By Peggy Helman
Medill News Service, Dec. 17, 2024
Towering over the Peruvian town of Yunguy, Mount Huascarán stands at a staggering 22,205 feet (6,768 meters) above sea level, making it the tallest mountain in Peru. The snow-capped behemoth is popular among mountain climbers, tourists – and scientists.
That’s because ice frozen deep inside the tropical glacier may hold the key to understanding atmospheric temperature changes on a global scale.
“It’s important we understand the past, not just the future,” said Yuntao Bao, an atmospheric scientist at Ohio State University who led cutting edge research on climate secrets nestled in Huascarán’s ice cores. The research took Bao and other researchers climbing Huascarán’s icy peaks to find those secrets.
Peru’s climate, like much of the tropics, is heavily influenced by convection currents and heavy rainfall. This has led past researchers to use records from this region as indicators of global mean moisture and precipitation.
However, Huascarán’s peak is at such a high elevation that it experiences a dry and frigid climate. These high tropical alpine glaciers provide a distinct paleoclimate record for climate changes in the middle and upper troposphere – the layer of atmosphere where humans live.
The climatic interpretation of a key proxy, the ratio of stable water oxygen and a heavier oxygen isotope remains an outstanding problem in tropical mountains.
And so, Bao and his team set out to solve it.
The team led by Lonnie Thompson, a senior research scientist at the Ohio State University, drilled into Huascarán and harvested an ice core, named ice core δ18O.
The team including Bao measured carbon dioxide trapped in the core’s air bubbles to figure out date markers. Once dated, they sliced each core into smaller cross sections based on their age markers, so each slice corresponded to a different period of time.
Next, they melted down one cross section at a time into water. Then, they used a mass spectrometer to measure the core’s stable water isotopes, a ratio between heavy water, which has heavier oxygen isotopes, and light water, which has common oxygen. More depleted isotopes indicate a lower temperature, and a higher presence of isotopes indicates a higher temperature.
These measurements were then compared with proxy data and records.
Bao found that the heavy oxygen isotope (δ18O) in the ice core is a robust indicator of air temperature – not precipitation, as previously believed – during deglaciation about 11,000 to 20,000 years ago and is defined by increasing CO2 and decreasing ice sheet cover.
Based on this data, we can estimate how much cooling leading up to present day and heat driven by carbon dioxide and ice sheet change. Looking at the ice core, Bao estimates the Earth’s temperature has warmed an average of six degrees in the last 20,000 years since the Last Glacial Maximum, the maximum range of the ice age. That confirms other data about temperature change between ice ages and warm spells. However, climate change due to fossil fuel emissions in the industrial age has pushed temperatures beyond that range by an estimated 1.5 degrees Centigrade (2.7 degrees Fahrenheit).
Because industrialization happened so recently in Earth’s history, scientists and researchers only have about 100 years of instrument-measured data to work with. Bao’s research focuses on paleoclimate modeling, which helps scientists fill in data gaps from the pre-industrial era.
Meredith Kelly, a scientist and professor at Dartmouth College says Bao’s findings support her own work with tropical ice cores in Costa Rica.
“It shows that temperatures cooled at high elevations during the LGM more than they did at low elevations,” Kelly said.
Although Bao’s research provides new ways to gather paleoclimate data using oxygen isotopes from land mass rather than marine sources, much work is left to be done to fully understand why the Earth has cooled and heated in the way that it has.
“There certainly need to be more sites,” Kelly said.
Bao presented his research at the Comer Climate Conference, hosted annually in southwestern Wisconsin by the Comer Science and Education Foundation. Like Bao, many of the scientists who presented their findings on oceans, sea level rise and melting ice at the conference probed deep into Earth’s complex past in search of solutions for the climate crisis. from land
“With paleoclimate, either from proxy data and from climate modeling, we can get more extended data, through hundreds of thousands of years and understand the mechanism of this past climate change. And, we can constrain how much future climate change there will be,” Bao said.
Photo at top: The view of Mount Huascarán from Yungay, Peru. (Wikimedia Commons)
