LOW TIDES MAY ADD TO MASSIVE COLLAPSE OF GREENLAND GLACIERS

LOW TIDES MAY ADD TO MASSIVE COLLAPSE OF GREENLAND GLACIERS

Courtesy of Meredith Nettles Calving front of the Helheim Glacier in Greenland. Low tides may be adding to the stress of ice collapsing from glaciers such as the Helheim.
Courtesy of Meredith Nettles
Calving front of the Helheim Glacier in Greenland. Low tides may be adding to the stress of ice collapsing from glaciers such as the Helheim.

by Katherine Dempsey
Nov 18, 2014

Global warming is driving increased calving of the Greenland glaciers, causing icebergs the size of Central Park to crash into the sea. But low tides might be contributing to the calving crisis and helping to trigger huge earthquakes created by the massive icebergs, according to seismologist Meredith Nettles.

Nettles, of Columbia University, shared her latest findings with other leading climate scientists at the Comer Abrupt Climate Change Conference held in southwestern Wisconsin this fall. She showed her latest data about calving, the process of massive icebergs collapsing off of glaciers with increasing losses due to climate change. Nettles studies calving in Greenland and the “glacial earthquakes” that radiate seismic signals all the way to New Mexico.

Glacial earthquakes, which Nettles and a colleague first discovered in 2003, happen when a massive calving event occurs. In 2013, a record number of glacial earthquakes rocked Greenland compared to records kept since 1993. These magnitude-5 quakes can be detected even farther south than New Mexico, Nettles said. The seismic signals provide a sort of clock to indicate when calving takes place and Nettles also measures the velocities of glaciers with GPS receivers. 

“One thing that’s been really useful about the earthquakes is to be able to say we know to the minute when this calving event happened,” Nettles said. “We can say, ‘Okay, the calving happened at this time and the speed-up happened at this time.’”

Enter the tides. Evidence suggests that calving affects how quickly glaciers overall weaken and move forward into the ocean, so it’s key to figure out what’s involved in the process, Nettles told conference scientists. And that’s what she is doing. 

Abigail Foerstner/MEDILL Seismologist Meredith Nettles studies huge earthquakes that result from ice breaking off Greenland glaciers.
Abigail Foerstner/MEDILL
Seismologist Meredith Nettles studies huge earthquakes that result from ice breaking off Greenland glaciers.

 

She documented observations at Helheim Glacier in 2009, using six seismic stations positioned on rock, to pick up small earthquakes – presumably caused by the ice breaking – in 30-second intervals. She and her team noticed that the earthquakes occurred in 12-hour cycles, similar to the tide. Comparing the occurrence of the earthquakes to tides revealed an anti-correlation – a low tide corresponded to a greater number of earthquakes than with a high tide.

Tides result from forces applied by the moon and sun. Most coastal places encounter two high and two low tides each lunar day. A lunar day – 24 hours and 50 minutes – signifies how long it takes for a location on Earth to rotate from a point under the moon and return to that spot under the moon. High tides happen every 12 hours and 25 minutes.

 

The parts of the earth pulled by the gravity of the moon as it orbits experience high tide. When the gravitational pull subsides, the tides retreat to low levels. 


Although Nettles is still working to determine the relationship between the low tides and the earthquakes, low tide does add more stress to pull on the glacier, she noted. It lets the ice stretch more, and stretching any material makes it break.

Photo by Gary Comer Low tides might be contributing to calving, the process of ice breaking off of glaciers.
Photo by Gary Comer
Low tides might be contributing to calving, the process of ice breaking off of glaciers.

 

Nettles pointed out that the flow of the glaciers changes as the tide changes. “When the tide is high, we have the position of the glacier retarded compared to mean,” she told scientists. When a low tide occurs, though, the glacier moves in advance of its average location.

Lots of stress from the tide creates strain in the glacier, she said. That strain may encourage calving. Calving models indicate that fragmenting the ice is necessary for an iceberg to separate, Nettles said, and small earthquakes seem to come from ice fracture or slip on shear faults.

Sea level increases as the ice sheet becomes smaller and its ice enters the ocean. That can create flooding and more severe storm surges, Nettles said.

A warmer world is linked to the shrinking ice sheets – more calving occurs when warmer water in the fjord makes contact with the glacier, she said. Understanding the process is critical as glaciers in the Arctic and Antarctic as well as in Greenland break apart.

If the West Antarctic Ice Sheet collapses, sea level would rise by about 11 feet on average across the earth. “There’s no question at all that the number of people and the amount of stuff that we have close to sea level is huge,” glaciologist Richard Alley said. “What happens to the beach, what happens to our shipping, what happens to our naval base?”

 

Alley – a top climate change researcher – discussed at the conference whether losing the West Antarctic Ice Sheet is in our future. Right now, the ice sheet is getting smaller, which drives sea level rise. Snowfall hits the surface of the sheet, and it spreads under its own weight and flows into the ocean. Typically, the ice does not calve off and create icebergs when it starts floating. It usually creates ice shelves that occupy coastal bays and fjords, he explained. Sea-floor high points and the fjord walls rub against the sides of the ice shelves, producing friction and slowing down how quickly the non-floating ice flows into the shelves, he noted. 

But melting, linked partially to climate change, is accelerating.

