Category Archives: sea level change

Ice Island Calves off Petermann Glacier

Ice Island Calves off Petermann Glacier : Natural Hazards.

Ice Island Calves off Petermann Glacier

acquired July 20, 2011download large image (716 KB, JPEG, 2000×2600)
acquired July 20, 2011download GeoTIFF file (7 MB, TIFF, 2000×2600)
acquired July 20, 2011download Google Earth file (KMZ)

In August 2010, the Petermann Glacier along the northwestern coast of Greenland calved an ice island roughly four times the size of Manhattan. Nearly a year later, on July 20, 2011, a piece of that ice island—named Petermann Ice Island-A (PII-A) and about the same size as Manhattan—was still visible to the Moderate Resolution Imaging Spectroradiometer(MODIS) on NASA’s Terra satellite.

The Canadian Ice Service (CIS) tracked the ice island as it drifted through the Labrador Sea. On July 8, 2011, the CIS reported that the PII-A was approximately 55 square kilometers (21 square miles), and was continuing to lose surface area through calving and melting. On July 20, MODIS observed PII-A slightly south of where it had been a month earlier.

On July 21, 2011, MSNBC reported that PII-A was slowly drifting toward Newfoundland. The glacier was not likely to reach land; its base would probably become grounded on the sea floor off the coast. The ice chunk did, however, pose a potential hazard for shipping lanes and offshore oil rigs.

  1. References

  2. Canadian Ice Service (2011, July 8). Petermann Ice Island Updates. Accessed July 22, 2011.
  3. MSNBC. (2011, July 21). Massive ice island drifts toward Canada. Accessed July 22, 2011.

NASA image courtesy Jeff Schmaltz, MODIS Rapid Response, NASA Goddard Space Flight Center. Caption by Michon Scott.

Instrument: 
Terra – MODIS

Long-lost Lake Agassiz offers clues to climate change

Long-lost Lake Agassiz offers clues to climate change.

ScienceDaily (Oct. 5, 2011) — What caused water levels to drop in an immense yet long-vanished lake? Research by a University of Cincinnati geologist suggests that conditions 12,000 years ago encouraged evaporation.

Not long ago, geologically speaking, a now-vanished lake covered a huge expanse of today’s Canadian prairie. As big as Hudson Bay, the lake was fed by melting glaciers as they receded at the end of the last ice age. At its largest, Glacial Lake Agassiz, as it is known, covered most of the Canadian province of Manitoba, plus a good part of western Ontario. A southern arm straddled the Minnesota-North Dakota border.

Not far from the ancient shore of Lake Agassiz, University of Cincinnati Professor of Geology Thomas Lowell will present a paper about the lake to the Geological Society of America annual meeting in Minneapolis. Lowell’s paper is one of 14 to be presented Oct. 10 in a session titled: “Glacial Lake Agassiz — Its History and Influence on North America and on Global Systems: In Honor of James T. Teller.”

Although Lake Agassiz is gone, questions about its origin and disappearance remain. Answers to those questions may provide clues to our future climate. One question involves Lake Agassiz’ role in a thousand-year cold snap known as the Younger Dryas.

As the last ice age ended, thousands of years of warming temperatures were interrupted by an abrupt shift to cold. Tundra conditions expanded southward, to cover the land exposed as the forests retreated. This colder climate is marked in the fossil record by a flowering plant known as Dryas, which gives the period its name.

“My work focuses on abrupt or rapid climate change,” Lowell said. “The Younger Dryas offers an opportunity to study such change. The climate then went from warming to cooling very rapidly, in less than 30 years or so.”

Scientists noted that the Younger Dryas cold spell seemed to coincide with lower water levels in Lake Agassiz. Had the lake drained? And, if so, had the fresh water of the lake caused this climate change by disrupting ocean currents? This is the view of many scientists, Lowell said.

Lowell investigated a long-standing mystery involving Lake Agassiz — a significant drop in water level known as the Moorhead Low. It has long been believed that the Moorehead Low when water drained from Lake Agassiz through a new drainage pathway. Could this drainage have flowed through the St. Lawrence Seaway into the North Atlantic Ocean?

