ANTÁRTICA: NASA: La Antártida gana más hielo del que pierde. NASA Study: Mass Gains of Antarctic Ice Sheet Greater than Losses

NASA Study: Mass Gains of Antarctic Ice Sheet Greater than Losses

A new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers.

The research challenges the conclusions of other studies, including the Intergovernmental Panel on Climate Change’s (IPCC) 2013 report, which says that Antarctica is overall losing land ice.

According to the new analysis of satellite data, the Antarctic ice sheet showed a net gain of 112 billion tons of ice a year from 1992 to 2001. That net gain slowed   to 82 billion tons of ice per year between 2003 and 2008.

“We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica,” said Jay Zwally, a glaciologist with NASA Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study, which was published on Oct. 30 in the Journal of Glaciology. “Our main disagreement is for East Antarctica and the interior of West Antarctica – there, we see an ice gain that exceeds the losses in the other areas.”  Zwally added that his team “measured small height changes over large areas, as well as the large changes observed over smaller areas.”

Scientists calculate how much the ice sheet is growing or shrinking from the changes in surface height that are measured by the satellite altimeters. In locations where the amount of new snowfall accumulating on an ice sheet is not equal to the ice flow downward and outward to the ocean, the surface height changes and the ice-sheet mass grows or shrinks.

But it might only take a few decades for Antarctica’s growth to reverse, according to Zwally. “If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they’ve been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years -- I don’t think there will be enough snowfall increase to offset these losses.”

The study analyzed changes in the surface height of the Antarctic ice sheet measured by radar altimeters on two European Space Agency European Remote Sensing (ERS) satellites, spanning from 1992 to 2001, and by the laser altimeter on NASA’s Ice, Cloud, and land Elevation Satellite (ICESat) from 2003 to 2008.

Zwally said that while other scientists have assumed that the gains in elevation seen in East Antarctica are due to recent increases in snow accumulation, his team used meteorological data beginning in 1979 to show that the snowfall in East Antarctica actually decreased by 11 billion tons per year during both the ERS and ICESat periods. They also used information on snow accumulation for tens of thousands of years, derived by other scientists from ice cores, to conclude that East Antarctica has been thickening for a very long time. 

“At the end of the last Ice Age, the air became warmer and carried more moisture across the continent, doubling the amount of snow dropped on the ice sheet,” Zwally said.

The extra snowfall that began 10,000 years ago has been slowly accumulating on the ice sheet and compacting into solid ice over millennia, thickening the ice in East Antarctica and the interior of West Antarctica by an average of 0.7 inches (1.7 centimeters) per year. This small thickening, sustained over thousands of years and spread over the vast expanse of these sectors of Antarctica, corresponds to a very large gain of ice – enough to outweigh the losses from fast-flowing glaciers in other parts of the continent and reduce global sea level rise.  

Zwally’s team calculated that the mass gain from the thickening of East Antarctica remained steady from 1992 to 2008 at 200 billion tons per year, while the ice losses from the coastal regions of West Antarctica and the Antarctic Peninsula increased by 65 billion tons per year.

“The good news is that Antarctica is not currently contributing to sea level rise, but is taking 0.23 millimeters per year away,” Zwally said. “But this is also bad news. If the 0.27 millimeters per year of sea level rise attributed to Antarctica in the IPCC report is not really coming from Antarctica, there must be some other contribution to sea level rise that is not accounted for.”

“The new study highlights the difficulties of measuring the small changes in ice height happening in East Antarctica,” said Ben Smith, a glaciologist with the University of Washington in Seattle who was not involved in Zwally’s study.

"Doing altimetry accurately for very large areas is extraordinarily difficult, and there are measurements of snow accumulation that need to be done independently to understand what’s happening in these places,” Smith said. 

To help accurately measure changes in Antarctica, NASA is developing the successor to the ICESat mission, ICESat-2, which is scheduled to launch in 2018. “ICESat-2 will measure changes in the ice sheet within the thickness of a No. 2 pencil,” said Tom Neumann, a glaciologist at Goddard and deputy project scientist for ICESat-2. “It will contribute to solving the problem of Antarctica’s mass balance by providing a long-term record of elevation changes.”