“Recently, warmer ocean waters have been circulating beneath some of the ice shelves, increasing melting and iceberg calving from them, reducing their friction and thus allowing the non-floating ice to flow more rapidly into the ocean, raising sea level,” Alley pointed out. Warmer waters have moved under the ice shelves due to varying winds, which probably result from global warming, the Antarctic ozone hole, and “natural variability,” he said.

ICE AGE PUZZLES IN CHILE HIDE MYSTERIES FOR WARMING WORLD

ICE AGE PUZZLES IN CHILE HIDE MYSTERIES FOR WARMING WORLD

NOAA The ice sheets extended well south of the Great Lakes at their maximum during the grip of the ice age 18,000 years ago
NOAA
The ice sheets extended well south of the Great Lakes at their maximum during the grip of the ice age 18,000 years ago

by Bryce Gray
Dec 01, 2014

Climate trends in the Northern and Southern hemispheres often seem out of sync, and scientists say that solving the mystery is a must to better understand what to expect in a warming world.

Enter George Denton, a veteran researcher on the shifts between the glacial and interglacial cycles – the ice ages and warm spells that crisscross Earth’s climate history. Denton, a University of Maine professor in the School of Earth and Climate sciences, searches for clues to glacial mysteries across the world and across time.

But understanding one “modal flip” that occurred around 18,000 years ago draws on decades of his research. “A dramatic collapse of ice” in Chile and New Zealand indicates that the Southern Hemisphere wrested itself from the planet’s last major glacial period while North America stood under mountains of ice, Denton says. 

Denton remains puzzled by a number of underlying questions associated with this sudden transition, he told colleagues at the Comer Abrupt Climate Change Conference held in southwestern Wisconsin this fall.

Medill photo George Denton's decades of research focusing on glacial moraines are filling in the puzzle pieces to understand how the Northern and Southern hemispheres react to climate change and influence each other.
Medill photo
George Denton’s decades of research focusing on glacial moraines are filling in the puzzle pieces to understand how the Northern and Southern hemispheres react to climate change and influence each other.

He is seeking elusive clues about what caused the shift and the geographic ripple in which the late glacial reversal reverberated around the planet. Piecing together the clues of planetary forces at work promises a better perspective of how human forcing of the climate through greenhouse gas emissions today will impact communities across the globe.

Denton detailed his studies of moraines – ridges left by glaciers – and other geologic deposits throughout the Southern Hemisphere to establish a timeline for glacial advances.

In the stunning glacial valleys of Chile’s Lake District, Denton’s fieldwork identified glacial advances between 18,000 and 38,000 years ago, a period when the glaciers in the Northern Hemisphere extended into southern Illinois.

After developing a chronological picture of that region’s glacial history, Denton later observed a similar timeline while studying moraines nestled at the foot of the Southern Alps of New Zealand’s Pukaki Valley, suggesting that the causal climatic trends extended across the hemisphere.

Although the intercontinental periods of glaciation matched up, Denton was intrigued by the fact that they could not be explained by the Milankovitch theory. That theory introduces another star player on the climate stage. It memorializes mathematician and astronomer Milutin Milankovitch, who died in 1958 and, without the aid of computers, calculated cyclical changes in climate that coincide with a combination of the gentle wobble of Earth’s tilt on its axis and changes in the elliptical shape of the planet’s orbit around the sun. These planetary changes impact temperature by altering the intensity of incoming solar radiation, or insolation.

Denton and his team plotted summer solar intensity “and we couldn’t see any correspondence,” he said. denton-3

Denton said that he and other climate scientists have long been dissatisfied with the Milankovitch theory’s assertion that changes in global climate must begin in the Northern Hemisphere, where large landmasses make the hemisphere more sensitive to changes in solar intensity. Despite this reasoning, southern glaciers historically seem to have been in relative synchrony with Northern Hemisphere glaciation, an inconsistency Denton says is a “fly in the ointment” of the Milankovitch theory.

“Summer intensity is not driving the glaciers in the Southern Alps, but it’s supposed to drive the glaciers in the Northern Hemisphere,” Denton said.

Although plotting the formation of southern moraines against insolation was inconclusive, Denton believes it is more likely that the glacial response was triggered by Heinrich events. These occur when a massive collapse of northern ice sheets into the sea disrupts the ocean’s circulatory system that brings warm equatorial waters north, throwing off a key switch regulating global climate.

“There’s a suspicion that somehow they’re related to Heinrich events,” said Denton, noting that such catastrophes bookend all of the moraine formations.

Despite the suggestion that Heinrich events may have had a role in glacial retreats in one hemisphere and advances half a world away, Denton said more research is required to fully understand how the climate shift of 18,000 years ago in the Southern Hemisphere was synced elsewhere around the globe and how widespread it was. 

“We see this in a great part of the Southern Hemisphere. Is it in the tropics? And what’s the situation in the Northern Hemisphere?” said Denton.

“These are the puzzles that I see that need to be worked out, using mountain glaciers all over the globe.”

