Degradation of the North American ice cap has reduced climate variability in the southern hemisphere

New research from the University of Colorado at Boulder shows that the changing topography of the ice caps in the northern hemisphere during the last ice age forced changes in the climate of Antarctica, a mechanism of interpolar climate change hitherto undocumented.

The new study published today in the journal Nature and co-authored by researchers at the University of Bristol, the University of Washington and UC Berkeley – suggests that a substantial reduction in the Laurentian ice sheet that covered much of present-day North America around 16,000 years ago resulted in significant climatic variations in the tropical Pacific and West Antarctica.

“The results demonstrate how effects apparently localized in one part of the world can have a significant impact on the climate elsewhere on Earth,” said Tyler Jones, associate researcher at the CU Boulder Institute for Arctic and Alpine Research (INSTAAR) and lead author of the new study.

Jones and his colleagues studied an ice core taken from the West Antarctic Ice Sheet (WAIS) to document the historic climate. The WAIS ice core is the first climate record to preserve year-to-year climate variability continuously 30,000 years ago.

“This ice core is really important because it contains long-term climate information that relates to the timescales humans experience and remember,” Jones said.

At INSTAAR’s Stable Isotope Lab, researchers slowly melted and then vaporized the ice cores for analysis using laser absorption spectroscopy, a new methodology that reveals the isotopic composition of water . This method improved the ability of researchers to measure climate change through ice cores, both increasing measurement resolution and saving time.

When the researchers examined the magnitude of year-over-year climate signals preserved in the WAIS core, they noticed a large and abrupt decline in signal strength about 16,000 years ago. They later determined that the anomaly was largely caused by the lowering of the Laurentian ice sheet.

“When there is a large ice cap over North America, the circulation of the atmosphere becomes very different from today,” Jones said. The new findings corroborate another published study suggesting that changes in the ice sheet over the same period altered the tropical Pacific climate enough to transform land ecosystems in present-day Indonesia from a grassy savannah to a rainforest, that they remain today.

Overall, the study points out that changes in Earth’s climate system can be linked over vast distances.

“No one has really studied this type of signal before. It potentially opens up new and exciting ways of thinking about climate data,” Jones said.