Fastest Sea-Level Rise in Two Millennia Linked to Increasing Global Temperatures

Rate is greater now than at any time during past 2,100 years

The rate of sea level rise along the U.S. Atlantic coast is greater now than at any time in the past 2,000 years--and has shown a consistent link between changes in global mean surface temperature and sea level. The findings are published this week in the journal Proceedings of the National Academy of Sciences (PNAS).

The research, funded by the National Science Foundation (NSF), was conducted by Andrew Kemp, Yale University; Benjamin Horton, University of Pennsylvania; Jeffrey Donnelly, Woods Hole Oceanographic Institution; Michael Mann, Pennsylvania State University; Martin Vermeer, Aalto University School of Engineering, Finland; and Stefan Rahmstorf, Potsdam Institute for Climate Impact Research, Germany.

"Having a detailed picture of rates of sea level change over the past two millennia provides an important context for understanding current and potential future changes," says Paul Cutler, program director in NSF's Division of Earth Sciences.

"It's especially valuable for anticipating the evolution of coastal systems," he says, "in which more than half the world's population now lives."

Adds Kemp, "Scenarios of future rise are dependent on understanding the response of sea level to climate changes. Accurate estimates of past sea-level variability provide a context for such projections."

Kemp and colleagues developed the first continuous sea-level reconstruction for the past 2,000 years, and compared variations in global temperature to changes in sea level over that time period.

The team found that sea level was relatively stable from 200 BC to 1,000 AD. Then in the 11th century, sea level rose by about half a millimeter each year for 400 years, linked with a warm climate period known as the Medieval Climate Anomaly.

Then there was a second period of stable sea level during a cooler period called the Little Ice Age. It persisted until the late 19th century. Since the late 19th century, sea level has risen by more than 2 millimeters per year on average, the steepest rate for more than 2,100 years.

"Sea-level rise is a potentially disastrous outcome of climate change," says Horton, "as rising temperatures melt land-based ice, and warm ocean waters."

To reconstruct sea level, the scientists used microfossils called foraminifera preserved in sediment cores extracted from coastal salt marshes in North Carolina. The age of the cores was estimated using radiocarbon dating and other techniques.

To test the validity of their approach, the team compared its reconstructions with tide-gauge measurements from North Carolina for the past 80 years, and global tide-gauge records for the past 300 years.

A second reconstruction from Massachusetts confirmed their findings.

The records were corrected for contributions to sea-level rise made by vertical land movements.

The reconstructed changes in sea level over the past millennium are consistent with past global temperatures, the researchers say, and can be determined using a model relating the rate of sea level rise to global temperature.

"Data from the past helped calibrate our model, and will improve sea level rise projections under scenarios of future temperature increases," says Rahmstorf.

Support for the research also was provided by the National Oceanic and Atmospheric Administration, United States Geological Survey, the Academy of Finland, the European Science Foundation through European Cooperation in Science and Technology and the University of Pennsylvania.

New Map Reveals Giant Fjords Beneath East Antarctic Ice Sheet

 

ScienceDaily (June 1, 2011) — Scientists from the U.S., U.K. and Australia have used ice-penetrating radar to create the first high- resolution topographic map of one of the last uncharted regions of Earth, the Aurora Subglacial Basin, an immense ice-buried lowland in East Antarctica larger than Texas.

The map reveals some of the largest fjords or ice cut channels on Earth, providing important insights into the history of ice in Antarctica. The data will also help computer modelers improve their simulations of the past and future Antarctic ice sheet and its potential impact on global sea level.

"We knew almost nothing about what was going on, or could go on, under this part of the ice sheet and now we've opened it up and made it real," said Duncan Young, research scientist at The University of Texas at Austin's Institute for Geophysics and lead author on the study, which appears in the journal Nature.

"We chose to focus on the Aurora Subglacial Basin because it may represent the weak underbelly of the East Antarctic Ice Sheet, the largest remaining body of ice and potential source of sea-level rise on Earth," said Donald Blankenship, principal investigator for the ICECAP project, a multinational collaboration using airborne geophysical instruments to study the ice sheet.

Because the basin lies kilometers below sea level, seawater could penetrate beneath the ice, causing portions of the ice sheet to collapse and float off to sea. Indeed, this work shows that the ice sheet has been significantly smaller in the past.

Previous work based on ocean sediments and computer models indicates the East Antarctic Ice Sheet grew and shrank widely and frequently, from about 34 to 14 million years ago, causing sea level to fluctuate by 200 feet . Since then, it has been comparatively stable, causing sea-level fluctuations of less that 50 feet. The new map reveals vast channels cut through mountain ranges by ancient glaciers that mark the edge of the ice sheet at different times in the past, sometimes hundreds of kilometers from its current edge.