SOIL ‘GIVES A KICK’ TO CLIMATE CHANGE

SOIL ‘GIVES A KICK’ TO CLIMATE CHANGE

Jeffrey Severinghaus Ice cores from the West Antarctic Ice Sheet. Scientists use these ice cores to measure the presence of carbon dioxide and other atmospheric gases during the last ice age.
Jeffrey Severinghaus
Ice cores from the West Antarctic Ice Sheet. Scientists use these ice cores to measure the presence of carbon dioxide and other atmospheric gases during the last ice age.

by Sarah Kramer
Nov 24, 2014

Yes, humans are releasing huge amounts of carbon dioxide into the atmosphere by burning fossil fuels. But we might be boosting the emissions from an unexpected place: the earth beneath our feet. 

Antarctic warming periods in the ancient past shows that soils may have amplified rises in temperature that occurred thousands of years ago. This could mean an unexpected wallop of excess CO2 into the atmosphere in response to global warming and decades of human fossil-fuel. 

“Humans are causing climate change,” said Dr. Jeffrey Severinghaus, “But Mother Nature’s going to give it a little kick.” 

Severinghaus, a professor at University of California-San Diego’s Scripps Institute of Oceanography, presented this research at the Comer Abrupt Climate Change Conference this fall. 

Climate scientists previously thought that atmospheric carbon dioxide rose gradually and steadily when natural sources like soil were involved. However, Severinghaus’ work with ice cores that trap ancient pockets of carbon dioxide show that the rising levels also occurs in abrupt jumps, suggesting that the Earth’s feedback might be magnifying other increases. About half of the carbon dioxide in the atmosphere after the last ice age was distributed in these jumps, he said. 

Jeffrey Severinghaus A scientist pulls out one of the West Antarctic ice cores. "Ice has a thermal memory," said Severinghaus, "the same way a cool cellar has a memory of winter."
Jeffrey Severinghaus
A scientist pulls out one of the West Antarctic ice cores. “Ice has a thermal memory,” said Severinghaus, “the same way a cool cellar has a memory of winter.”

The mismatch at times between the increase in temperature and the increase in carbon dioxide, Severinghaus said, is evidence of a “feedback loop” in the Earth’s natural carbon dioxide releases. He estimated that half of the rise in carbon dioxide levels during the natural warming period that began 18,000 years ago happened in “little jumps,” independent of air-temperature rise. 

“We think that these little jumps are telling us that soils do actually give off CO2 in a warming climate,” Severinghaus said. “We want to know if natural soils will give out excess CO2 in response to the warming caused by humans.” 

Comparing the Antarctic work to previous investigations on Greenland, Severinghaus and his team found that temperatures rose in the North Atlantic first, with the southern hemisphere warming starting nearly 200 years later. These increases in temperature are also linked to large releases of icebergs into the Atlantic, called Heinrich events.

“What’s really fascinating,” Severinghaus said, “Is that these events happen a long time before the warming.” 

Heinrich events are part of a pattern of a shifting global climate reaching back to the last ice age. Once icebergs are released en masse into the North Atlantic, the northern hemisphere cools and the southern hemisphere warms.

The precise timing of Heinrich events wasn’t known until an innovative research technique used by Severinghaus’ team. By melting ice cores and measuring the methane released, scientists could measure changes in atmosphere with unprecedented accuracy.

Jeffrey Severinghaus Blue ice on the West Antarctic Ice Sheet. Blue ice is formed when snowfall compresses to become part of the glacier.
Jeffrey Severinghaus
Blue ice on the West Antarctic Ice Sheet. Blue ice is formed when snowfall compresses to become part of the glacier.

Since methane is well mixed throughout the atmosphere, Severinghaus told fellow scientists, a record of a shift in the Antarctic means a shift worldwide. Carbon dioxide increases more slowly than methane and the air temperature.

Together with increased rain in the tropics and other events, Severinghaus said this shows that the Earth’s climate patterns can shift between states of cooling and warming but remain within a fairly narrow, stable range. The worry is that humans might be pushing these modes to the extreme, potentially launching the Earth into a new range of climate events.

“It’s possible that in this very complicated climate system there might be states that we accidentally discover,” Severinghaus said, “And that, all of a sudden, the climate might change dramatically in a few years.”

Despite the catastrophic messages ancient climates seem to be sending us, Severinghaus said that few people alive now will be around to see the all results of the carbon-dioxide feedback loop or disappearing glaciers. But we can expect to see coastal flooding, more severe storms and droughts—exacerbating starvation, resource conflicts and the problem of climate refugees as populations flee affected areas.

For the Midwest, alternation between extreme drought and heavier rainfall will lead to flooding, endangering crops and livelihoods throughout the region, according to the recently released 2014 National Climate Assessment.

We don’t know, Severinghaus said, “where the natural system will take control and the whole system will shift without us being able to know anything about it.”

Severinghaus emphasized that while the Earth can swing between climate states and even contribute to its own warming, the human element is at the heart of the current abrupt climate change.

“The most important part is that humans are putting [carbon dioxide] into the atmosphere,” he said, “And that’s causing global temperatures to rise.”

CLIMATE SCIENTISTS CAPTURE THE PAST TO FORECAST FUTURE CHANGE

NASA Thwaites Glacier in West Antarctica. Ice is on the move and scientists are concerned about the potential collapse of the ice sheet.
Thwaites Glacier in West Antarctica. Ice is on the move and scientists are concerned about the potential collapse of the ice sheet. (NASA photo)

By Bryce Gray, Katherine Dempsey and Sarah Kramer
Dec 03, 2014

You might want to think of climate researchers as arson investigators.