“The most common hypothesis for catastrophic lowering is a change in drainage pathways,” Lowell said.

The problem is, better dating of lake levels and associated organic materials do not support a rapid outflow at the right time.

“An alternative explanation is needed,” he said.

Lowell’s research shows that, although water levels did drop, the surface area of the lake increased more than seven-fold at the same time. His research suggests that the lower water levels were caused by increased evaporation, not outflow. While the melting glacier produced a lot of water, Lowell notes that the Moorhead Low was roughly contemporaneous with the Younger Dryas cold interval, when the atmosphere was drier and there was increased solar radiation.

“The dry air would reduce rainfall and enhance evaporation,” Lowell said. “The cold would reduce meltwater production, and shortwave radiation would enhance evaporation when the lake was not frozen and sublimation when the lake was ice-covered.”

Further research will attempt a clearer picture of this ancient episode, but researchers will have to incorporate various factors including humidity, yearly duration of lake ice, annual temperature, and a better understanding of how and where meltwater flowed from the receding glaciers.

Lowell’s efforts to understand changes in ancient climates have taken him from Alaska to Peru, throughout northern Canada and Greenland.

In Greenland, Lowell and a team of graduate students pulled cores of sediment from lakes that are still ice-covered for most of the year. Buried in those sediments are clues to long-ago climate.

“We look at the mineralogy of the sediments,” Lowell said, “and also the chironomids. They’re a type of midge and they’re very temperature sensitive. The exact species and the abundance of midges in our cores can help pinpoint temperature when these sediments were deposited.”

Lowell’s research was initially funded by the Comer Foundation. In recent years, the National Science Foundation has provided funding for this work.

When the Geological Society of America meets this year the University of Cincinnati will be well represented, with more than two dozen papers and presentations. Topics range from ice-age climate to the health effects of corrosion in drinking water pipes.

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Europe's oceans changing at unprecedented rate

Europe’s oceans changing at unprecedented rate: report | Reuters.

LONDON | Tue Sep 13, 2011 3:26pm EDT

(Reuters) – Europe’s seas are changing at an unprecedented rate as ice sheets melt, temperatures rise and marine life migrates due to climate change, a report by the Climate Change and European Marine Ecosystem Research (CLAMER) project warned.

Scientists examined a mass of EU-funded research on the impacts of climate change on Europe’s marine environment and identified the gaps and priorities for future work.

“Change has been clearly visible and is much more rapid than we thought was possible,” Carlo Heip, chair of the CLAMER project and lead author of the report, told Reuters on Tuesday.

Over the past 25 years, sea water temperatures have increased as Arctic sea ice has melted. The combination of rising sea-levels and increased winds has contributed to the erosion of 15 percent of European coasts, the report said.

Warming has speeded up in the past 25 years at around 10 times faster than the average rate of increase in the 20th century, it added.

From 1986 to 2006, sea surface temperature rises for European waters were three to six times higher than the global average.

“Scenario simulations suggest that by the end of the 21st century, the temperature of the Baltic Sea may have increased by 2 to 4 degrees centigrade, the North Sea by 1.7 degrees, and the Bay of Biscay by 1.5 to 5 degrees,” the report said.

Melting ice sheets and glaciers add more uncertainty. Current estimates for 2100 suggest European sea levels could rise 60 cms and up to 1.9 meters at some British coasts.

Sea level rise threatens populations in all low-lying areas of Europe, but countries such as Britain, France and the Netherlands could be less vulnerable because they are rich enough to adopt coastal protection measures.

Changes in the marine food chain have also occurred as organisms have migrated to the Atlantic from the Pacific via seasonal ice-free passages through the Arctic.

While some species can thrive in other oceans, any major upheaval to the marine ecosystem could have devastating effects, the report said.

CLAMER also found that some bacteria strains were becoming more prevalent and could be a potential threat to human health. For example, cholera strains have increased in the North Sea over the past 50 years, perhaps due to temperature change.

Among its many recommendations, CLAMER urged more study of seal-level changes due to ice sheets breaking up or melting, coastal erosion, temperature changes, ocean acidification, marine ecosystems and circulation changes.

“The main message is we need to keep our fingers on the pulse,” said Heip.