"We're seeing what the ice sheet looked like at a time when Earth was much warmer than today," said Young. "Back then it was very dynamic, with significant surface melting. Recently, the ice sheet has been better behaved."

However, recent lowering of major glaciers near the edge detected by satellites has raised concerns about this sector of Antarctica.

Young said past configurations of the ice sheet give a sense of how it might look in the future, although he doesn't foresee it shrinking as dramatically in the next 100 years. Still, even a small change in this massive ice sheet could have a significant effect on sea level. Scientists at The University of Texas at Austin's Institute for Computational Engineering and Sciences, and at Australia's Antarctic Climate and Ecosystems CRC are developing models that will use the new map to forecast how the ice sheet will evolve in the future and how it might affect sea level.

This research is part of ICECAP (Investigating the Cryospheric Evolution of the Central Antarctic Plate), a joint project of The University of Texas at Austin's Jackson School of Geosciences, the University of Edinburgh and the Australian Antarctic Division. For three field seasons, the team flew an upgraded World War II-era DC-3 aircraft with a suite of geophysical instruments to study the ice and underlying rock in East Antarctica.

Funding for this research is provided by the National Science Foundation (U.S.), the National Aeronautics and Space Administration (U.S.), the Natural Environment Research Council (U.K.), the Australian Antarctic Division, the G. Unger Vetlesen Foundation (U.S.), the Antarctic Climate and Ecosystems CRC (Aus.), and the University of Texas at Austin's Jackson School of Geosciences (U.S.).

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Journal Reference:

1. Duncan A. Young, Andrew P. Wright, Jason L. Roberts, Roland C. Warner, Neal W. Young, Jamin S. Greenbaum, Dustin M. Schroeder, John W. Holt, David E. Sugden, Donald D. Blankenship, Tas D. van Ommen, Martin J. Siegert. A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes. Nature, 2011; 474 (7349): 72 DOI: 10.1038/nature10114

Farm Runoff in Mississippi River Floodwater Fuels Dead Zone in Gulf

By: Jenny Marder

A dead zone -- already the size of the state of New Jersey -- is growing in the Gulf of Mexico, fueled by nutrient runoff from the swollen Mississippi River.

This year, with floodwaters from the Birds Point levee breach and the Morganza and Bonnet Carret spillways spreading over farmland and other residential areas, the river is collecting tremendous amounts of fertilizer and pesticides. This is contributing to what scientists say may become the largest dead zone ever, and posing a serious threat to already taxed marine life.

During the rainy season, fertilizer, animal waste, sewage and car exhaust wash into the Mississippi and the Atchafalaya rivers, flow south and empty into the mouth of the Gulf.

Nitrogen and phosphorous from farm runoff and animal waste are especially toxic to ocean life. They act as natural fertilizers, feeding harmful algae and causing it to bloom wildly. As bacteria consume these blooms, they suck oxygen from the water, depleting the ocean's oxygen reserves. Scientists call this oxygen depletion hypoxia.

"We're expecting probably the largest-ever amount of hypoxia," said Nancy Rabalais, a marine scientist and executive director of the Louisiana Universities Marine Consortium. "That's the the prediction based on the amount of nitrogen coming down the river."

A surge of fresh water creates a layering effect in the seawater, which compounds the problem. The freshwater sits above the heavier saltwater, acting as a cap that prevents oxygen from reaching the deeper water levels.

"The bottom layer of the ocean gets so low in oxygen that sea life has to swim away and vacate the area, and if they can't get away, they suffocate," said Matt Rota, science and water policy director for the Gulf Restoration Network.

Flooding could cause further injury to fisheries in the northern Gulf of Mexico, already reeling from last year's oil spill, Rabalais said. Dead zones alter the habitat for crab, shrimp, fish and lobster, often forcing them to shallow areas. This includes catchable seafood, like shrimp and snapper, which are vital to the area's fisheries. "A lot of the Louisiana shrimp fisheries use smaller vessels," Rabalais said. "With the price of fuel and the distance they have to go, they might opt not to go offshore."

Possibly the largest source of nutrients comes from farms in Illinois, Iowa, Ohio and southwest Minnesota, where drainage tiles -- plastic pipes that crisscross underground - - drain the once-wet soil, making it arable, and dry enough for corn and soybean crops. But these pipes also flush nitrogen fertilizer into tributaries, which lead to rivers and eventually the Gulf.