That’s the comparison made by Penn State climate scientist Richard Alley at the Comer Abrupt Climate Change Conference this fall in southwestern Wisconsin. 

“You would very much want your arson investigator to know what a natural fire looks like, because if you’re going to accuse someone of starting a fire, you better know that nature didn’t do it,” said Alley. “We as climate historians learn what nature has done so that we can tell if what’s going on now is natural.”

Scientists who are piecing together the potential impact of Earth’s current climate crisis keep looking back – thousands and even millions of years into the past.

That’s because understanding where human-driven climate change is headed first requires developing that intimate knowledge of the factors that have influenced climate throughout Earth’s history.

Alley and other top climate researchers from across the country presented their latest findings at the Comer Abrupt Climate Change Conference in southwestern Wisconsin this fall.

Beyond determining the extent to which “our fingerprint” is affecting major processes that regulate global climate, Alley said that looking at historical precedents also provides a glimpse of what might be in store as fossil fuel use pushes concentrations of carbon dioxide to levels not seen in the past 10 to 15 million years.

“By helping to understand the patterns of climate change in the past, we learn the mechanisms, we learn the patterns, and so we help project what will happen in the future and how our actions could affect that.”

Scientists at the conference brought clues from research findings in Greenland, the Arctic, Mongolia, Bhutan and other places around the globe where they measured glacial earthquakes, cored ice for ancient air bubbles, mapped the contraction of lakes and collected rocks hit by cosmic rays as a time machine to document past warming and cooling.

Medill photo The late Gary Comer funded an innovative climate change research program (l to r) that Penn State geoscientist Richard Alley, University of Maine glaciologist George Denton and Columbia University geochemist Wallace Broecker helped coordinate through fellowships at 31 institutions. Continuing funding backs inventive young researchers to fill gaps in the science.
Medill photo
The late Gary Comer funded an innovative climate change research program (l to r) that Penn State geoscientist Richard Alley, University of Maine glaciologist George Denton and Columbia University geochemist Wallace Broecker helped coordinate through fellowships at 31 institutions. Continuing funding backs inventive young researchers to fill gaps in the science.

Geochemist Wallace Broecker, of Columbia University, peered back 50 million years at a time when the land mass of India was on the move and collided into Asia. “That changed the course of the Earth’s environment,” he said. “The collision put the Earth on a new course and the main importance of that course is that it cooled the earth.” 

One lesson from the paleoclimate research is clear: As climate changes, a corresponding shift of the thermal equator has major consequences for human populations.

The thermal equator in turn impacts precipitation. “The rain belts could shift south,” said climate researcher Jeffrey Severinghaus of the University of California, San Diego. “And then you have a billion people in Asia who depend, for their livelihood, on the monsoon, not being able to grow their crops.”

The thermal equator is a band of high temperatures encircling the Earth near the geographic Equator. The geographic boundary never changes but the thermal equator can shift in tandem with global changes. Climatic shifts in the North Atlantic, for instance, typically precede those in the Southern Hemisphere, Severinghaus said. 

Under natural circumstances, these events can occur more than a thousand years before worldwide warming sets in, but their effects are drastic. Now, human-triggered climate change threatens to make these patterns more severe.

Previously, the cooling and warming of the hemispheres represented shifts within stable modes of global climate patterns, according to Severinghaus. However, the excess carbon dioxide associated with human-driven climate change could shift the Earth into an entirely new mode – spelling trouble for human population centers, he said.

Jennifer Draper/MEDILL Glaciologist Richard Alley, among the scientists researching melting glaciers in West Antarctica, compared glacial architecture to Gothic cathedrals with flying buttresses. Rocky fjord walls produce friction and provide strong the buttresses in East Antarctica. But West Antarctica has few buttresses and ocean water flowing under the ice shelves and melting the underbelly of the ice at places such as Thwaites Glacier.
Jennifer Draper/MEDILL
Glaciologist Richard Alley, among the scientists researching melting glaciers in West Antarctica, compared glacial architecture to Gothic cathedrals with flying buttresses. Rocky fjord walls produce friction and provide strong the buttresses in East Antarctica. But West Antarctica has few buttresses and ocean water flowing under the ice shelves and melting the underbelly of the ice at places such as Thwaites Glacier.

Severinghaus also revealed troubling evidence that carbon dioxide levels can rise rapidly, rather than the gradual increase previously thought to occur, due to a positive feedback loop from the soil of the Earth that causes rapid jumps in atmospheric CO2.

Carbon dioxide levels associated with fossil fuel emissions already have risen more than 33 percent during the Industrial Age compared to the previous 800,000 years.
And the levels are acting like a thermostat increasing global temperatures. 
  
The research of glacial expert Brenda Hall showed similar shifts in thinking regarding paleoclimate patterns that offer a clearer understanding of where climate could be headed now.

Hall’s work in the Tierra del Fuego determined that glaciers retreated quickly at the end of the last major ice age that reached its maximum 20,000 years ago. Entire ice sheets collapsed in less than 1,000 years, according to Hall – a mere blink of an eye in geologic time. Over the last two centuries, Hall said, we’ve seen a similar retreat, but with different causes. 

