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  • Behind the Global Glacial Meltdown

  • Monday, 15th August 2016

Ice Age is a long period of low temperature conditions with glaciers covering many parts of the Earth. The period between Ice Ages is called "interglacial" which has a milder climate. The last Ice Age ended about 10,000 years ago. Since then, the Earth has entered into an interglacial period with a warmer climate, becoming more inhabitable for humans and favourable for civilization to flourish.

At the end of the last Ice Age, glaciers around the world started to melt and retreat. Owing to the uncertainty in the estimation of timing, it was difficult to tell for sure whether the glacier retreats in different parts of the world were synchronous. As such, the glacial meltdown was also attributed to regional factors such as changes in solar radiation, precipitation pattern and ocean circulation.

Scientists have recently re-examined more than 1000 boulders left behind by the retreating glaciers across the globe and applied an improved methodology to estimate the timing of glacier retreats[1,2]. The boulders, previously covered by the glaciers, would be exposed to the atmosphere and bombarded by cosmic rays, producing the radioactive isotope Beryllium-10. By analysing the level of the isotope, scientists were able to estimate the exposure age of the boulders and hence the time when the glaciers retreated. The results revealed that the retreat of glaciers across the globe was broadly synchronous with the rise of atmospheric concentration of carbon dioxide as derived from ice core analyses. Using climate model simulations, it was concluded that the primary cause of the global glacial meltdown was the rise of atmospheric concentration of carbon dioxide (Figure 1).

Figure 1

Figure 1      Scientists concluded that the primary cause of the global glacial meltdown at the end of the last Ice Age was the rise of atmospheric concentration of carbon dioxide. (Photo courtesy: Oregon State University)


It took about 7000 years for the concentration of carbon dioxide to rise from 180 ppm to 280 ppm near the end of the last Ice Age. Atmospheric concentration of carbon dioxide has been increasing since the Industrial Revolution, and it only took a century or so for the concentration to exceed 400 ppm (Figure 2). With the concentration of carbon dioxide keeps setting new records, should we not be worried about the accelerated melting of glaciers around the world and the subsequent sea level rise (Figure 3)?

Figure 2

Figure 2      Variation of atmospheric carbon dioxide concentration over the last 800,000 years. (Source: World Meteorological Organization)



Figure 3

Figure 3      Accelerated glacier retreat. (Source: "CHASING ICE")




F.C. Sham


References:

[1] As Ice Age ended, greenhouse gas rise was lead factor in melting of Earth's glaciers.
http://www.bc.edu/offices/pubaf/news/2015-jul-aug/ice-age-glaciers-melted-because-of-greenhouse-gas-increase.html?cq_ck=1440100083400

[2] Regional and global forcing of glacier retreat during the last deglaciation.
http://www.nature.com/ncomms/2015/150821/ncomms9059/full/ncomms9059.html



Last revision date: <06 Sep 2016>