Science Current Events | Science News | Brightsurf.com
 

Rising oceans -- too late to turn the tide?

July 18, 2011
Melting ice sheets contributed much more to rising sea levels than thermal expansion of warming ocean waters during the Last Interglacial Period, a UA-led team of researchers has found

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 the 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."

###

Reference:

McKay, N., J. T. Overpeck, and B. Otto-Bliesner (2011). The role of ocean thermal expansion in Last Interglacial sea level rise. Geophys. Res. Lett., doi:10.1029/2011GL048280, in press. A version of the accepted paper is available online at the Geophysical Research Letters site: http://www.agu.org/journals/gl/papersinpress.shtml

University of Arizona


Related Sea Level Current Events and Sea Level News Articles


Inland ice in Antarctica melting fast
Many glaciers on the Southern Antarctic Peninsula (SAP) -- a region previously thought to be stable compared to other glacier masses in Antarctica -- became destabilized in 2009, and they have been melting at accelerating rates ever since, researchers say.

Earthquakes reveal deep secrets beneath East Asia
A new work based on 3-D supercomputer simulations of earthquake data has found hidden rock structures deep under East Asia. Researchers from China, Canada, and the U.S. worked together to publish their results in March 2015 in the American Geophysical Union Journal of Geophysical Research, Solid Earth.

New study shows Antarctic ice shelf is thinning from above and below
A decade-long scientific debate about what's causing the thinning of one of Antarctica's largest ice shelves is settled this week (Wednesday 13 May) with the publication of an international study in the journal The Cryosphere.

New national database of coastal flooding launched
Scientists have compiled a new database of coastal flooding in the UK over the last 100 years, which they hope will provide crucial information to help prevent future flooding events.

Focus on the regional impact of climate change
The recently published Second Assessment of Climate Change for the Baltic Sea Basin makes an important contribution to understanding variations in the climate. The report also captures the most important changes to the regional climate in the Kattegat and Baltic Sea areas, home to 90 million people.

The origins and future of Lake Eyre and the Murray-Darling Basin
Geoscientists have, for the first time, discovered the origins of Australia's two largest basins: Lake Eyre and the Murray-Darling Basin. The research also implies that in 30 million years' time both basins will cease to exist.

Dissecting the ocean's unseen waves to learn where the heat, energy and nutrients go
Beyond the pounding surf loved by novelists and beachgoers alike, the ocean contains rolling internal waves beneath the surface that displace massive amounts of water and push heat and vital nutrients up from the deep ocean.

Slowdown after Ice Age sounds a warning for Great Barrier Reef's future
Environmental factors similar to those affecting the present day Great Barrier Reef have been linked to a major slowdown in its growth eight thousand years ago, research led by the University of Sydney, Australia shows.

Gravity data show that Antarctic ice sheet is melting increasingly faster
During the past decade, Antarctica's massive ice sheet lost twice the amount of ice in its western portion compared with what it accumulated in the east, according to Princeton University researchers who came to one overall conclusion -- the southern continent's ice cap is melting ever faster.

Engineering a better future for the Mississippi Delta
River deltas, low-lying landforms that host critical and diverse ecosystems as well as high concentrations of human population, face an uncertain future. Even as some deltas experience decreased sediment supply from damming, others will see increased sediment discharge from land-use changes.
More Sea Level Current Events and Sea Level News Articles

Sea Level

Sea Level
by Sea Level (Author)


Track: 1. Rain In Spain 6:47 2. Shake A Leg 3:53 3. Tidal Wave 5:40 4. Country Fool 3:40 5. Nothing Matters But The Fever 7:20 6. Grand Larceny 5:23 7. Scarborough Fair 5:31 8. Just A Good Feeling 3:01

Handbook of Sea-Level Research (Wiley Works)

Handbook of Sea-Level Research (Wiley Works)
by Professor Ian Shennan (Editor), Antony J. Long (Editor), Benjamin P. Horton (Editor)


Measuring sea-level change – be that rise or fall – is one of the most pressing scientific goals of our time and requires robust scientific approaches and techniques.  This Handbook aims to provide a practical guide to readers interested in this challenge, from the initial design of research approaches through to the practical issues of data collection and interpretation from a diverse range of coastal environments.  Building on thirty years of international research, the Handbook comprises 38 chapters that are authored by leading experts from around the world.  The Handbook will be an important resource to scientists interested and involved in understanding sea-level changes across a broad range of disciplines, policy makers wanting to appreciate our current state of knowledge of...

Sea Level: Adventures of a Saltwater Angler

Sea Level: Adventures of a Saltwater Angler
by Departure Publishing LLC


From Montauk to the Yucatan and beyond, Jeffrey Cardenas, acclaimed author of Marquesa, takes us on a far-flung journey of fly-fishing discovery.

There are tactical passages in this book gleaned from Jeffrey’s many years of guiding in the Florida Keys, but he mainly serves as a passionate and acute narrator, angler, and observer.

He writes about the first 30 seconds of a tarpon hookup, well-endowed redfish in Cajun country, and pelagic marauders capable of burning a half-mile of backing off a fly reel. Along the way he details the intricate relationship between angler, guide, and fish–and he introduces us to a disparate cast of watermen: fly fishing legends, starving Cuban netters, a tuna captain named “Creature”, and a few longtime fishing buddies who molded...