“One was a big, end-of-the-ice-age warming,” she said, “the other is warming over the last century – some of which almost certainly is natural warming and some of which is human-induced.”

Scientists are also using clues from old shorelines to observe past wet and dry periods over thousands of years so they can tie these periods to climate changes.

Nevada State Climatologist Douglas P. Boyle studies past shorelines at closed boundary lakes such as Nevada’s Walker Lake, which are particularly sensitive to fluxes in climate. His team produces lake-level simulations using hydrologic and atmospheric models and historic data. 

At the Comer Conference, he showed scientists how rising levels signify cooling and falling lake levels signify warming. His preliminary field findings resulted from research conducted with others at the University of Nevada, Reno, where he is an associate professor of geography.

Medill photo Pioneering climate scientist Wallace Broecker, of Columbia University, peered back 50 million years at a time when the land mass of India was on the move and collided into Asia. "That changed the course of the Earth's environment," he said.
Medill photo
Pioneering climate scientist Wallace Broecker, of Columbia University, peered back 50 million years at a time when the land mass of India was on the move and collided into Asia. “That changed the course of the Earth’s environment,” he said.

“We can try to figure out how those climates existed and why they existed and how the earth responded to those climates to give us just a better understanding of climate change, why it happens and what are the impacts,” Boyle said.

One period of focus is the Medieval Climatic Anomaly, a heat wave that struck the Great Basin of the U.S. with two “megadroughts.” One of these megadroughts spanned 240 years, 850 to 1,090 A.D., and the other one spanned at least 180 years – 1140 to 1320 A.D. Furthering knowledge of megadroughts will be pivotal in regions expected to contend with drier, warmer conditions wrought by global warming, Boyle said.

Meanwhile, seismologist Meredith Nettles of Columbia University discussed glacial calving – the process of ice breaking off a glacier – and how low tides might be linked to the collapse of ice sheets that send icebergs the size of Central Park crashing into the ocean.

She presented data from observations at Greenland’s Helheim Glacier, linking tides and the occurrence of earthquakes, presumably triggered by the ice breaking. A low tide corresponded to more earthquakes. The glacier stretches out more with low tide and stretching any material makes it break, Nettles explained. Calving models indicate that breaking through the ice is needed for an iceberg to separate.

NASA Broecker discovered the global ocean conveyor belt and how it helps regulate climate worldwide.
NASA
Broecker discovered the global ocean conveyor belt and how it helps regulate climate worldwide.

Taken as a whole, these and other findings from across the globe paint a grim picture of the climate-related challenges facing our warming planet. U.N. climate delegates meeting in Lima, Peru, this month agreed on the draft of a deal to reduce fossil fuel emissions and stop global warming at or near 2 degrees Celsius (3.6 degrees Fahrenheit), the tipping point for widespread melting ice and sea level rise. Temperatures have already risen nearly 1 degree C.

But where some see daunting obstacles, Alley sees a future brimming with opportunities for society to reinvent itself and build a more robust economy, driven by eco-friendly alternative energies.

“Across a huge amount of scholarship, there’s strong agreement that starting now to deal with fossil fuels, to reduce them and switch to other things, makes us better off,” Alley said, emphasizing that such a shift would simultaneously rid the atmosphere of harmful pollutants while also stimulating job creation.

“This is not about losing money – this is about gaining money,” Alley said.

Katherine Dempsey/MEDILL Climate scientists at the Comer Conference gathered to present the latest research from around the world.
Katherine Dempsey/MEDILL
Climate scientists at the Comer Conference gathered to present the latest research from around the world.

Moreover, Alley believes that human beings find themselves at an exciting crossroads – one where we are able to “get off the treadmill” of dependency on convenient but finite energy sources.

“We’ve always been hunter-gatherers of energy, looking for the next thing and then over-hunting it, over-gathering it, and then looking for the next thing,” Alley said. “For the first time in human history we actually can see a way to build something that will power everyone essentially forever.”

 

Alley, Broecker and University of Maine glaciologist George Denton help organize the conference hosted by the Comer Family Foundation and philanthropist Gary Comer’s children Stephanie and Guy Comer.

 

Medill photo Jeffrey Severinghaus joins of the band at the picnic following the Comer Conference. Several scientists make music at the party.
Medill photo
Jeffrey Severinghaus joins of the band at the picnic following the Comer Conference. Several scientists make music at the party.

They help coordinate the foundation’s continuing climate change research program that backs innovative young researchers with Comer funding, a continuing legacy to Gary Comer who died of prostate cancer in 2006.

TIME MACHINE: OLDEST ICE CORES NOW TAKE US BACK A MILLION YEARS

TIME MACHINE: OLDEST ICE CORES NOW TAKE US BACK A MILLION YEARS

[jwplayer player=”1″ mediaid=”381″]

by Bryce Gray
Dec 09, 2014

Take a deep breath – and pretend it’s 800,000 years ago. That ancient air you are breathing is pretty much the same as the stuff you’re inhaling at this moment. Except there’s a lot less carbon dioxide in it.

We know because we’ve recovered that ancient air.