The full report is available at: www.clamer.eu/

(Editing by Janet Lawrence)

Arctic Ice Loss at near-record levels & Several Other Reuters Updates

 

 

 

 

 

 

 

 

 

World Atlas ice loss claim exaggerated: scientists | Reuters.

LONDON | Mon Sep 19, 2011 3:27pm EDT

(Reuters) – The Times Atlas of the World exaggerated the rate of Greenland’s ice loss in its thirteenth edition last week, scientists said on Monday.

The atlas, published by HarperCollins, showed that Greenland lost 15 percent of its ice cover over the past 12 years, based on information from the National Snow and Ice Data Center in Colorado in the United States.

The Greenland ice sheet is the second biggest in the world and significant shrinking could lead to a global rise in sea levels.

“While global warming has played a role in this reduction, it is also as a result of the much more accurate data and in-depth research that is now available,” HarperCollins said on its website on Monday.

However, a number of scientists disputed the claim.

“We believe that the figure of a 15 percent decrease in permanent ice cover since the publication of the previous atlas 12 years (ago) is both incorrect and misleading,” said Poul Christoffersen, glaciologist at the Scott Polar Research Institute (SPRI) at the University of Cambridge.

“We concluded that a sizable portion of the area mapped as ice-free in the Atlas is clearly still ice-covered.”

Other scientists agreed.

“These new maps are ridiculously off base, way exaggerated relative to the reality of rapid change in Greenland,” said Jeffrey S. Kargel, senior research scientist at the University of Arizona.

The Times Atlas suggested the Greenland ice sheet has lost 300,000 square kilometers in the past 12 years, at a rate of 1.5 percent per year.

However, measurements suggest this rate is at least 10 times faster than in reality, added J. Graham Cogley, Professor of Geography at Trent University, Ontario, Canada.

“It could easily be 20 times too fast and might well be 50 times too fast,” he added.

Last year, a U.N. committee of climate scientists came under fire for bungling a forecast of when Himalayan glaciers would thaw.

The panel’s 2007 report, the main guide for governments in fighting climate change, included an incorrect projection that all Himalayan glaciers could vanish by 2035, hundreds of years earlier than scientists’ projections.

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Summer Arctic sea ice melt at or near record

(Reuters) – Arctic sea ice this summer melted to a record low extent or will come a close second, two different research institutes said on Tuesday, confirming a trend which could yield an ice-free summer within a decade.

The five biggest melts in a 32-year satellite record have all happened in the past five years, likely a result of both manmade climate change and natural weather patterns.

One impact of an ice-free summer may be disrupted world weather, with hints already as some scientists blame recent chill winters in Europe and North America on warmer, open Arctic seas diverting polar winds south.

Researchers at the University of Bremen in Germany say that this year has already toppled 2007 after sea ice retreated to a record low on September 8.

The U.S.-based National Snow and Ice Data Center (NSIDC) says this year is number two with the melt season all but over before winter returns to the high Arctic.

“I’m increasingly confident it will remain number two,” said Mark Serreze, head of the NSIDC. But the result may be close enough to declare a tie, he added.

Most important than the record was the trend, said University of Bremen’s Georg Heygsterall, referring to how the years since 2007 had all since bigger summer melts than those before.

A tie would echo the World Meteorological Organization’s view on recent rising global temperatures, after it declared 2010 a tie with 1998 and 2005 for the hottest year since such records began about a century and a half ago.

Bremen and NSIDC use satellites to measure microwave radiation from the ice pack, but with slightly different methods: NSIDC can achieve a sharper image, but Bremen to a higher resolution of 6 kilometers compared with 25 km.

TREND

Researchers agree that summer sea ice is disappearing faster than expected.

“An ‘ice-free’ summer Arctic is rapidly on its way. Most data indicate that the models are underestimating the rate of ice-loss,” said Kim Holmen, research director at the Norwegian Polar Institute.

“That means that we see more rapid change than the model scenarios have suggested. It also means that there are processes out there that influence ice that we have yet to understand.”

The summer ice retreat has already reached levels which were forecast three decades from now in models used in the U.N. climate panel’s flagship report four years ago.

