Climate Changes Affect Greenland First, Antarctica in 200 Years
No, I'm not talking about 200 years from present day. But new research has shown evidence of a 200-year lag between climate events in Greenland and Antarctica during the last ice age, and it could possibly help shed light on the consequences of climate change in the future.
The study, published in the journal Nature, also is giving scientists a clearer picture of the link between climate in the northern and southern hemispheres, and how the ocean likely plays a part.
During the last ice age, Greenland experienced abrupt changes in mean annual temperature, each which occurred within several decades. These so-called "Dansgaard-Oeschger events" took place every few thousand years. Meanwhile, Antarctica's climate at the time looked very different. In fact, it was the exact opposite, with the White Continent cooling when Greenland was warm, and vice versa.
In the study, a team of researchers from Oregon State University (OSU) discovered that the abrupt climate changes show up first in Greenland, with the response to the Antarctic climate delayed by about 200 years. The researchers documented 18 abrupt climate events in all during the past 68,000 years.
"The fact that temperature changes are opposite at the two poles suggests that there is a redistribution of heat going on between the hemispheres," lead author Christo Buizert said in a statement. "We still don't know what caused these past shifts, but understanding their timing gives us important clues about the underlying mechanisms.
"The 200-year lag that we observe certainly hints at an oceanic mechanism," Buizert added. "If the climatic changes were propagated by the atmosphere, the Antarctic response would have occurred in a matter of years or decades, not two centuries. The ocean is large and sluggish, thus the 200-year time lag is a pretty clear fingerprint of the ocean's involvement." (Scroll to read on...)
It is no secret that current climate change is also impacting both of these regions today. For instance, Greenland's ice is vanishing faster than previously thought, which could trigger future ice loss and raise sea levels up to a staggering 20 feet. Antarctica is not faring much better, with warming temperatures causing massive ice loss - so much so that it is literally moving the Earth.
However, the researchers behind this latest study note that past episodes of climate change differ from what is happening today. The abrupt events of the ice age were regional in scope - and likely tied to large-scale changes in ocean circulation. Warming today is global and could be primarily driven by human carbon dioxide emissions. Even so, by better understanding the factors that are involved in past climate changes scientists may be able to apply their knowledge to the future.
The discovery of the 200-year climate lag between the two regions came from a new ice core unearthed in West Antarctica, drilled to a depth of 3,405 meters in 2011 and spanning the last 68,000 years, according to researchers. What's more, the ice core analysis gives scientists one of the most detailed records of Antarctica's temperatures. On the other hand, the team already knew a great deal about Greenland temperatures, thanks to more available ice core data.
"Past ice core studies did not reveal the temperature changes as clearly as this remarkable core," noted co-author Eric Steig, whose laboratory may a key measurement of past Antarctic temperatures.
"Previous work was not precise enough to determine the relative timing of abrupt climate change in Antarctica and Greenland, and so it was unclear which happened first," he added. "Our new results show unambiguously that the Antarctic changes happen after the rapid temperature changes in Greenland. It is a major advance to know that the Earth behaves in this particular way."
That's because the area where the ice core was drilled gets lots of annual snowfall, and so it offered scientists a rare, comprehensive glimpse into Antarctica's climate past. This way, the core revealed the relative timing of Greenland and Antarctic temperatures down to several decades.
"We needed a climate record from the Southern Hemisphere that extended at least 60,000 years into the past and was able to resolve fast changes in climate," said Kendrick Taylor, chief scientist on the project. "We considered sites all over Antarctica before selecting the site with the best combination of thick ice, simple ice flow and the right amount of annual snowfall." (Scroll to read on...)
"This will provide a generation of climate researchers a way to test and improve our understanding of how and why global climate changes," Kendrick added.
Based on their findings, researchers say it's "very likely" that the Atlantic Meridional Overturning Circulation, or AMOC, is involved in these abrupt climate reversals.
"This ocean circulation brings warm surface waters from the tropics to the North Atlantic," said Buizert, who is in OSU's College of Earth, Ocean, and Atmospheric Sciences. "As these water masses cool, they sink to the bottom off the ocean. This happens right off the coast of Greenland, and therefore Greenland is located in a sweet spot where the climate is very sensitive to changes in the AMOC."
Though the AMOC seems to play a crucial role in abrupt climate changes, it probably is part of a combination of factors.
"Although ocean circulation may be the key, there are probably other feedbacks involved, such as the rise and fall of sea ice and changes in ice and snow cover on land," Brook said. "There is probably some kind of threshold in the system - say, in the salinity of the surface ocean - that triggers temperature reversals.
"It's not a problem to find potential mechanisms; it's just a question of figuring out which one is right. And the precise timing of these events, like we describe in this study, is an important part of the puzzle."
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