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


NOAA analysis reveals significant land cover changes in US coastal regions
A new NOAA nationwide analysis shows that between 1996 and 2011, 64,975 square miles in coastal regions--an area larger than the state of Wisconsin--experienced changes in land cover, including a decline in wetlands and forest cover with development a major contributing factor.

Megascale icebergs run aground: Finding the deepest iceberg scours to date provides new insights into the Arctic's glacial past
Scientists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), have found between Greenland and Spitsbergen the scours left behind on the sea bed by gigantic icebergs.

Northern Pacific's tropical anoxic zone might shrink from climate change
A commonly held belief that global warming will diminish oxygen concentrations in the ocean looks like it may not be entirely true. According to new research published in Science magazine, just the opposite is likely the case in the northern Pacific Ocean, with its anoxic zone expected to shrink in coming decades because of climate change.

Atlantic warming turbocharges Pacific trade winds
New research has found rapid warming of the Atlantic Ocean, likely caused by global warming, has turbocharged Pacific Equatorial trade winds. Currently the winds are at a level never before seen on observed records, which extend back to the 1860s.

Atlantic origin of recent Pacific trade wind, sea level and temperature trends
An Australian-US team of climate researchers has solved a puzzle that has challenged scientists for over a decade.

Conservation scientists asking wrong questions on climate change impacts on wildlife
Scientists studying the potential effects of climate change on the world's animal and plant species are focusing on the wrong factors, according to a new paper by a research team from the Wildlife Conservation Society, University of Queensland, and other organizations.

NRL Reveals New Meteorological Insight into Mid-Level Clouds
Research meteorologists at the U.S. Naval Research Laboratory (NRL) Marine Meteorology Division (MMD) and Scripps Institution of Oceanography, employing the Navy's Mid-Course Doppler Radar (MCR) at Cape Canaveral, were able to characterize mid-level, mixed-phase altocumulus clouds.

UM-led research team contributes to the management of South Florida coastal environments
A Florida-based marine research team has developed a unique formal process and modeling framework to help manage South Florida's economically important coastal marine environments.

CU, Old Dominion team finds sea level rise in western tropical Pacific anthropogenic
A new study led by Old Dominion University and the University of Colorado Boulder indicates sea levels likely will continue to rise in the tropical Pacific Ocean off the coasts of the Philippines and northeastern Australia as humans continue to alter the climate.

The rate at which groundwater reservoirs are being depleted is increasing
In what parts of the world and to what degree have groundwater reservoirs been depleted over the past 50 years? The Frankfurt hydrologist Prof. Petra Döll has been researching this using the global water model WaterGAP.
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

Last Psalm at Sea Level

Last Psalm at Sea Level
by Meg Day (Author)


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 Attacking Ocean: The Past, Present, and Future of Rising Sea Levels

The Attacking Ocean: The Past, Present, and Future of Rising Sea Levels
by Brian Fagan (Author)


The past fifteen thousand years—the entire span of human civilization—have witnessed dramatic sea level changes, which began with rapid global warming at the end of the Ice Age, when coastlines were more than seven hundred feet below modern levels. Over the next ten millennia, the oceans climbed in fits and starts. These rapid changes had little effect on those humans who experienced them, partly because there were so few people on earth, and also because those people were able to adjust readily to new coastlines.

Global sea levels stabilized about six thousand years ago, except for local adjustments that caused often significant changes to places such as the Nile Delta. The curve of inexorably rising seas flattened out as urban civilizations developed in Egypt, Mesopotamia,...

Scholastic Reader Level 1: The Sea Monster: A Steve and Wessley Reader

Scholastic Reader Level 1: The Sea Monster: A Steve and Wessley Reader
by Jennifer E. Morris (Author)


Steve and Wessley are back in the hilarious follow-up to THE ICE CREAM SHOP!

There is something in the pond. Wessley thinks it's just a stick. But Steve thinks it may be something much scarier....

Readers will love the second outing of hilarious duo Steve and Wessley, two friends who always seem to get into the silliest situations!

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!

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: 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...

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...

DK Readers: Pirates: Raiders of the High Seas (Level 4: Proficient Readers)

DK Readers: Pirates: Raiders of the High Seas (Level 4: Proficient Readers)
by Christopher Maynard (Author), Harriet Griffey (Author), Harriet Griffey (Contributor)


Meet Pirates who got away with murder... and pirates who died in the hangman's noose! These 48-page books about fascinating subjects like pirates, mummies, and volcanoes are for proficient readers who can understand a rich vocabulary and challenging sentence structure. In addition to the stunning photographs, informative sidebars, and glossary, readers will find archival photographs and paintings. Averaging 4,500 to 5,000 words in length, Level 4 books are 40 percent pictures and 40 percent text. The Dorling Kindersley Readers combine an enticing visual layout with high-interest, easy-to-read stories to captivate and delight young bookworms who are just getting started. Written by leading children's authors and compiled in consultation with literacy experts, these engaging books build...

Scholastic Reader Level 1: Seahorses

Scholastic Reader Level 1: Seahorses
by Nicole Corse (Author)


A closer look at an amazing animal!

This reader will provide an introduction to seahorses bringing simple and fun nonfiction information to young readers. Did you know sea horses have to eat all the time to stay alive? In Seahorses, readers will discover where seahorses live, what they eat, what eats them, how they are different from other sea creatures, and how people can help prevent their extinction.


© 2014 BrightSurf.com