The Intergovernmental Panel on Climate Change (IPCC) used models which forecasted an ice-free summer at the end of this century.

But that could happen as early as 2013, according to one of the most aggressive estimates. Other experts predict an ice-free Arctic Ocean in summer anywhere from 2020-2050.

“I still see a high likelihood of a near ice-free Arctic Ocean during summer around 2016, plus or minus three years,” said Wieslaw Maslowski at the California-based Naval Postgraduate School.

More difficult to measure than area is ice thickness, which is also diminishing, most scientists agree.

Researchers at the University of Washington in Seattle calculated ice volume, combining area and thickness, reached a record low last year and would do so again this year.

(Reporting by Gerard Wynn)

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More on Sea-Ice loss:

Thu Sep 15, 2011 3:49pm EDT

<span class="articleLocation”>(Reuters) – Sea ice on the Arctic Ocean shrank to its second-smallest extent since modern records began, in keeping with a long-term trend, the U.S. National Snow and Ice Data Center reported on Thursday.

The annual sea ice minimum was reached on September 9, the center said on its website here in a preliminary finding.

“Changing winds could still push ice flows together reducing ice extend further,” the researchers said. A full analysis will be available in October, when monthly data are available for all of September, which is usually the month when the annual minimum is reached.

Arctic Sea ice is an important sign of a changing climate, and what happens in the Arctic has a major influence on global weather patterns.

At its apparent minimum, sea ice around the North Pole covered 1.67 million square miles (4.33 million square km). That measurement is 61,800 square miles (160,000 square km) above the all-time record low reached in 2007, the center said.

However, it is far below the average minimum for the period 1979 through 2000, according to NSIDC. The satellite record began in 1979.

These figures differ from those reported by the University of Bremen in German, which issued a statement that the Arctic ice reached a record low minimum on September 8.

PATCHES OF WATER AMID THE ICE

Both the University of Bremen and NSIDC use microwave sensors to observe Arctic ice, but these sensors are on different satellites. The Bremen report uses images with higher spatial resolution, according to Walter Meier of NSIDC.

“They can see in more detail, they can see these little patches of water, whereas we see these areas as just ice covered,” Meier said by telephone. He said there can be higher potential for error with these high-resolution images, though there is no evidence of error in this case.

NSIDC’s records go back to 1979; the records used by Bremen go back to 2003. Both indicate the last five years were the least icy in the Arctic sea ice satellite record.

It’s not surprising that this year has not eclipsed the record year of 2007, Meier said.

That year was “a perfect storm” of ice-melting conditions in the Arctic, he said: warmer and sunnier than usual, with extremely warm ocean water and winds all acting in concert.

The fact that 2011 has seen the second-lowest ice extent without these extreme conditions shows a change in the character of the ice cover, Meier said.

Back in 2007, the ice was a consolidated mass which melted from the edges. This year, he said, the ice is more dispersed and the area is dominated by seasonal ice cover — less hardy than multi-year ice — which is more prone to melt.

“Now it doesn’t take as extreme of weather conditions to get to the 2007 ballpark,” Meier said.

(Reporting by Deborah Zabarenko in Washington, Editing by Cynthia Osterman)

 

 

Petermann Glacier break-up

BBC News – ‘Gob-smacking’ scale of Petermann Glacier break-up.

These photos of the Petermann Glacier were taken two years apart, in the summer of 2009 (top) and in July 2011 These photos of the Petermann Glacier were taken two years apart, the latest one in July 2011 (top) and in the summer of 2009

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New pictures have revealed the extent to which a huge glacier in northern Greenland has broken up in just two years, claims a glaciologist.

Dr Alun Hubbard of Aberystwyth University said he was “gob-smacked” by the scale of the Petermann Glacier’s break-up since he last visited in 2009.

The glacier is 186 miles (300km) long and 3,280ft (1000m) high – over three times the height of the Eiffel Tower.

Last year, it shed a piece of ice measuring 77 square miles (200 sq km).

Dr Hubbard has been researching the Greenland ice sheet for some years.

His team of researchers and scientists from Aberystwyth and Swansea universities have made several trips to the country.

