back to the last ice age. Once icebergs are released en masse into the North Atlantic, the northern hemisphere cools and the southern hemisphere warms.
The precise timing of Heinrich events wasn’t known until an innovative research technique used by Severinghaus’ team. By melting ice cores and measuring the methane released, scientists could measure changes in atmosphere with unprecedented accuracy.
Blue ice on the West Antarctic Ice Sheet. Blue ice is formed when snowfall compresses to become part of the glacier.
Since methane is well mixed throughout the atmosphere, Severinghaus told fellow scientists, a record of a shift in the Antarctic means a shift worldwide. Carbon dioxide increases more slowly than methane and the air temperature.
Together with increased rain in the tropics and other events, Severinghaus said this shows that the Earth’s climate patterns can shift between states of cooling and warming but remain within a fairly narrow, stable range. The worry is that humans might be pushing these modes to the extreme, potentially launching the Earth into a new range of climate events.
“It’s possible that in this very complicated climate system there might be states that we accidentally discover,” Severinghaus said, “And that, all of a sudden, the climate might change dramatically in a few years.”
Despite the catastrophic messages ancient climates seem to be sending us, Severinghaus said that few people alive now will be around to see the all results of the carbon-dioxide feedback loop or disappearing glaciers. But we can expect to see coastal flooding, more severe storms and droughts—exacerbating starvation, resource conflicts and the problem of climate refugees as populations flee affected areas.
For the Midwest, alternation between extreme drought and heavier rainfall will lead to flooding, endangering crops and livelihoods throughout the region, according to the recently released 2014 National Climate Assessment.
We don’t know, Severinghaus said, “where the natural system will take control and the whole system will shift without us being able to know anything about it.”
Severinghaus emphasized that while the Earth can swing between climate states and even contribute to its own warming, the human element is at the heart of the current abrupt climate change.
“The most important part is that humans are putting [carbon dioxide] into the atmosphere,” he said, “And that’s causing global temperatures to rise.”