National Geographic Readers: Sea Turtles

National Geographic Readers: Sea Turtles
by Laura Marsh (Author)


Who could resist celebrating sea turtles? They may seem like lazy ocean reptiles drifting with the oceans’ currents, but they are actually long-distance swimmers that spend their entire lives searching for food and a mate. What’s more, they come with their own built-in GPS, returning to the exact beach where they were born to lay their own eggs. Kids will learn all about these tranquil and mysterious animals through brilliant photography and illustrations, plus the trusted and distinctive content you love from NG Kids!

National Geographic Readers: Weird Sea Creatures

National Geographic Readers: Weird Sea Creatures
by Laura Marsh (Author)


Did you know that the deep-sea anglerfish has a glowing fishing rod attached to its body, or that the barreleye fish has a see-through head? See these wacky creatures and more in this brilliantly illustrated book that explores the strangest creatures under the sea. This level two reader uses easy-to-grasp language that will keep children intrigued and learning on every page.

This high-interest, educationally vetted series of beginning readers features the magnificent images of National Geographic, accompanied by texts written by experienced, skilled children's book authors. The inside back cover of the paperback edition is an interactive feature based upon the book. Level 1 books reinforce the content of the book with a kinesthetic learning activity. In Level 2 books readers...

High Tide On Main Street: Rising Sea Level and the Coming Coastal Crisis

High Tide On Main Street: Rising Sea Level and the Coming Coastal Crisis
by John Englander (Author)


NEW 2nd Edition (10-16-13) of best selling book that described a superstorm hitting Atlantic City and New York City -- exactly one week before Sandy. Just one of dozens of scenarios in this amazing book. Find out the other forecasts. Rave reviews from experts and Amazon readers. Fully updated and revised. New Introduction by Governor Christine Todd Whitman. For 6,000 years sea level has changed little. Now it it has started rising again, moving the shoreline too. In clear, easy-to-understand language, this book explains: * The science behind sea level rise, plus the myths and partial truths used to confuse the issue. * The surprising forces that will cause sea level to rise for 1,000 years, as well as the possibility of catastrophic rise this century. * Why the devastating economic...

Sea-Level Science: Understanding Tides, Surges, Tsunamis and Mean Sea-Level Changes

Sea-Level Science: Understanding Tides, Surges, Tsunamis and Mean Sea-Level Changes
by Dr David Pugh (Author), Dr Philip Woodworth (Author)


Understanding sea-level processes, such as ocean tides, storm surges, tsunamis, El Niño and rises caused by climate change, is key to planning effective coastal defence. Building on David Pugh's classic book Tides, Surges and Mean Sea-Level, this substantially expanded, full-colour book now incorporates major recent technological advances in the areas of satellite altimetry and other geodetic techniques (particularly GPS), tsunami science, measurement of mean sea level and analyses of extreme sea levels. The authors discuss how each surveying and measuring technique complements others in providing an understanding of present-day sea-level change and more reliable forecasts of future changes. Giving the how and the why of sea-level change on timescales from hours to centuries, this...

DK Readers: Disasters at Sea (Level 3: Reading Alone)

DK Readers: Disasters at Sea (Level 3: Reading Alone)
by Andrew Donkin (Author)


From fog, ice, and rocks to cannon fire and torpedo attacks--read the story of five doomed sea voyages and the fate of those who took part in them. The 48-page Level 3 books, designed for children who can read on their own, contain more complex sentence structure and more detail. Young readers will devour these kid-friendly titles, which cover high-interest topics such as sharks, and the Bermuda Triangle, as well as classics like Aladdin. Information boxes highlight historical references, trivia, pronunciation, and other facts about words and names mentioned. Averaging 2,400 to 2,800 words, these books offer a 50/50 picture-to-text ratio. The Dorling Kindersley Readers combine an enticing visual layout with high-interest, easy-to-read stories to captivate and delight young bookworms who...

Last Psalm at Sea Level

Last Psalm at Sea Level
by Meg Day (Author)


Poetry. LGBT Studies. "Lovely does not suffice, nor does lyric. Eloquence is only a grasping in the space of ineffable air. There are few words or phrases that do justice to the soul singing its own revelations. That place is where LAST PSALM AT SEA LEVEL lives, where it is as solid as gold burning itself into light."—Afaa Michael Weaver

The Sedimentary Record of Sea-Level Change

The Sedimentary Record of Sea-Level Change
by Angela L. Coe (Author), Dan W. J. Bosence (Author), Kevin D. Church (Author), Stephen S. Flint (Author), John A. Howell (Author), R. Chris L. Wilson (Author)


This illustrated textbook describes how past changes in sea-level can be detected through an analysis of the sedimentary record, and how sequence stratigraphy techniques can provide explanations of how the sedimentary system evolves through geological time. Designed for use in undergraduate and graduate courses, it includes detailed case studies, set-aside focus boxes, and bulleted Questions and Answers interspersed throughout. The book is also supported by a website hosting sample pages.

© 2015 BrightSurf.com