Changing Ice,
Changing
Coastlines
Unabated climate change will lead to profound changes on our planet, perhaps none more so than the swelling of our seas and alteration of our coasts. About one out of three people in the world–and more than half of all Americans–live within 60 miles (ca. 100 km) of the ocean. Of these, some 600 million live in coastal areas less than 30 feet (ca. 9 m) above sea level.
Changing Ice,
Changing
Coastlines
Unabated climate change will lead to profound changes on our planet, perhaps none more so than the swelling of our seas and alteration of our coasts. About one out of three people in the world–and more than half of all Americans–live within 60 miles (ca. 100 km) of the ocean. Of these, some 600 million live in coastal areas less than 30 feet (ca. 9 m) above sea level.
The extent to which our planet's massive polar ice sheets will respond to warming air and ocean temperatures remains one of the largest uncertainties in climate-model predictions of future sea-level rise.
Our scientists are determined to reduce this uncertainty, and have taken their instruments to some of the world's most remote and extreme environments. One such place is the massive West Antarctic Ice Sheet (WAIS), which holds enough ice to raise global sea level by about 12 feet (ca. 3.7 m) if it were to melt completely. WAIS is considered to be highly vulnerable to climate change because so much of it rests on bedrock thousands of meters below sea level, in contact with the warming waters of the Southern Ocean. Just how vulnerable? That's what Jonathan Kingslake, Jacqueline Austermann, and Benjamin Keisling have set out to answer. They're part of an international team of researchers drilling more than a kilometer through WAIS and into ancient sediments deposited during times in Earth's history when temperatures were as warm as those we expect to see in the coming decades. The sediment cores will shed light on how much of WAIS actually melted during these warmer periods. The new data will help reduce uncertainty in climate models and could reveal if there is a tipping point in our climate system that could cause large amounts of land-based ice to melt and oceans to rise swiftly.
The extent to which our planet's massive polar ice sheets will respond to warming air and ocean temperatures remains one of the largest uncertainties in climate-model predictions of future sea-level rise.
Our scientists are determined to reduce this uncertainty, and have taken their instruments to some of the world's most remote and extreme environments. One such place is the massive West Antarctic Ice Sheet (WAIS), which holds enough ice to raise global sea level by about 12 feet (ca. 3.7 m) if it were to melt completely. WAIS is considered to be highly vulnerable to climate change because so much of it rests on bedrock thousands of meters below sea level, in contact with the warming waters of the Southern Ocean. Just how vulnerable? That's what Jonathan Kingslake, Jacqueline Austermann, and Benjamin Keisling have set out to answer. They're part of an international team of researchers drilling more than a kilometer through WAIS and into ancient sediments deposited during times in Earth's history when temperatures were as warm as those we expect to see in the coming decades. The sediment cores will shed light on how much of WAIS actually melted during these warmer periods. The new data will help reduce uncertainty in climate models and could reveal if there is a tipping point in our climate system that could cause large amounts of land-based ice to melt and oceans to rise swiftly.
Working in a different section of WAIS known as Whillans Ice Stream, Chloe Gustafson, Kerry Key and others used surface-based imaging instruments to create the first-ever map of a massive groundwater system circulating far under the Antarctic ice. The confirmation of the existence of deep groundwater dynamics has transformed our understanding about the behavior of ice streams, which are regions of fast flow within an ice sheet. These systems, probably common in Antarctica, could cause some ice sheets to hasten their march toward the sea, depending on how the groundwater reservoir reacts to warming ocean water and thinning ice.
The reasons for the transition from 41,000-year glacial cycles to 100,000-year glacial cycles and the intensification of ice ages that occurred about a million years ago has long puzzled climate scientists. Maayan Yehudai, Steven Goldstein, Joohee Kim, Karla Knudson, Louise Bolge, and Alberto Malinverno may have found the answer. Their analysis of deep-sea sediment cores taken in the north Atlantic, where ancient waters passed by and left chemical clues, provide evidence that each new ice age removed layers of ‘slippery’ continental soils. This exposed the 'stickier' crystalline bedrock underneath, causing ice sheets to cling more tightly to their beds, grow thicker and become more stable, thus triggering cycles of significantly longer and colder ice ages.
As sea levels rise, so does the risk of flooding and storm surges to coastline communities. Polar scientist Marco Tedesco and colleagues at Columbia’s Center for International Earth Science Information Network have created a new dataset that combines information about social vulnerability with data on mortgages, evictions, and threats from climate change for the entire US. Their work could help identify communities where vulnerable groups are at risk of being pushed out by rising flood-insurance rates and real estate values. The group has made the new dataset freely available to other researchers interested in exploring issues at the crossroads of racial, social, and climate justice.