In fact, research shows that the most heavily tile-drained areas of North America also contribute the largest source of nitrates to the Gulf of Mexico, which add to the dead zone, according to Mark David, a professor of biogeochemistry from the University of Illinois.

David is researching options for reducing nitrate levels. They include valves and beds of woodchips inside the tiles, as well as restoring wetlands, which filter pollution naturally.

It's not the farmers' fault, David said, but there's little incentive for farmers to reduce their nitrate output. 

"There's a fundamental problem in the whole system if we really want to reduce nitrate and phosphorous loss from the system. Everything's been voluntary up to this point, and that hasn't gotten us anywhere."

Competition for krill links a rebounding ecosystem to penguin declines

By  Emmett Duffy 

 

At the far bottom of the earth, at the bitter end of the Pacific Ocean, lies the Ross Sea, home to a large proportion of the world’s penguins. Although it’s often considered the last intact marine ecosystem on earth, it appears there is no escape here, nor anywhere else, from the invisible miasma of CO2 produced by modern society. But, as a new study in PNAS shows, the impacts of changing climate are not simple — they interact through a complex network of food-web interactions with legacies of fishing and whaling, ultimately rippling out to the region’s penguins. And a key link — the one ring to rule them all — is krill.

The recent story of two penguin species in the region has posed a puzzle: Adelies hang out on the pack ice in winter, whereas chinstraps forage in the open water, meaning that they should show opposite responses to the declining ice cover caused by climate warming.

 

And in the late 70s and early 80s they did as expected: Adelies declined with melting ice whereas chinstraps prospered in the opening water. But since then both species have declined steadily. What’s up?

The paradoxical history of penguins over the last century appear to result from a complex interplay between the twin horsemen of climate change and human harvesting — in this case fishing and whaling (see the figure).  It’s long been suspected that the relentless human pressure on every other vertebrate in the southern ocean proved a boon for penguins as competition for krill was reduced. First there was the hunting of the Antarctic fur seal in the 19th century, then the decimation of whales during the wild-west days of the early 20th century, and finally the fishery for icefishes over recent decades. Indeed, penguin numbers climbed during much of the 20th century.

But as conservation measures have kicked in, the whales and seals have  begun to rebound and the region’s fisheries have come under more conservative management. On top of this a trawl fishery for krill was established, all of which leads to more mouths going after the central resource of the Southern Ocean — krill. And the penguins find themselves caught between the pincers of declining sea-ice habitat and declining food.

And there is another issue. As the New York Times summarizes:

“The Ross Sea is projected to be the last place on Earth where sea ice will endure. But as the annual winter sea ice boundary retreats farther south, pack ice penguins may ultimately find themselves trapped behind a curtain of polar night for which they have no hardwired strategy.

Indeed, Dr. Ainley speculates, Adélie penguins face possible extinction not merely by a loss of habitat — but by an unshakable fear of darkness.”

Original source (open access): Wayne Z. Trivelpiecea, Jefferson T. Hinkea, Aileen K. Millera, Christian S. Reissa, Susan G. Trivelpiecea, and George M. Watters. 2011. Variability in krill biomass links harvesting and climate warming to penguin population changes in Antarctica. PNAS 108(18):7625-7628.

West Antarctic Warming Triggered by Warmer Sea Surface in Tropical Pacific

ScienceDaily (Apr. 10, 2011) — The Antarctic Peninsula has warmed rapidly for the last half-century or more, and recent studies have shown that an adjacent area, continental West Antarctica, has steadily warmed for at least 30 years, but scientists haven't been sure why.

New University of Washington research shows that rising sea surface temperatures in the area of the Pacific Ocean along the equator and near the International Date Line drive atmospheric circulation that has caused some of the largest shifts in Antarctic climate in recent decades.

The warmer water generates rising air that creates a large wave structure in the atmosphere called a Rossby wave train, which brings warmer temperatures to West Antarctica during winter and spring.

Antarctica is somewhat isolated by the vast Southern Ocean, but the new results "show that it is still affected by climate changes elsewhere on the planet," said Eric Steig, a UW professor of Earth and space sciences and director of the UW Quaternary Research Center.

Steig is the corresponding author of a paper documenting the findings that is being published April 10 in the journal Nature Geoscience. The lead author is Qinghua Ding, a postdoctoral researcher in the UW Quaternary Research Center. Co-authors are David Battisti, a UW atmospheric sciences professor, and Marcel Küttel, a former UW postdoctoral researcher now working in Switzerland.

