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Antarctica and Global warming: some new findings

Antarctica and Global warming

Antarctica, the Great Heat Sink, acts as wheel against global warming. However, with ambivalent impact between the Antarctica and global warming, the condition has reached the break-even point, from where one is causing the other and the other is accelerating the first.

A recent study of Atmospheric Radiation Measurement West Antarctic Radiation Experiment (AWARE) has elaborated this point only to establish this complicated relationship.

Why Antarctica is considered a “Great Heat Sink”

  • Great Atmospheric circulations in the form of Hadley Cell in the Tropical belt, Ferrell Cell in the mid-latitude and Polar Cell in high latitude, connect Equator with Poles.
  • So, there is general movement of heat of Tropical belt towards poles through these dynamically linked atmospheric circulations.
  • Accumulated heat in the polar belt is radiated back to the space during their long winter period.
  • Among the two poles, it is the Antarctica that plays greater role in balancing thermal heat of Earth. This is mainly because Antarctica is the land mass with low specific heat capacity while Arctic is a water body with highest specific heat capacity. So, Antarctica loses heat at quite faster rate than that by Arctic.

Recent findings

  • AWARE experiments have found that with the global warming, polar region has become warmer, due to a change in Antarctic cloud properties.
  • AWARE is currently doing research work on changing Antarctic cloud properties and their impact on Antarctica warming. By Cloud properties we mean:
  1. How much of the cloud is comprised of ice particles versus liquid water drops (liquid water can exist in temperatures colder than -30 centigrade in very clean air),
  2. How much total water content is in the cloud,
  3. How the cloud is formed (e.g., from evaporation in the lower atmosphere, or being carried long-distance by moving air masses),
  4. How much solar radiation the cloud allows to reach the surface, and
  5. How much thermal radiation that the cloud radiates to warm the surface.
  • Warming Antarctica has changed the location of the boundary between the polar and Ferrell Cells.
  • It has also weakened the Southern Hemisphere Farrell cell, and allowed the Hadley Cell on the other side to strengthen, which in turn resulted in more rainfall due to increased latent heat release over Southern Hemisphere Tropical regions.
  • Moreover, global warming resulted in the slight southward shift of the storms and the intrusion of warm air which led to the breaking away of a large ice-shelf, thus enhancing the Antarctica warming.

What are the impacts of expanding Ferrell’s Cell?

An expanding Hadley cell resulting from global warming,

  • Results in the south ward extension of westerly wind
  • The pole ward shift of the westerly produces an intense (over 2oC) warming of subsurface coastal waters (between 200-700 m depth) of Antarctica.
  • However, this warming is also associated with
  1. A weakened Antarctic Slope Front (i.e., the boundary between cold, relatively fresh waters on the continental shelf and warmer, saltier waters found offshore),
  2. Weakened coastal currents, as well as
  3. Reduced shoreward Ekman transport in the surface layers (which maintains the cold fresh subsurface waters observed on the continental shelf). A pole ward wind shift decreases the onshore Ekman transport and decreases the associated Ekman pumping near the Antarctic coast. The across shore pressure gradients and the coastal current weaken, and the boundary between cold fresh water at the surface and warmer water below moves upward.
  • This allows warmer water to reach the continental shelf. The intrusions of warmer waters can cause increased melt rates at the base of floating ice shelves and a retreat of ice sheet grounding lines.
  • The increase of ice sheet discharge along the Antarctic coastal ocean can have strong ramifications for global sea level rise.

Why there is differential warming of Eastern and western Antarctica?

  • The circumpolar westerly prevents the warm air from the northern latitudes of the southern ocean from reaching the interior of eastern Antarctica.
  • This acts as insulator and makes eastern part a cold and isolated region.
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