By Allison Chinchar, CNN Meteorologist
In an ever-warming climate, ripple effects or chain reactions could lead to altered weather patterns across the globe thanks to a melting Antarctic ice sheet, a new study says.
Alessandro Dahan/Getty Images This small lake was formed by melting ice. In the background are the ice sheets on a hill next to Comandante Ferraz Station, on January 5, 2020, in King George Island, Antarctica.
The study, published in the journal Nature Geoscience, found that as Earth continues to heat up, the land underneath the Antarctic ice sheet will become more exposed. As a result of that process, wind patterns will shift, and rainfall will increase over Antarctica, which could trigger processes that speed up ice loss.
"We found that ice sheet retreat exposing previously ice-covered land led to big increases in rainfall, which through a feedback mechanism dramatically warms the ocean," Catherine Bradshaw, senior scientist at the UK Met Office and lecturer at the University of Exeter told CNN.
"This feedback mechanism could potentially trigger additional processes that accelerate ice loss."
The joint study is based on combining climate modeling and data comparisons from the Middle Miocene epoch (13-17 million years ago).
Why do we care about something that happened more than 13 million years ago? Because carbon dioxide levels and global temperatures during the Middle Miocene were similar to those Earth is forecast to reach by the end of this century.
When it rains it pours
"With the big ice sheet on Antarctica like we have today, the predominant winds are known as katabatic winds, and these go from the land to the sea," Bradshaw told CNN. "They originate from the ice sheet where it is very high, very cold and very dry -- in fact Antarctica receives only a few inches of snowfall a year and is so dry it is classified as a desert."
Bradshaw cautions that those winds could actually reverse -- blowing instead from the cooler sea to the warmer, drier land -- if Antarctica continues to warm. Generating the same results we see from daily sea breezes as well as seasonal monsoon winds that occur around the world.
A monsoon is simply a seasonal reversal of wind direction which results in changes in precipitation for a specific region of the globe. For Antarctica, this means an increase in rain.
"The surface of the Antarctic ice sheet is very bright, and it reflects some 50-80% of the sunlight that hits it. Where the ice sheet retreats and exposes the darker land surface underneath, this ground is much less reflective and so absorbs more sunlight, which warms it up," Bradshaw told CNN.
Bradshaw explained that ice-free ground at the coast warms up more than the surrounding sea surface which in turn causes the change in wind direction. Similar to the seas breezes Florida experiences, these winds can bring in moisture from the surrounding ocean that can dramatically increase rainfall.
"What happens to an ice sheet when rainfall increases depends on where the rain falls and whether it is cold enough to fall as snow instead of rain." said Bradshaw.
"If the temperatures are warm enough for the moisture to fall as rain over the ice-free area, this could trigger processes that can accelerate ice loss. Conversely, if the temperatures are cold enough for the moisture to fall as snow over the ice sheet, this can cause ice growth."
As the Earth continues to warm, scientists may be able to learn from monsoonal regions of the world about how to prevent a collapse of the Antarctic ice sheet. While that may sound a little far-fetched, this new research shows it may have actually happened in the past when the Antarctic ice sheet was even more unstable.
"Essentially, if more land is exposed in Antarctica, it becomes harder for a large ice sheet to reform, and without (favorable) orbital positions in the Middle Miocene playing a role, perhaps the ice sheet would have collapsed at that time," Bradshaw said in a news release.
While the study suggests that the Antarctic ice sheet was capable of major advance and retreat across the continent during the Middle Miocene, Dr Bradshaw emphasizes that conditions now are not identical to those millions of years ago.
"It is important to stress that there were many important processes not included in our study, which, considering our findings, require additional research to establish exactly what the implications are for the future," Bradshaw told CNN. "This is the work that I intend to do next, but have not yet started."
Walking on thin ice
Additional rainfall on the Antarctic continent isn't just about the local impacts, but also global ones -- since that new rainfall would eventually cause more freshwater to end up in the surrounding oceans in turn causing sea levels to rise.
"Rain ultimately flows back to sea, and because it is freshwater rather than saltwater, it is less dense than the seawater it is draining into," Bradshaw told CNN. "This means it can form a cap at the surface rather than sinking and circulating."
This is important because you have now essentially created a separation point between the deep ocean and the surface of the ocean which leads the deep waters to warm up.
"Since much of the West Antarctic ice sheet in particular is grounded beneath the sea surface, warmer waters can interact with the ice sheet from beneath, " said Bradshaw.
"If the surface of the ice sheet is melting it can form meltwater lakes that rainfall can add to. Meltwater lakes tend to be blue rather than white, making them darker than the ice underneath and therefore they absorb more sunlight, which makes them warmer."
This can create a domino effect in which these darker, warmer waters could cause the ice sheet to melt from the inside out. So the worst-case scenario now is the ice sheet not only melting from within -- but also shrinking at the coastline.
"Near the coast, the ice flows faster in ice streams, glaciers and ice shelves and is lost to the ocean as either meltwater or icebergs," Bradshaw told CNN. "Without new snowfall to replace the ice that is constantly being lost, the ice sheet will lose mass."
Even though this study focused mainly on Antarctica there have also been noticeable changes in ocean temperatures and salinity not only in the Southern Hemisphere but also in the Northern Hemisphere due to melting from Greenland's ice sheet.
This dramatic melting of the world's ice sheets could lead to dramatic changes in weather patterns. Exactly how stable or unstable the Antarctic ice sheet is, is still not fully determined. However one thing is certain and that is that the ice is constantly moving.