Located in north west Greenland, the Petermann Glacier accounts for 6% of the area of the Greenland ice sheet, said Dr Hubbard.

Start Quote

It’s like looking into the Grand Canyon full of ice and coming back two years later to find it’s full of water”

Dr Alun Hubbard Aberystwyth University

It terminates as a floating tongue of ice, measuring around 43 miles (70km) long by 12 miles (20km) wide, the largest of its kind in the northern hemisphere.

“Although I knew what to expect in terms of ice loss from satellite imagery, I was still completely unprepared for the gob-smacking scale of the break-up, which rendered me speechless,” said Dr Hubbard.

“It was incredible to see. This glacier is huge, 20km across and 1000m high.

“It’s like looking into the Grand Canyon full of ice and coming back two years later to find it’s full of water.”

He said data recovered from global positioning system (GPS) sensors at the site was being analysed at Aberystwyth.

Cracks and rifts

With support from the US National Science Foundation and the Natural Environment Research Council in the UK, Dr Hubbard travelled by helicopter to the glacier to gather data from time lapse cameras and GPS sensors set up in July and August 2009, with the help of Greenpeace.

The GPS sensors were set in anticipation of a large break-up of ice that eventually occurred by on 3 August, 2010.

Dr Hubbard said this led to the formation of an ice island measuring more than 77 square miles (200 sq km).

He believes the cracks and rifts in what remains of the ice shelf means it is also likely to break up at some point in the near future.

Dr Hubbard visited the Petermann glacier at the end of July, and returns to Aberystwyth on Sunday.

His work is part of a wider project involving researchers from Bristol, Cambridge, Edinburgh, Denmark, Sweden, the Netherlands, Germany and the United States.

Antarctica rising as ice caps melt

Antarctica rising as ice caps melt – environment – 31 July 2011 – New Scientist.

ANTARCTICA is rising like a cheese soufflé: slowly but surely. Lost ice due to climate change and left-over momentum from the end of the last big ice age mean the buoyant continent is heaven-bound.

Donald Argus of NASA’s Jet Propulsion Laboratory in Pasadena, California, and colleagues used 15 years of GPS data to show that parts of the Ellsworth mountains in west Antarctica are rising by around 5 millimetres a year (Geophysical Research Letters, DOI: 10.1029/2011gl048025). Elsewhere on the continent, the rise is slower.

A faster rise has been seen in Greenland, which is thought to be popping up by 4 centimetres a year.

Ongoing climate change could be partly to blame: Antarctica is losing about 200 gigatonnes of ice per year, and for Greenland the figure is 300 gigatonnes. Earth’s continents sit on viscous magma, so the effect of this loss is like taking a load off a dense foam mattress.

But there is another possible contributor. “The Earth has a very long memory,” says Argus. As a result, “there is also a viscous response to ice loss from around 5000 to 10,000 years ago going on”.

Despite this effect, the known ice loss at both poles suggests that embedded in the local rises is a signal of current climate change – researchers just have to tease it out.

Sea level rise more from Antarctica than from Greenland during last interglacial

Sea level rise less from Greenland, more from Antarctica, than expected during last interglacial.

Where did all that extra water come from? Mainly from melting ice sheets on Greenland and Antarctica, and many scientists, including University of Wisconsin-Madison geoscience assistant professor Anders Carlson, have expected that Greenland was the main culprit.

But Carlson’s new results, published July 29 in Science, are challenging that assertion, revealing surprising patterns of melting during the last interglacial period that suggest that Greenland’s ice may be more stable — and Antarctica’s less stable — than many thought.

“The Greenland Ice Sheet is melting faster and faster,” says Carlson, who is also a member of the Center for Climatic Research in the Nelson Institute for Environmental Studies. But despite clear observations of that fact, estimates of just how much the ice will melt and contribute to sea level rise by the end of this century are highly varied, ranging from a few centimeters to meters. “There’s a clear need to understand how it has behaved in the past, and how it has responded to warmer-than-present summers in the past.”

The ice-estimation business is rife with unknown variables and has few known physical constraints, Carlson explains, making ice sheet behavior — where they melt, how much, how quickly — the largest source of uncertainty in predicting sea level rises due to climate change.

