24 fewer days of winter ice
The winter ice season is now 24 days shorter than it was in 1950 as Arctic lakes are freezing up later in the year and thawing earlier, according to a new study. The University of Waterloo research, sponsored by the European Space Agency (ESA), also reveals that climate change has dramatically affected the thickness of lake ice at the coldest point in the season. In 2011, Arctic lake ice was up to 38 centimeters thinner than it was in 1950.
"We've found that the thickness of the ice has decreased tremendously in response to climate warming in the region," said lead author Cristina Surdu, a PhD student of Professor Claude Duguay in Waterloo’s Department of Geography and Environmental Management.
"When we saw the actual numbers we were shocked at how dramatic the change has been. It's basically more than a foot of ice by the end of winter." The study of more than 400 lakes of the North Slope of Alaska, is the first time researchers have been able to document the magnitude of lake-ice changes in the region over such a long period of time.
"Prior to starting our analysis, we were expecting to find a decline in ice thickness and grounded ice based on our examination of temperature and precipitation records of the past five decades from the Barrow meteorological station," said Surdu. "At the end of the analysis, when looking at trend analysis results, we were stunned to observe such a dramatic ice decline during a period of only 20 years."
The research team used satellite radar imagery from ESA to determine that 62 per cent of the lakes in the region froze to the bottom in 1992. By 2011, only 26 per cent of lakes froze down to the bed, or bottom of the lake. Overall, there was a 22 per cent reduction in what the researchers call "grounded ice" from 1992 to 2011.
Researchers were able to tell the difference between a fully frozen lake and one that had not completely frozen to the bottom, because satellite radar signals behave very differently, depending on presence or absence of water underneath the ice.
Radar signals are absorbed into the sediment under the lake when it is frozen to the bottom. However, when there is water under the ice with bubbles, the beam bounces back strongly towards the radar system. Therefore, lakes that are completely frozen show up on satellite images as very dark while those that are not frozen to the lake bed are bright.
Read more at ENN affiliate Click Green.
Thin lake ice image via Shutterstock.