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.