Measuring the loss of earth's frozen regions.
Oliver Frauenfeld's goal is to project what the holistic cryosphere will look like through the year 2100.
For the first time, climatologists have measured just how much Earth’s frozen regions—known collectively as the cryosphere—have shrunk since 1979.
“You keep hearing in the news media that the cryosphere is disappearing,” says Oliver Frauenfeld, associate professor in the College of Arts & Sciences. “It occurred to us that no one had ever looked at the cryosphere as a whole and measured what is happening.”
This might seem like a straightforward task.
“Once you look at the task more closely, it gets very complicated,” Frauenfeld says
Photo: NASA / Kathryn Hansen
For example: What exactly is the cryosphere?
“There are lots of definitions out there,” Frauenfeld says. “Some define it as any place where air temperatures are below freezing. Some define it as any place that contains frozen water.”
In the end, the researchers found their definition through publicly available data from around the world.
“We had access to continuous satellite data that tells us where Earth’s ground is frozen,” Frauenfeld says.
“We also had data that detects the presence or absence of snow cover. And we had data on the frozen areas of the ocean. Those were the three variables we decided to concentrate on: frozen ground, snow cover and sea ice.”
As a second challenge, the research team had to overcome a lack of dependable data about the cryosphere south of the equator. To fill such gaps, climatologists apply a method known as “reanalysis” to simulate past changes in the planet’s surface and atmosphere over several decades based on available data and observations.
We have reliable snow-cover observations from the Northern Hemisphere, but nothing like that exists for the Southern Hemisphere,” Frauenfeld says. “So, we depended on interim reanalysis, using data from the European Centre for Medium-Range Weather Forecasts. For sea ice and frozen ground, we rely on products from the National Snow and Ice Data Center, which come from NASA’s satellite data sets.
Each year, our planet’s cryosphere shrinks by an average
The total loss over 37 years comes to more than
All told, it took a year to complete the study, including three months to publish it in Earth’s Future, a journal of the American Geophysical Union. Frauenfeld joined with long-time collaborator Xiaoqing Peng to perform the study.
Using data from 1979-2016, the study confirms conventional wisdom: The cryosphere is indeed shrinking. However, the study also tells us how much it’s shrinking over time.
Each year, our planet’s cryosphere shrinks by an average of 33,000 square miles. That’s an area about the size of Maine.
The total loss over 37 years comes to more than 1.2 million square miles. That’s enough cryosphere to cover India. Moreover, the study says, the growth season for the world’s cryosphere is now eight days shorter than in 1979.
The study also revealed something that climatologists knew but had never quantified: The world’s northern cryosphere is shrinking, but its southern counterpart is expanding. While the Northern Hemisphere loses 39,000 square miles of cryosphere each year, the Southern Hemisphere gains almost 6,000 square miles due to the long-term expansion of sea ice around Antarctica’s ice sheet.
In Fall 2022, Frauenfeld expects to follow up with a second study that will predict the cryosphere’s long-term future.
“I’m interested in using climate model projections to essentially repeat our first study, based on the climate data that are available,” he says. “We can tease out some useful cryospheric projections for the future.”
The second study will echo the first one by forecasting changes in the same three variables: frozen ground, snow cover and sea ice. “My goal,” Frauenfeld says, “is to project what the holistic cryosphere will look like through the year 2100.”
This story was first reported by the former College of Geosciences, now part of the College of Arts & Sciences.
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