Map showing the rates of mass changes from ICESat 2003-2008 over Antarctica. Sums are for all of Antarctica: East Antarctica (EA, 2-17); interior West Antarctica (WA2, 1, 18, 19, and 23); coastal West Antarctica (WA1, 20-21); and the Antarctic Peninsula (24-27). A gigaton (Gt) corresponds to a billion metric tons, or 1.1 billion U.S. tons.

Credits: Jay Zwally/Journal of Glaciology

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María José Viñas

NASA Earth Science News Team

NASA: La Antártida gana más hielo del que pierde

Foto de la Península Antártica una de las zonas que está perdiendo hielo desde hace décadas

Fuente: NASA

Es verdad que el descongelamiento de los polos se ha acelerado. Sin embargo, un estudio realizado por la NASA sostiene que estas pérdidas se compensan con un incremento glaciar en otras zonas del continente.

Una investigación pone en duda las conclusiones de diversos estudios que dicen que a grandes rasgos la Antártida está perdiendo territorio glacial, como, por ejemplo, el informe del Grupo Intergubernamental de Expertos sobre el Cambio Climático (IPCC) presentado en el 2013.

“Estamos de acuerdo con otros estudios que demuestran una aceleración en el deshielo de la Península Antártica y los glaciares de la región de Pine Island y Thwaites en la zona oeste de la Antártida.” afirmó Jay Zally, glaciólogo del NASA Goddard Space Flight Center en Greenbelt, Maryland y principal autor de la investigación. “Nuestro mayor desacuerdo es sobre el este de la Antártida y el interior de la parte oeste – ahí vemos un incremento de hielo superior a las pérdidas detectadas en las otras zonas.”

De acuerdo a la investigación, estas ganancias provienen de una acumulación de nieve que empezó 10,000 años atrás. “Durante la última Era del Hielo, el aire se calentó y aumentó la humedad en ciertas zonas del continente haciendo que los niveles de nieve que caían se duplicaran.” Con el tiempo esta nieve extra se ha ido convirtiendo en hielo sólido, haciendo que ciertas zonas de la Antártica crezcan 1.7 centímetros por año. Este paulatino engrosamiento del hielo ha hecho posible que se equilibren las pérdidas en otras zonas y que los niveles de agua del océano se reduzcan.

Sin embargo, Zally advierte que si la tasa de deshielo sigue incrementando a la velocidad a la que lo está haciendo, dentro de 20 o 30 años las pérdidas de hielo alcanzarán el volumen de la acumulación generada en la zona este de la Antártida y entonces el continente comenzará a perder su tamaño. “No creo que entonces la caída de nieve alcance los niveles suficientes para contrarrestar el deshielo.”

La aceleración del deshielo

Según la data recolectada por los satélites de la NASA, entre 1992 y 2001 el inlandsis antártico (cubierta de hielo que cubre el 98 % del polo sur) ganaba 112 mil millones de toneladas netas de hielo al año. En el periodo 2003-2008 la tasa neta anual disminuyó considerablemente a 82 mil millones de toneladas de hielo.

La masa del engrosamiento de Antártida del Este ha sido calculada en una tasa estable de 200 mil millones de toneladas al año en el periodo 1992-2008. Mientras que las pérdidas en las zonas costeras de Antártica del Oeste y la Península Antártica han incrementado a 65 mil millones de toneladas por año.

El problema con el nivel del mar

La investigación revela que en lugar de contribuir con el incremento del nivel de agua del océano, la Antártida está reduciéndolo 0.23 milímetros por año. Sin embargo, estas noticias no son del todo buenas. El nivel del mar sigue incrementando 0.27 milímetros por año… la pregunta es: si no proviene del deshielo de la Antártida, ¿qué está haciendo que los niveles de agua marina incrementen? 

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