How high did sea levels rise during the most recent warm period in Earth's history? Using sophisticated measurements made across the Bahamas, a Lamont team concluded that seas peaked at least 4 feet (ca. 1.2 m) higher than today. While still daunting, these levels are much lower than previous estimates, and are roughly in line with what most current models project for the next 100 years. Scroll down for a more detailed look at this research.
Working in a different section of WAIS known as Whillans Ice Stream, Chloe Gustafson, Kerry Key and others used surface-based imaging instruments to create the first-ever map of a massive groundwater system circulating far under the Antarctic ice. The confirmation of the existence of deep groundwater dynamics has transformed our understanding about the behavior of ice streams, which are regions of fast flow within an ice sheet. These systems, probably common in Antarctica, could cause some ice sheets to hasten their march toward the sea, depending on how the groundwater reservoir reacts to warming ocean water and thinning ice.
The reasons for the transition from 41,000-year glacial cycles to 100,000-year glacial cycles and the intensification of ice ages that occurred about a million years ago has long puzzled climate scientists. Maayan Yehudai, Steven Goldstein, Joohee Kim, Karla Knudson, Louise Bolge, and Alberto Malinverno may have found the answer. Their analysis of deep-sea sediment cores taken in the north Atlantic, where ancient waters passed by and left chemical clues, provide evidence that each new ice age removed layers of ‘slippery’ continental soils. This exposed the 'stickier' crystalline bedrock underneath, causing ice sheets to cling more tightly to their beds, grow thicker and become more stable, thus triggering cycles of significantly longer and colder ice ages.
As sea levels rise, so does the risk of flooding and storm surges to coastline communities. Polar scientist Marco Tedesco and colleagues at Columbia’s Center for International Earth Science Information Network have created a new dataset that combines information about social vulnerability with data on mortgages, evictions, and threats from climate change for the entire US. Their work could help identify communities where vulnerable groups are at risk of being pushed out by rising flood-insurance rates and real estate values. The group has made the new dataset freely available to other researchers interested in exploring issues at the crossroads of racial, social, and climate justice.
How high did sea levels rise during the most recent warm period in Earth's history? Using sophisticated measurements made across the Bahamas, a Lamont team concluded that seas peaked at least 4 feet (ca. 1.2 m) higher than today. While still daunting, these levels are much lower than previous estimates, and are roughly in line with what most current models project for the next 100 years. Scroll down for a more detailed look at this research.
Some Past Sea Levels May Not Have Been as High as Thought, Says Study of Rising and Sinking Landmasses
By Kevin Krajick
One big mystery of climate science surrounds widely accepted evidence that during the planet’s most recent warm interglacial period, ending about 117,000 years ago, global sea levels peaked as high as 9 meters (ca. 30 ft) higher than today. Back then, temperatures were about 2 degrees C warmer than those of preindustrial times, a mark we may surpass by century’s end, if not sooner. Yet, models of future sea level rise hover around a meter or so within the next 100 years. What are we missing, and how much should it scare us?
A study by Lamont scientists offers an answer. It says that previous research into past sea levels may have failed to accurately correct for long-term ups and downs of the land itself. Based on new measurements made across the Bahamas, the researchers produced lower—though still daunting—estimates for the last interglacial. They say seas peaked at least 1.2 meters (ca. 4 ft) higher than today, with an unlikely upper limit of 5.3 meters (ca. 17 ft).
“To get to 9 meters of sea level rise, you’d have to melt large parts of Greenland and Antarctica,” said lead author and former Lamont postdoctoral research scientist Blake Dyer. “This suggests that didn’t happen. So maybe we should feel not as bad about the future. On the other hand, our lower estimate is bad, and our upper one is really bad.”
Key to the study: as ice sheets build, they depress the land beneath them. But the Earth is elastic. What goes down in one place goes up someplace else, as when you squeeze a rubber ball. Corollary deformations outside the icy regions may creep for hundreds or thousands of miles over hundreds or thousands of years, moving mainly through the planet’s pliable mantle. When ice melts, the process goes in reverse, as previously ice-covered regions rebound, while those on the fringes sink, in seesaw fashion.
Such movements, known as glacial isostatic rebound, can skew estimates of past water levels, and scientists have struggled to adjust for them. Previous studies have suggested that topographic ripples from North America’s glaciations have traveled down all the way to the Bahamas, but exactly on what scale is uncertain.
To find out more, the researchers trekked along the coasts of seven islands, measuring the elevations of fossil coral reefs; fossilized edges of ancient beaches, nearshore sand deposits, and fossil dunes. They found similar sequences of similar ages on each island—but the elevations varied according to latitude. This meant the variations could not have been produced by water levels alone; movements of the land had to be considered. Putting all the measurements together, they concluded that islands to the north probably sank as much as 10 meters (ca. 33 ft) during the interglacial, while those to the south sank only about 6 meters (ca. 20 ft). They combined these findings with hundreds of different models of glacial isostatic rebound, and this produced the new, lower sea-level estimates.