Graphic courtesy of John Higgins Researchers obtained million-year-old ice cores from the area where the ice sheet is uplifted by contact with the Allan Hills, making old ice much easier to extract. “We like to call it ‘getting old ice on the cheap,’" says Princeton geochemist John Higgins. Click on graphic to enlarge.
Graphic courtesy of John Higgins
Researchers obtained million-year-old ice cores from the area where the ice sheet is uplifted by contact with the Allan Hills, making old ice much easier to extract. “We like to call it ‘getting old ice on the cheap,’” says Princeton geochemist John Higgins. Click on graphic to enlarge.

With atmospheric records faithfully preserved in air bubbles trapped in glacial ice, ice core drillings are among the most coveted tools for scientists seeking to capture the climate record – and the CO2 levels linked to temperature rise and fall.

But the record just got a lot older.

Geochemist John Higgins of Princeton University unearthed the oldest relic ice in a million-year-old sample retrieved from the Allan Hills of Antarctica in 2010 and 2011. 

“It predates the oldest continuous atmospheric records by about 200,000 years,” Higgins said at the Comer Abrupt Climate Change Conference, where he presented analysis of his findings this fall.

Despite the superlative age of the ice, Higgins said the sample provides more of a “snapshot” of climatic conditions, though it doesn’t capture an uninterrupted sequence going back a full million years.

“I would call them snapshots of what the atmosphere looked like at 1 million years ago,” Higgins said. “The most desirable thing would be to have a continuous record that went from 800,000 back to 1 million, but because of the nature of the type of ice that we’re looking at, it’s very unlikely that we’ll find these beautifully continuous – I call them layer cake – sequences.”

The time machine of the ice cores suggests that, over warm spells between the ice ages during the past 800,000 years, carbon dioxide levels never rose above about 300 parts per million – until very recently. CO2 levels linked to human fossil fuel emissions are currently at about 400 ppm and rising.

Overall, the oldest ice fits the atmospheric CO2 relationships established across the past 800,000 years.

“It suggests the style of variations we have seen over the last 800,000 years indeed carried back to 1 million years,” Higgins said.

“The interesting new twist is that we do place new constraints on how high carbon dioxide might’ve gotten during interglacial warm periods prior to 800,000 years,” said Higgins.

“Carbon dioxide is definitely higher in the interglacials 1 million years ago than it was from 400,000 to 800,000 years ago. That’s probably the most robust conclusion,” he said. But even the highest levels of the CO2 range he’s researched so far doesn’t exceed 300 parts per million, according to the data he presented.

Higgins said the find of million-year-old ice was made more extraordinary since the core was retrieved from the relatively shallow depth of 130 meters in a spot where ice is pushed upward by the landmass of the Allan Hills. He said that the million-year-old snapshot demonstrates the value of targeting similar ice cores as a cost-effective alternative to deeper excavation efforts, which can delve thousands of meters below the surface.

“We like to call it ‘getting old ice on the cheap’ and the fact that it has been successful, to me, begs the fact that we should be trying to pursue this more,” said Higgins, noting that deeper ice core operations still make invaluable contributions to the field.

Higgins believes that using both methods to extend ice core climate records to the warmer time period of 1.5 to 2 million years ago would be instrumental in developing a better understanding of the carbon cycle’s “central role” in regulating earth’s climate.

“There are lots of questions about how high was the carbon dioxide when it was this much warmer,” Higgins said. “It’s a way to try to look at getting some sort of sense for what the response of changes in atmospheric carbon dioxide are or what effects the changes in atmospheric carbon dioxide are going to have on the climate system.”

ANCIENT SHORELINES MAP LAKE LEVELS TO HELP PREDICT FUTURE DROUGHTS

ANCIENT SHORELINES MAP LAKE LEVELS TO HELP PREDICT FUTURE DROUGHTS

Courtesy of Douglas P. Boyle Nevada State Climatologist Douglas P. Boyle and undergraduates in his Mountain Geography class at the University of Nevada visited the upper West Walker River in fall 2013. The tree stumps they are examining provide evidence that the Medieval Climatic Anomaly struck the Great Basin with warmer temperatures and drought hundreds of years ago.
Courtesy of Douglas P. Boyle
Nevada State Climatologist Douglas P. Boyle and undergraduates in his Mountain Geography class at the University of Nevada visited the upper West Walker River in fall 2013. The tree stumps they are examining provide evidence that the Medieval Climatic Anomaly struck the Great Basin with warmer temperatures and drought hundreds of years ago.

By Katherine Dempsey
Nov 13, 2014

Ancient shorelines in the Great Basin of the western United States reveal clues to severe ancient droughts and that could help us better predict climate change for the future.

Scientists in the U.S. and elsewhere across the globe are trying to use lake clues signifying wet and dry periods over thousands of years in order to tie these periods to past climate changes. A warming planet is expected to cause increased dryness and drought in many areas, including the western U.S.

Nevada State Climatologist Douglas P. Boyle studies past shorelines at terminal lakes (lakes with evaporation as the only outlet) such as Nevada’s Walker Lake and other closed lakes because they so sensitive to climate fluctuations. His research group creates lake-level simulations using hydrologic and atmospheric models and historic data in order to gain insight about previous climate.

