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PICTURE: THE PERCENTAGE OF EVERY SURFACE EXPERIENCE ANY POINT IN THE YEAR (1981-2010) OF ICE, SNOW, OR FROZEN GROUND. Show more CREDIT: PENG ET AL. (2021) THE FUTURE OF EARTH HTTPS://DOI.ORG/10.1029/2020EF001969
WASHINGTON – The global cryosphere – all areas of frozen water on Earth – shrank an average of about 87,000 square kilometers (about 33,000 square miles) per year between 1979 and 2016, an area about the size of Lake Superior climate change, according to a new study. This research is the first to provide a global estimate of the surface of the earth covered by sea ice, snow and frozen ground.
The extent of the land covered in frozen water is just as important as its mass, as its brilliant white surface is so effective at reflecting sunlight and cooling the planet. Changes in the size or location of ice and snow can change air temperatures, alter sea levels and even affect ocean currents around the world.
The new study has appeared in Earth’s Future, the AGU’s journal for interdisciplinary research on the past, present and future of our planet and its inhabitants.
“The cryosphere is one of the most sensitive climate indicators and the first to demonstrate a changing world,” said lead author Xiaoqing Peng, a physical geographer at Lanzhou University. “Its change in size represents a major global change and not a regional or local problem.”
The cryosphere contains nearly three-quarters of the world’s fresh water, and in some mountain regions, dwindling glaciers threaten drinking water supplies. Many scientists have individually documented shrinking ice sheets, dwindling snow cover and the loss of Arctic sea ice due to climate change. But no previous study has considered the total extent of the cryosphere above the earth’s surface and its response to rising temperatures.
Contraction in space and time
Peng and his co-authors from Lanzhou University calculated the daily extent of the cryosphere and averaged these values to produce annual estimates. As the size of the cryosphere grows and shrinks with the seasons, they found that the average area of the Earth’s cryosphere has shrunk overall since 1979, correlating with rising air temperatures.
The shrinkage occurred primarily in the northern hemisphere, with a loss of about 102,000 square kilometers (about 39,300 square miles), or about half the size of Kansas, per year. These losses are easily offset by growth in the southern hemisphere, where the cryosphere expands annually by approximately 14,000 square kilometers (5,400 square miles). This growth occurred primarily in the sea ice in the Ross Sea around Antarctica, likely due to wind and ocean currents and the addition of cold melt water from Antarctic ice sheets.
The estimates showed that not only did the global cryosphere shrink, but that many regions remained frozen for shorter periods of time. The average first day of frost is now about 3.6 days later than 1979, and the ice is thawing about 5.7 days earlier.
“This type of analysis is a nice idea for a global index or indicator of climate change,” says Shawn Marshall, a glaciologist at the University of Calgary who was not involved in the study. He believes a natural next step is to use this data to study when ice and snow cover gives the earth its greatest brightness, to see how changes in albedo on a seasonal or monthly basis affect the climate and how this changes over time.
In order to compile their global estimate of the extent of the cryosphere, the authors divided the surface of the planet into a grid system. They used existing data sets on global sea ice extent, snow cover, and frozen ground to classify each cell in the grid as part of the cryosphere if it contained at least one of the three components. They then estimated the extent of the cryosphere on a daily, monthly, and yearly basis and examined how it has changed over the 37 years of their study.
The authors say the global dataset can now be used to further study the effects of climate change on the cryosphere and how those changes affect ecosystems, carbon exchanges, and the timing of the life cycle of plants and animals.
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Notes for journalists:
Earth’s Future is an open access journal. Download a PDF copy of the paper here. Neither the paper nor this press release is embargoed.
Paper title:
“A holistic assessment of the global cryosphere expansion from 1979-2016”
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