The scientists used surface and satellite temperature observations to show a strong statistical connection between warmer temperatures in Antarctica, largely brought by westerly winds associated with high pressure over the Amundsen Sea adjacent to West Antarctica, and sea surface temperatures in the central tropical Pacific Ocean.

They found a strong relationship between central Pacific sea-surface readings and Antarctic temperatures during winter months, June through August. Though not as pronounced, the effect also appeared in the spring months of September through November.

The observed circulation changes are in the form of a series of high- and low-pressure cells that follow an arcing path from the tropical Pacific to West Antarctica. That is characteristic of a textbook Rossby wave train pattern, Ding said, and the same pattern is consistently produced in climate models, at least during winter.

Using observed changes in tropical sea surface temperatures, the researchers found they could account for half to all of the observed winter temperature changes in West Antarctica, depending on which observations are used for comparison.

"This is distinct from El Niño," Steig said. That climate phenomenon, which affects weather patterns worldwide, primarily influences sea-surface temperatures farther east in the Pacific, nearer to South America. It can be, but isn't always, associated with strong warming in the central Pacific.

Steig noted that the influence of Rossby waves on West Antarctic climate is not a new idea, but this is the first time such waves have been shown to be associated with long-term changes in Antarctic temperature.

The findings also could have implications for understanding the causes behind the thinning of the West Antarctic Ice Sheet, which contains about 10 percent of all the ice in Antarctica.

Steig noted that the westerly winds created by the high pressure over the Amundsen Sea pushes cold water away from the edge of the ice sheet and out into the open ocean. It is then replaced by warmer water from deeper in the ocean, which is melting the seaward edge of the ice sheet from below.

The work was funded by the National Science Foundation.

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Journal Reference:

1. Qinghua Ding, Eric J. Steig, David S. Battisti, Marcel Küttel. Winter warming in West Antarctica caused by central tropical Pacific warming. Nature Geoscience, 2011; DOI: 10.1038/ngeo1129

Climate Change Poses Major Risks for Unprepared Cities

 

Fast-growing urban areas most likely to feel the heat

People in urban areas like Mexico City are especially at risk from the effects of climate change.

April 7, 2011

Cities worldwide are failing to take necessary steps to protect residents from the likely impacts of climate change, even though billions of urban dwellers are vulnerable to heat waves, sea level rise and other changes associated with warming temperatures.

A new examination of urban policies by Patricia Romero Lankao at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., in conjunction with an international research project on cities and climate change, warns that many of the world's fast-growing urban areas, especially in developing countries, will likely suffer disproportionately from the impacts of changing climate.

Her work also concludes that most cities are failing to reduce emissions of carbon dioxide and other greenhouse gases that affect the atmosphere. "Climate change is a deeply local issue and poses profound threats to the growing cities of the world," says Romero Lankao. "But too few cities are developing effective strategies to safeguard their residents."

Romero Lankao's studies appear this month in a special issue of Current Opinion in Environmental Sustainability and in a synthesis article in an upcoming issue of European Planning Studies. The research was conducted in association with the United Nations Human Settlements Programme (UN-HABITAT) and funded by the National Science Foundation (NSF), NCAR's sponsor.

"Cities are major sources of greenhouse gases, yet at the same time urban populations are likely to be among those most severely affected by future climate change," says Sarah Ruth, program director in NSF's Division of Atmospheric and Geospace Sciences, which funds NCAR.

"The findings highlight ways in which city-dwellers are particularly vulnerable, and suggest policy interventions that could offer immediate and longer-term benefits."

Romero Lankao, a sociologist specializing in climate change and urban development, surveyed policies in cities worldwide while drawing on a number of recent studies of climate change and cities.

She concluded that cities are falling short in two areas: preparing for the likely impacts of climate change and cutting their own greenhouse gas emissions by reducing fossil fuel use.

With more than half the world's population living in cities, scientists are increasingly focusing on the potential impacts of climate change on these areas.

The locations and dense construction patterns of cities often place their populations at greater risk for natural disasters, including those expected to worsen with climate change.

Potential threats associated with climate include storm surges that can inundate coastal areas and prolonged hot weather that can heat heavily paved cities more than surrounding areas.

The impacts of such natural events can be magnified in an urban environment. For example, a prolonged heat wave can exacerbate existing levels of air pollution, causing widespread health problems.

Poorer neighborhoods that may lack basic facilities such as reliable sanitation, drinking water or a dependable network of roads, are especially vulnerable to natural disasters.

Moreover, populations are increasing most quickly in small- and medium-sized urban areas, which often lack the services and infrastructure to manage the rapid influx, according to Romero Lankao.

