Nuevo estudio,
Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure sugiere que los modelos usados actualmente subestiman el derretimiento de las capas de hielo en la Antártida , ya que con ellos no se puede explicar el dramático aumento del nivel del mar registrado en épocas como el
Plioceno ,cuando el nivel del mar era
20 metros mayor que el actual ,ver
aquí y la temperatura era 2-3 C mas con una concentración de 400ppm de Co2..
Los modelos actuales solo simulan
2 a 7 metros de los actuales 20mts de variación que se derivan de los datos paleoclimáticos , en las condiciones de temperatura de esa época, y lo mas importante, aun asumiendo el derretimiento total de
Groenlandia (+7mts) y la plataforma WAIS en la
Antártida (+3mts), esto aportaría unos 10 metros , aun quedando por explicar que fue lo que contribuyo con los restantes 10mts , y entonces es claro, que la respuesta no puede ser otra que una buena parte de plataforma
Antártica EAIS , que la mayoría de los modelos estiman como estable o muy estable , a variaciones de temperatura inferiores a los 4 o 6 grados , no lo lo sería tanto ..
ftp://rock.geosociety.org/pub/reposit/2012/2012112.pdfPara tratar de subsanar esta discrepancia entre modelos , y lo datos plaeoclimáticos , el estudio agrega dos parámetros físicos que han sido estudiados recientemente, y se sabe de sus efectos ,pero no habían sido modelizados antes ,
hydrofracture y ice-cliff failure El resultado fue que se obtuvieron, valores de deshielo y colapso de EAIS y WAIS mucho mas realistas que sin , estos parámetros , y mucho mas consistentes con los datos paleoclimáticos que sugieren un a gran contribución de EAIS y unos +20 de nivel del mar..
Y lo mas ominoso de todo , el modelo sugiere que con condiciones similares a la del Pleistoceno , un colapso de WAIS , podría darse en escalas de tiempo de
DECADAS y no SIGLOS , como mostraban anteriores estimaciones.
EAIS y WAIS
Fig. 2.
Schematic cross-sections of an ice sheet approaching cliff failure. Ice flow is from left to right, from grounded ice to floating shelf. M = surface liquid runoff into crevasses. C = calving. O = oceanic basal melt. F = deformational flow across the grounding line. Red arrows show possible grounding-line movement. (a) With substantial ice shelf, and shallow surface slopes in the grounding zone. (b) After strong warming (large M,C,O) with the shelf nearly removed but still allowing shallow slopes. (c) With the shelf completely removed, exposing a vertical cliff > ∼100 m above sea level that undergoes structural failure, causing very rapid grounding-line retreat. Note that “cliff” failure can also occur at grounding lines with ice shelves, if the ice shelf provides little or no buttressing. It can occur in shallower depths than shown if the ice column at the grounding line is weakened by melt-driven hydrofracturing M (see text).
Fig. 3.
Ice distributions in a warm-climate simulation. The simulation starts from modern conditions, with a step-function change to a generic past warm climate applied at year 0. Atmospheric temperatures and precipitation are from a Regional Climate Model simulation with hot austral summer orbit, CO2 = 400 ppmv, and ocean temperatures are increased uniformly by 2 °C above modern. Color scale: Grounded ice elevations, m. Pink scale: floating ice thicknesses, m. The run is initialized from a previous simulation equilibrated to modern climate (panel (a), 0 yr). Both new mechanisms (cliff failure and melt-driven hydrofracturing) are active.
Fig. 4.
Global mean equivalent sea level rise in warm-climate simulations. Time series of global mean sea level rise above modern are shown, implied by reduced Antarctic ice volumes. The calculation takes into account the lesser effect of melting ice that is originally grounded below sea level. Cyan: with neither cliff failure nor melt-driven hydrofracturing active. Blue: with cliff failure active. Green: with melt-driven hydrofracturing active. Red: with both these mechanisms active. Geographic ice distributions for the latter run are shown in Fig. 3, and for the other runs in Fig. 5.AbstractGeological data indicate that global mean sea level has fluctuated on 103 to 106 yr time scales during the last ∼25 million years,
at times reaching 20 m or more above modern. If correct,
this implies substantial variations in the size of the East Antarctic Ice Sheet (EAIS). However,
most climate and ice sheet models have not been able to simulate significant EAIS retreat from continental size, given that atmospheric CO2 levels were relatively low throughout this period. Here, we use a continental ice sheet model to show that mechanisms based on recent observations and analysis
have the potential to resolve this model–data conflict. In response to atmospheric and ocean temperatures typical of past warm periods, floating ice shelves may be drastically reduced or removed completely by increased oceanic melting, and by hydrofracturing due to surface melt draining into crevasses. Ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing, and may fail structurally if stresses exceed the ice yield strength, producing rapid retreat. Incorporating these mechanisms in our ice-sheet model
accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales, and also causes retreat into major East Antarctic subglacial basins, producing ∼17 m global sea-level rise within a few thousand years. The mechanisms are highly parameterized and should be tested by further process studies.
But if accurate, they offer one explanation for past sea-level high stands, and suggest that Antarctica may be more vulnerable to warm climates than in most previous studies.Para , resumir , esto significa que para finales del siglo WAIS va a colapsar , y vamos a quedar bajo mas de 3-4 mts de agua , y sin contar la contribución de Groenlandia..
Posiblemente NO..Significa que las estimaciones que hasta ahora se han echo y que sugerían niveles del mar menores a 1mts para fines de este siglo, están
LARGAMENTE SUBESTIMADAS ,
Muy Probablemente ,SI
1294 Respuestas
629276 Vistas