His research team sought a way to constrain where ice remained on Greenland during the last interglacial period, around 125,000 years ago, to better define past ice sheet behavior and improve future projections.

The researchers analyzed silt from an ocean-floor core taken from a region off the southern tip of Greenland that receives sediments carried by meltwater streams off the ice sheet. They used different patterns of radiogenic isotopes to identify sources of the sediment, tracing the silt back to one of three “terranes” or regions, each with a distinct geochemical signature. The patterns of sedimentation show which terranes were still glaciated at that time.

“If the land deglaciates, you lose that sediment,” Carlson explains. But to their surprise, they found that all the terranes were still supplying sediment throughout the last interglacial period and thus still had some ice cover.

“The ice definitely retreated to smaller than present extent and definitely raised sea level to higher than present” and continued to melt throughout the warm period, he adds, but the sediment analysis indicates that “the ice sheet seems to be more stable than some of the greater retreat values that people have presented.”

The team used their results to evaluate several existing models of Greenland ice sheet melting during the last interglacial period. The models consistent with the new findings indicate that melting Greenland ice was responsible for a sea level rise of 1.6 to 2.2 meters — at most, roughly half of the minimum four-meter total increase.

Even after accounting for other Arctic ice and the thermal expansion of warmer water, most of the difference must have come from a melting Antarctic ice sheet, Carlson says.

“The implication of our results is that West Antarctica likely was much smaller than it is today,” and responsible for much more of the sea level rise than many scientists have thought, he says. “If West Antarctica collapsed, that means it’s more unstable than we expected, which is quite scary.”

Ultimately, Carlson says he hopes this line of research will improve the representation of ice sheet responses to a warming planet in future Intergovernmental Panel on Climate Change (IPCC) reports. Temperatures during the last interglacial period were similar to those expected by the end of this century, and present-day temps have already reached a point that Greenland’s glaciers are melting.

The Science paper was co-authored by UW-Madison colleagues Elizabeth Colville, Brian Beard, Alberto Reyes, and David Ullman and Oregon State University researchers Robert Hatfield and Joseph Stoner, and supported by UW-Madison and the National Science Foundation.

Too late to turn back Rising oceans?

Rising oceans: Too late to turn the tide?.

If sea levels rose to where they were during the Last Interglacial Period, large parts of the Gulf of Mexico region would be under water (red areas), including half of Florida and several Caribbean islands. (Credit: Illustration by Jeremy Weiss)

ScienceDaily (July 18, 2011) — Thermal expansion of seawater contributed only slightly to rising sea levels compared to melting ice sheets during the Last Interglacial Period, a University of Arizona-led team of researchers has found.

The study combined paleoclimate records with computer simulations of atmosphere-ocean interactions and the team’s co-authored paper is accepted for publication in Geophysical Research Letters.

As the world’s climate becomes warmer due to increased greenhouse gases in the atmosphere, sea levels are expected to rise by up to three feet by the end of this century.

But the question remains: How much of that will be due to ice sheets melting as opposed to the oceans’ 332 billion cubic miles of water increasing in volume as they warm up?

For the study, UA team members analyzed paleoceanic records of global distribution of sea surface temperatures of the warmest 5,000-year period during the Last Interglacial, a warm period that lasted from 130,000 to 120,000 years ago.

The researchers then compared the data to results of computer-based climate models simulating ocean temperatures during a 200-year snapshot as if taken 125,000 years ago and calculating the contributions from thermal expansion of sea water.

The team found that thermal expansion could have contributed no more than 40 centimeters — less than 1.5 feet — to the rising sea levels during that time, which exceeded today’s level up to eight meters or 26 feet.

At the same time, the paleoclimate data revealed average ocean temperatures that were only about 0.7 degrees Celsius, or 1.3 degrees Fahrenheit, above those of today.

“This means that even small amounts of warming may have committed us to more ice sheet melting than we previously thought. The temperature during that time of high sea levels wasn’t that much warmer than it is today,” said Nicholas McKay, a doctoral student at the UA’s department of geosciences and the paper’s lead author.

