Beijing: The global cryosphere — all the areas with frozen water on Earth — shrank by about 87,000 square kilometers per year on average between 1979 and 2016, as a result of climate change, according to a new study.
The extent of land covered by frozen water is just as important as its mass because the bright white surface reflects sunlight so effectively, cooling the planet. Changes in the size or location of ice and snow can alter air temperatures, change the sea level, and even affect ocean currents worldwide.
The researchers from Lanzhou University in China calculated the daily extent of the cryosphere and averaged those values to come up with yearly estimates. While the extent of the cryosphere grows and shrinks with the seasons, they found that the average area covered by Earth’s cryosphere has contracted overall since 1979, correlating with rising air temperatures. The new study is published in Earth’s Future.
“The cryosphere is one of the most sensitive climate indicators and the first one to demonstrate a changing world,” said first author Xiaoqing Peng, a physical geographer at Lanzhou University. “Its change in size represents a major global change, rather than a regional or local issue.”
The shrinkage primarily occurred in the Northern Hemisphere, with a loss of about 102,000 square km each year. Those losses are offset slightly by growth in the Southern Hemisphere, where the cryosphere expanded by about 14,000 square kilometers annually. This growth mainly occurred in the sea ice in the Ross Sea around Antarctica, likely due to patterns of wind and ocean currents and the addition of cold meltwater from Antarctic ice sheets.
The estimates showed that not only was the global cryosphere shrinking but that many regions remained frozen for less time. The average first day of freezing now occurs about 3.6 days later than in 1979, and the ice thaws about 5.7 days earlier.