The study, published in the journal Nature Geoscience, found that as Earth continues to heat up, the land underneath the Antarctic ice sheet will become more exposed. As a result of that process, wind patterns will shift, and rainfall will increase over Antarctica, which could trigger processes that speed up ice loss.
"We found that ice sheet retreat exposing previously ice-covered land led to big increases in rainfall, which through a feedback mechanism dramatically warms the ocean," Catherine Bradshaw, senior scientist at the UK Met Office and lecturer at the University of Exeter told CNN.
"This feedback mechanism could potentially trigger additional processes that accelerate ice loss."
The joint study is based on combining climate modeling and data comparisons from the Middle Miocene epoch (13-17 million years ago).
Why do we care about something that happened more than 13 million years ago? Because carbon dioxide levels and global temperatures during the Middle Miocene were similar to those Earth is forecast to reach by the end of this century.
When it rains it pours
"With the big ice sheet on Antarctica like we have today, the predominant winds are known as katabatic winds, and these go from the land to the sea," Bradshaw told CNN. "They originate from the ice sheet where it is very high, very cold and very dry -- in fact Antarctica receives only a few inches of snowfall a year and is so dry it is classified as a desert."
Bradshaw cautions that those winds could actually reverse -- blowing instead from the cooler sea to the warmer, drier land -- if Antarctica continues to warm. Generating the same results we see from daily sea breezes as well as seasonal monsoon winds that occur around the world.
A monsoon is simply a seasonal reversal of wind direction which results in changes in precipitation for a specific region of the globe. For Antarctica, this means an increase in rain.
"The surface of the Antarctic ice sheet is very bright, and it reflects some 50-80% of the sunlight that hits it. Where the ice sheet retreats and exposes the darker land surface underneath, this ground is much less reflective and so absorbs more sunlight, which warms it up," Bradshaw told CNN.
Bradshaw explained that ice-free ground at the coast warms up more than the surrounding sea surface which in turn causes the change in wind direction. Similar to the seas breezes Florida experiences, these winds can bring in moisture from the surrounding ocean that can dramatically increase rainfall.
"What happens to an ice sheet when rainfall increases depends on where the rain falls and whether it is cold enough to fall as snow instead of rain." said Bradshaw.
"If the temperatures are warm enough for the moisture to fall as rain over the ice-free area, this could trigger processes that can accelerate ice loss. Conversely, if the temperatures are cold enough for the moisture to fall as snow over the ice sheet, this can cause ice growth."
As the Earth continues to warm, scientists may be able to learn from monsoonal regions of the world about how to prevent a collapse of the Antarctic ice sheet. While that may sound a little far-fetched, this new research shows it may have actually happened in the past when the Antarctic ice sheet was even more unstable.
"Essentially, if more land is exposed in Antarctica, it becomes harder for a large ice sheet to reform, and without (favorable) orbital positions in the Middle Miocene playing a role, perhaps the ice sheet would have collapsed at that time," Bradshaw said in a news release.
While the study suggests that the Antarctic ice sheet was capable of major advance and retreat across the continent during the Middle Miocene, Dr Bradshaw emphasizes that conditions now are not identical to those millions of years ago.
"It is important to stress that there were many important processes not included in our study, which, considering our findings, require additional research to establish exactly what the implications are for the future," Bradshaw told CNN. "This is the work that I intend to do next, but have not yet started."
Walking on thin ice
Additional rainfall on the Antarctic continent isn't just about the local impacts, but also global ones -- since that new rainfall would eventually cause more freshwater to end up in the surrounding oceans in turn causing sea levels to rise.
"Rain ultimately flows back to sea, and because it is freshwater rather than saltwater, it is less dense than the seawater it is draining into," Bradshaw told CNN. "This means it can form a cap at the surface rather than sinking and circulating."
This is important because you have now essentially created a separation point between the deep ocean and the surface of the ocean which leads the deep waters to warm up.
"Since much of the West Antarctic ice sheet in particular is grounded beneath the sea surface, warmer waters can interact with the ice sheet from beneath, " said Bradshaw.
"If the surface of the ice sheet is melting it can form meltwater lakes that rainfall can add to. Meltwater lakes tend to be blue rather than white, making them darker than the ice underneath and therefore they absorb more sunlight, which makes them warmer."
This can create a domino effect in which these darker, warmer waters could cause the ice sheet to melt from the inside out. So the worst-case scenario now is the ice sheet not only melting from within -- but also shrinking at the coastline.
"Near the coast, the ice flows faster in ice streams, glaciers and ice shelves and is lost to the ocean as either meltwater or icebergs," Bradshaw told CNN. "Without new snowfall to replace the ice that is constantly being lost, the ice sheet will lose mass."
Even though this study focused mainly on Antarctica there have also been noticeable changes in ocean temperatures and salinity not only in the Southern Hemisphere but also in the Northern Hemisphere due to melting from Greenland's ice sheet.
This dramatic melting of the world's ice sheets could lead to dramatic changes in weather patterns. Exactly how stable or unstable the Antarctic ice sheet is, is still not fully determined. However one thing is certain and that is that the ice is constantly moving.
© Mario Tama/Getty Images The western edge of the giant iceberg A-68, calved from the Larsen C ice shelf, is seen from NASA's Operation IceBridge research aircraft, near the coast of the Antarctic Peninsula region, in 2017.
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