McKay pointed out that even if ocean levels rose to similar heights as during the Last Interglacial, they would do so at a rate of up to three feet per century.

“Even though the oceans are absorbing a good deal of the total global warming, the atmosphere is warming faster than the oceans,” McKay added. “Moreover, ocean warming is lagging behind the warming of the atmosphere. The melting of large polar ice sheets lags even farther behind.”

“As a result, even if we stopped greenhouse gas emissions right now, the Earth would keep warming, the oceans would keep warming, the ice sheets would keep shrinking, and sea levels would keep rising for a long time,” he explained.

They are absorbing most of that heat, but they lag behind. Especially the large ice sheets are not in equilibrium with global climate,” McKay added. ”

Jonathan Overpeck, co-director of the UA’s Institute of the Environment and a professor with joint appointments in the department of geosciences and atmospheric sciences, said: “This study marks the strongest case yet made that humans — by warming the atmosphere and oceans — are pushing the Earth’s climate toward the threshold where we will likely be committed to four to six or even more meters of sea level rise in coming centuries.”

Overpeck, who is McKay’s doctoral advisor and a co-author of the study, added: “Unless we dramatically curb global warming, we are in for centuries of sea level rise at a rate of up to three feet per century, with the bulk of the water coming from the melting of the great polar ice sheets — both the Greenland and Antarctic Ice Sheets.”

According to the authors, the new results imply that 4.1 to 5.8 meters, or 13.5 to 19 feet, of sea level rise during the Last Interglacial period was derived from the Antarctic Ice Sheet, “reemphasizing the concern that both the Antarctic and Greenland Ice Sheets may be more sensitive to warming temperatures than widely thought.”

“The central question we asked was, ‘What are the warmest 5,000 years we can find for all these records, and what was the corresponding sea level rise during that time?'” McKay said.

Evidence for elevated sea levels is scattered all around the globe, he added. On Barbados and the Bahamas, for example, notches cut by waves into the rock six or more meters above the present shoreline have been dated to being 125,000 years old.

“Based on previous studies, we know that the sea level during the Last Interglacial was up to 8.5 meters higher than today,” McKay explained.

“We already knew that the vast majority came from the melting of the large ice sheets in Greenland and Antarctica, but how much could the expansion of seawater have added to that?”

Given that sea surface temperatures were about 0.7 degrees warmer than today, the team calculated that even if the warmer temperatures reached all the way down to 2,000 meters depth — more than 6,500 feet, which is highly unlikely — expansion would have accounted for no more than 40 centimeters, less than a foot and a half.

“That means almost all of the substantial sea level rise in the Last Interglacial must have come from the large ice sheets, with only a small contribution from melted mountain glaciers and small ice caps,” McKay said.

According to co-author Bette Otto-Bliesner, senior scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., getting the same estimate of the role ocean expansion played on sea level rise increases confidence in the data and the climate models.

“The models allow us to attribute changes we observe in the paleoclimate record to the physical mechanisms that caused those changes,” Otto-Bliesner said. “This helps tremendously in being able to distinguish mere correlations from cause-and-effect relationships.”

The authors cautioned that past evidence is not a prediction of the future, mostly because global temperatures during the Last Interglacial were driven by changes in Earth’s orbit around the sun. However, current global warming is driven by increasing greenhouse gas concentrations.

The seasonal differences between the northern and the southern hemispheres were more pronounced during the Last Interglacial than they will be in the future.

“We expect something quite different for the future because we’re not changing things seasonally, we’re warming the globe in all seasons,” McKay said.

“The question is, when we think about warming on a global scale and contemplate letting the climate system change to a new warmer state, what would we expect for the ice sheets and sea levels based on the paleoclimate record? The Last Interglacial is the most recent time when sea levels were much higher and it’s a time for which we have lots of data,” McKay added.

“The message is that the last time glaciers and ice sheets melted, sea levels rose by more than eight meters. Much of the world’s population lives relatively close to sea level. This is going to have huge impacts, especially on poor countries,” he added.

“If you live a meter above sea level, it’s irrelevant what causes the rise. Whether sea levels are rising for natural reasons or for anthropogenic reasons, you’re still going to be under water sooner or later.”

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