The number of urban residents worldwide has quadrupled since 1950, and cities are continuing to grow rapidly, especially in developing nations.

Romero Lankao cites projections that, by 2020, there will be more than 500 urban areas with 1 million or more residents. Many residents in poorer countries live in substandard housing without access to reliable drinking water, roads and basic services. Neighborhoods sometimes spring up on steep hillsides or floodplains, leaving them vulnerable to storms.

But even on the heels of deadly catastrophes that scientists say will become more common with climate change, such as flash floods in Rio de Janeiro or heat waves in Europe, leaders are often failing to reinforce their defenses against natural disasters.

Romero Lankao cites three reasons for the failure to prepare: fast-growing cities are overwhelmed with other needs, city leaders are often under pressure to downplay the need for health and safety standards in order to foster economic growth and climate projections are rarely fine-scale enough to predict impacts on individual cities.

"Local authorities tend to move towards rhetoric rather than meaningful responses," Romero Lankao writes. "What is at stake, of course, is the very existence of many human institutions, and the safety and well-being of masses of humans."

Cities are also failing in many cases to curb their own emissions of greenhouse gases, the study finds. Instead of imposing construction standards that could reduce heating and air conditioning needs or guiding development to emphasize mass transit and reduce automobile use, many local governments are taking a hands-off approach.

"Cities can have an enormous influence on emissions by focusing on mass transit systems and energy efficient structures," Romero Lankao says. "But local leaders face pressures to build more roads and relax regulations that could reduce energy use."

The study also cites efforts in some cities to reduce emissions as part of a larger strategy to ease traffic and other problems.

For example, central London's Congestion Charging Zone is intended to encourage more use of mass transit. And several Latin American cities, such as Curitiba, Brazil, and Bogota, Colombia, are integrating new development with mass transit systems.

As cities attempt to meet the needs of their low-income residents, some strategies-including moving residents away from risk-prone areas and improving housing and services-may also improve their readiness for a changing climate.

"As hubs of development, cities have shown that they can become sources of innovation," Romero Lankao says.

"The good news is that policymakers can discover ways to improve sanitation, health and safety as they try to reduce emissions and adapt to climate impacts."

Glaciers in Chile 'melt at fastest rate in 350 years'

San Rafael Glacier in Patagonia, one of the 270 glaciers included in this study, has retreated about 8km since the peak of the 'Little Ice Age'.

 

Melting mountain glaciers are making sea levels rise faster now than at any time in the last 350 years, according to new research. Universities at Aberystwyth, Exeter and Stockholm looked at longer timescales than usual for their study.They mapped changes in 270 of the largest glaciers between Chile and Argentina since the "Little Ice Age".

Studies showed glaciers have lost volume on average "10 to 100 times faster" in the last 30 years. The rapid melt rate is linked to their contribution to global sea level. The new research was published in the journal Nature Geoscience on Sunday. Their survey centered on remotely sensed images of outlet glaciers of the south and north Patagonian icefields, but used longer timescales than previous studies.

Satellite image of Upsala Glacier in Patagonia, which has retreated about 13km since 1750.

 

The glaciers straddle the Andes, on the border between Chile and Argentina. The northern icefield extends for nearly 200 km and covers a surface of 4,200 square km, while the southern icefield is more than 350km long, covering 13,000 square km. 

The scientists mapped changes in the position of the glaciers since the "Little Ice Age". This took place around 1870 for the north icefield and around 1650 for the southern icefield, the last time that they were much larger in the recent past.

Lead author, Professor Neil Glasser of Aberystwyth University, said: "Previous estimates of sea-level contribution from mountain glaciers are based on very short timescales. "They cover only the last 30 years or so when satellite images can be used to calculate rates of glacier volume change. "We took a different approach by using a new method that allows us to look at longer timescales.

 

'Above-average'

"We knew that glaciers in South America were much bigger during the Little Ice Age so we mapped the extent of the glaciers at that time and calculated how much ice has been lost by the retreat and thinning of the glaciers." Their calculations showed that in recent years the mountain glaciers have rapidly increased their melt rate and thus their contribution to global sea level.

Dr Stephen Harrison of the University of Exeter, added: "The work is significant because it is the first time anyone has made a direct estimate of the sea-level contribution from glaciers since the peak of the industrial revolution (between 1750-1850). "

He said their results showed that estimates taken a decade ago of rates of glacier contribution to sea-level rise are "well above" the long-term averages, which cover 1650/1750 to 2010 and 1870-2010.