Walker Lake levels are dropping as the drought in California and Nevada persists, said Boyle, an associate professor in the geography department at the University of Nevada, Reno. Without sufficient water upstream for crops, farmers are now pumping groundwater, he said, but it’s uncertain how long the drought will persist, and groundwater is a finite source.

At the Comer Abrupt Climate Change Conference held in southwestern Wisconsin this fall, he gathered with other top climate change scientists and showed them how rising and falling lake levels depict climate change. He presented preliminary results from research conducted with his doctoral advisee Benjamin Hatchett and others at the University of Nevada.

“We can try to figure out how those climates existed and why they existed and how the earth responded to those climates to give us just a better understanding of climate change, why it happens and what are the impacts,” Boyle said.

Low shorelines signify dry climate and high shorelines signify wet climate. Boyle’s team created corresponding “wet” and “dry” simulations of Walker Lake depths using the average monthly precipitations and average monthly temperatures from the 20 wettest and 20 driest water years from 1920 to 2011. Their model of the Walker River Basin produced “runoff” based on the synthetic dry and wet climates, resulting in both dry and wet simulated lake levels.

Boyle’s group has mapped their wet and dry simulations against the most recent “highstand” of Walker Lake in the late 1800s and its shoreline during the Medieval Climatic Anomaly, which struck the Great Basin of the U.S. with two “megadroughts.” One of the megadroughts spanned 240 years, 850 to 1,090 A.D., and the other spanned at least 180 years – 1140 to 1320 A.D. Throughout these times, annual precipitation was at least 40 percent less than precipitation in our present-day climate, according to early results from the Nevada State Climate Office at the University of Nevada, Reno.

Courtesy of Douglas P. Boyle Simulations of Walker Lake’s levels mapped against the 2014 elevation, its most recent highstand in the 1800s and the Medieval lowstand. The control simulation signifies where the lake level would be without agricultural activities consuming so much water upstream.Click on image to enlarge.
Courtesy of Douglas P. Boyle
Simulations of Walker Lake’s levels mapped against the 2014 elevation, its most recent highstand in the 1800s and the Medieval lowstand. The control simulation signifies where the lake level would be without agricultural activities consuming so much water upstream.Click on image to enlarge.

Other researchers have used datable objects like shells, wood and trees to find the historical locations of the past shorelines. Boyle said closed-basin lakes are “extremely sensitive” to varying climate and provide a barometer of what the climate was like.

Walker Lake’s elevation above sea level is 3,914 feet this year compared to more than 4,100 for the most recent highstand. For consistency, Boyle’s team documents shoreline elevations above sea level rather than water depths that can vary from place to place in a lake. The current level is only about three feet higher than the level of a “dry simulation” run after the Comer conference. The “wet simulation” was 344 feet higher than the 2014 level. The 2014 level is 52 feet lower than the MCA lowstand during severe and prolonged drought periods.

Boyle noted, however, that Walker Lake’s 2014 elevation is due to agricultural water consumption upstream rather than climate. If farming weren’t a factor, the lake level would likely be nearly 200 feet higher at present, making it 147 feet higher than the MCA low, according to new simulations run after the Comer Conference.

Boyle’s group also tried to figure out what made the climate change, examining the atmosphere of a subset of the 20 wet and dry water years. They noticed high pressure over the West Coast during drought periods but low pressure during wet periods. High pressure blocked the storm track, meaning it couldn’t carry storms to Nevada and California. Conversely, low pressure let the storms pass over the western Great Basin.

High pressure pushing the storm track to the Pacific Northwest during the last three winters has created the drought, Boyle said.

Now, Boyle’s team needs to figure out what created the atmospheric behaviors – the high pressure and low pressure – that accompanied the dry and wet climates from the subset, he said. Plus, they need to learn more about the link between those behaviors and “paleo periods” of wetness and dryness corresponding to 13,000-14,000 years ago and the MCA, respectively.

“We’re trying to understand from the historic period where we do know what the atmosphere was like for wet years and dry years and try and better understand how the atmosphere might have been behaving in the paleo wet and paleo dry periods,” Boyle said.

Learning why climate changed during those paleo periods could give us more information about how the planet might act in response to global warming driven by human fossil fuel use, Boyle said.

“We have an incredible amount of CO2 and other greenhouse gases that have been put into the atmosphere,” Boyle said. “We’re still learning how the earth is responding to that.”

Boyle is also working with climate scientist Sean Birkel to create a climate model of China’s Tarim Basin. They are trying to pinpoint the climate conditions that would allow lake Lop Nor to display a highstand of about 2,625 feet, which was the level of the shoreline at around 1850. Lop Nor has been dry since around 1950.

NASA Earth Observatory Boyle and Sean Birkel of the University of Maine are working to model climate change in China's desert-filled Tarim Basin, seen here via satellite. This dust bowl stretches across nearly 260,000 square kilometers, hemmed in by mountains and the Tibet Plateau.
NASA Earth Observatory
Boyle and Sean Birkel of the University of Maine are working to model climate change in China’s desert-filled Tarim Basin, seen here via satellite. This dust bowl stretches across nearly 260,000 square kilometers, hemmed in by mountains and the Tibet Plateau.

