As the last ice age was ending, about 13,000 years ago, a final blast of cold hit Europe, and for a thousand years or more, it felt like the ice age had returned. But oddly, despite bitter cold winters in the north, Antarctica was heating up. For the two decades since ice core records revealed simultaneous warming and cooling at opposite ends of the planet during this time period, scientists have looked for an explanation.
Results of a new study published this week in the journal Naturebring them a step closer by establishing that New Zealand was also warming. "New advances in the use of cosmogenic isotopes [used in this research] allow dating with hundreds of years' resolution, and correlation of key deposits such as the moraines in New Zealand," said Enriqueta Barrera, program director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the research. "Further application of this technique will reveal the details of climate change in different regions since the last glaciations."
The finding indicates that the deep freeze up north, called the Younger Dryas for the white flower that grows near glaciers, bypassed much of the southern hemisphere. "Glaciers in New Zealand receded dramatically at this time, suggesting that much of the southern hemisphere was warming with Antarctica," said lead author Michael Kaplan, a geochemist at Columbia University's Lamont-Doherty Earth Observatory. "Knowing that the Younger Dryas cooling in the northern hemisphere was not a global event brings us closer to understanding how Earth finally came out of the ice age."
Ice core records show that warming of the southern hemisphere, starting 13,000 years ago, coincided with rising levels of the heat-trapping gas, carbon dioxide (CO2). The study is the first to link this spike in CO2 to the impressive shrinking of glaciers in New Zealand. The scientists estimate that glaciers lost more than half of their extent over a thousand years, and that their creep to higher elevations was a response to the local climate warming as much as 1 degree C.