One catch: evidence for the much higher estimates comes from the Mediterranean, the Indian Ocean and Australia. This hints that, among other things, we may be missing information about the size and distribution of ice sheets preceding the last interglacial. “Models of ice sheets are still in their toddlerhood,” said Lamont director and study coauthor Maureen Raymo. “The easy thing to say would be, ‘Oh we showed that sea levels were not so bad, and that’s terrific.’ The harder answer, the more honest answer, is that maybe things were different then, and we’re not in the clear.”
To improve their answers, the researchers plan to re-examine past sea-level markers along the coasts of Denmark, France, England, and South Africa.
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Some Past Sea Levels May Not Have Been as High as Thought, Says Study of Rising and Sinking Landmasses
By Kevin Krajick
One big mystery of climate science surrounds widely accepted evidence that during the planet’s most recent warm interglacial period, ending about 117,000 years ago, global sea levels peaked as high as 9 meters (ca. 30 ft) higher than today. Back then, temperatures were about 2 degrees C warmer than those of preindustrial times, a mark we may surpass by century’s end, if not sooner. Yet, models of future sea level rise hover around a meter or so within the next 100 years. What are we missing, and how much should it scare us?
A study by Lamont scientists offers an answer. It says that previous research into past sea levels may have failed to accurately correct for long-term ups and downs of the land itself. Based on new measurements made across the Bahamas, the researchers produced lower—though still daunting—estimates for the last interglacial. They say seas peaked at least 1.2 meters (ca. 4 ft) higher than today, with an unlikely upper limit of 5.3 meters (ca. 17 ft).
“To get to 9 meters of sea level rise, you’d have to melt large parts of Greenland and Antarctica,” said lead author and former Lamont postdoctoral research scientist Blake Dyer. “This suggests that didn’t happen. So maybe we should feel not as bad about the future. On the other hand, our lower estimate is bad, and our upper one is really bad.”
Key to the study: as ice sheets build, they depress the land beneath them. But the Earth is elastic. What goes down in one place goes up someplace else, as when you squeeze a rubber ball. Corollary deformations outside the icy regions may creep for hundreds or thousands of miles over hundreds or thousands of years, moving mainly through the planet’s pliable mantle. When ice melts, the process goes in reverse, as previously ice-covered regions rebound, while those on the fringes sink, in seesaw fashion.
Such movements, known as glacial isostatic rebound, can skew estimates of past water levels, and scientists have struggled to adjust for them. Previous studies have suggested that topographic ripples from North America’s glaciations have traveled down all the way to the Bahamas, but exactly on what scale is uncertain.
To find out more, the researchers trekked along the coasts of seven islands, measuring the elevations of fossil coral reefs; fossilized edges of ancient beaches, nearshore sand deposits, and fossil dunes. They found similar sequences of similar ages on each island—but the elevations varied according to latitude. This meant the variations could not have been produced by water levels alone; movements of the land had to be considered. Putting all the measurements together, they concluded that islands to the north probably sank as much as 10 meters (ca. 33 ft) during the interglacial, while those to the south sank only about 6 meters (ca. 20 ft). They combined these findings with hundreds of different models of glacial isostatic rebound, and this produced the new, lower sea-level estimates.
One catch: evidence for the much higher estimates comes from the Mediterranean, the Indian Ocean and Australia. This hints that, among other things, we may be missing information about the size and distribution of ice sheets preceding the last interglacial. “Models of ice sheets are still in their toddlerhood,” said Lamont director and study coauthor Maureen Raymo. “The easy thing to say would be, ‘Oh we showed that sea levels were not so bad, and that’s terrific.’ The harder answer, the more honest answer, is that maybe things were different then, and we’re not in the clear.”
To improve their answers, the researchers plan to re-examine past sea-level markers along the coasts of Denmark, France, England, and South Africa.
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Donate today to SUPPORT LAMONT SCIENCE
Editors: Francesco Fiondella, Marian Mellin, Stacey Vassallo I Contributing Writers: Kevin Krajick, Sarah Fecht, Marie DeNoia Aronsohn I Design: Carmen Neal
Columbia Climate School Lamont-Doherty Earth Observatory Annual Report FY2022
© 2022 by The Trustees of Columbia University in the City of New York, Lamont-Doherty Earth Observatory. All rights reserved.
Editors: Francesco Fiondella, Marian Mellin, Stacey Vassallo I Contributing Writers: Kevin Krajick, Sarah Fecht, Marie DeNoia Aronsohn I Design: Carmen Neal
Columbia Climate School Lamont-Doherty Earth Observatory Annual Report FY2022
© 2022 by The Trustees of Columbia University in the City of New York, Lamont-Doherty Earth Observatory. All rights reserved.