At the Comer Conference, Birkel spoke about the difficulty of trying to simulate Lop Nor’s level. These problems stem from the Tarim Basin’s large size – about 1,200 miles long. Two key atmospheric circulation systems control precipitation and influence climate in the region: monsoon-driven precipitation in the south and westerly wind-driven precipitation in the north. Factoring in both of these systems complicates modeling.

 

Birkel is helping to develop Climate Adaptation and Sustainility (CLAS) software for the University of Maine’s Climate Change Institute.

Yonaton Goldsmith, a Ph.D. student in geochemistry at Lamont-Doherty Earth Observatory at Columbia University, studied China’s Dali Lake, comparing lake records with Chinese cave records to find out how the intensity of the East Asian summer monsoon varied throughout the last 16,000 years. The lake is located on the edge of the monsoon’s reach. 

Three types of evidence help determine lake levels – lake sediments containing shells, beach ridges, and alluvial deposits. “If we find lake sediments that have shells in them, we can say that the lake was higher,” he told scientists at the Comer Conference. Beach ridges signify the lake elevation, and alluvial deposits show lower lake level.

CLIMATE CHANGE MAY BE STALLING OVERDUE ICE AGE

CLIMATE CHANGE MAY BE STALLING OVERDUE ICE AGE

Courtesy of Brenda Hall The Kalv Glacier in Cordillera Darwin at Bahia Pia, Chile, one of the research bases for Hall's team. The Tierra del Fuego glaciers, like this one, are rapidly disappearing due to human-caused warming.
Courtesy of Brenda Hall
The Kalv Glacier in Cordillera Darwin at Bahia Pia, Chile, one of the research bases for Hall’s team. The Tierra del Fuego glaciers, like this one, are rapidly disappearing due to human-caused warming.

by Sarah Kramer
Nov 28, 2014

Despite warming temperatures worldwide, scientists are exploring Earth’s ancient cold snaps. Researching how past ice ages ended can reveal clues about our planet’s future. 

Some of the evidence suggests that we might be overdue for an ice age, in fact, according to glaciologist Brenda Hall of the University of Maine. 

Hall’s research shows that ancient glaciers might have retreated rapidly as part of Earth’s natural pattern of ice ages. The Earth’s previous warming periods and the current one can be traced to a global rise in air temperature—with one key difference. 

“One was a big, end-of-the-ice-age warming,” said Hall, whose team conducted the research in the Tierra del Fuego, Chile. “The other is warming over the last century, some of which is natural warming and some of which is human-induced.” 

Most of this human-induced warming is related to carbon dioxide, a greenhouse gas that traps heat in the atmosphere. Gasoline, coal and natural gas are all carbon-based and burning them for fuel emits carbon dioxide. 

Things can change fast. Ice sheets in the Andes melted down to modern glaciers “in less than a thousand years, which, from a geologic point of view, is really fast,” Hall said. Hall, an associate professor at the University of Maine, presented her research at the Comer Conference on Abrupt Climate Change in Wisconsin earlier this October.

Her research set out to discover how and why ice ages ended in the Southern Hemisphere, using glaciers in the Cordillera Darwin range of the Andes at the tip of South America. These high mountains still host remnants of a massive ice sheet from the last ice age. The research used geological features and peat bog cores to date the start of a warming period that led to the end of last the ice age 18,000 years ago. 

The ice melted much faster, as it turns out, than scientists had thought. According to Hall, the ice sheet was so extensive at end of the ice age that its mass became unsustainable. As the ice became unstable and air temperature began warming, the glaciers made a rapid retreat. 

Medill photo Glaciologist Brenda Hall shows how we may be overdue for an ice age.
Medill photo
Glaciologist Brenda Hall shows how we may be overdue for an ice age.

While scientists know that the Earth goes through periods of warming and cooling, and that the human contribution to climate change is now causing more dramatic warming, not everything is clear. Hall said scientists are still trying to understand the Earth’s “natural climate variability” in order to better predict the effects of human-driven climate change. 

One such effect may be that human-caused warming is delaying an overdue ice age. Hall’s research dated the beginning of the end of the last ice age to 18,000 years ago, but “interglacials” — the periods of relative warmth between glacial periods of an ice age—usually last only 15,000 years, meaning we’re overdue for another cold snap.

Hall emphasized that this hypothesis hasn’t been proven but it is one possible effect of humanity’s massive release of carbon dioxide into the atmosphere over the last two centuries. 

“Eventually, the Earth will do what the Earth wants to do,” Hall said. “If it’s scheduled to go into an ice age it eventually will. But it might be delayed” due to warming temperatures. 

Scientists don’t really know why the entire planet enters or leaves ice ages at the same time, despite seemingly opposing climate conditions in the northern and southern hemispheres. This opposition of the poles means that when conditions in one hemisphere seems ideal for an ice age, conditions in the other hemisphere’s may be unfavorable to a global freeze. However, the planet still seems to phase in an out of ice ages as a whole, not in hemispheric pieces. 

“That is the big ice age mystery,” Hall said. “We just know that it went from a full glacier to no glacier almost overnight, geologically speaking.”

Hall is looking at the current rapid melting of the West Antarctic ice sheet that is contributing to rising sea levels.


Medill School Of Journalism, Media, Integrated Marketing Communications
1845 Sheridan Road, Evanston, IL 60208-2101 © 2020 Northwestern University