https://www.theglobeandmail.com/canada/article-worlds-lake-ice-rapidly-shrinking-as-global-temperatures-climb-due-to/
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On thin ice: World’s lake cover shrinking as global temperatures climb
Jeff Lewis Environment Reporter
Published January 28, 2019
Melting ice roads threaten to cut off remote communities. Toxic algal
blooms are likely to spread. And games of winter shinny could disappear
within a generation.
The world’s lake ice is rapidly shrinking as global temperatures climb,
with potential to upend everything from seasonal transportation links
and recreation to the ecological health of tens of thousands of inland
waters, scientists said on Monday.
Climate change could see tens of thousands of lakes across scores of
countries in the Northern Hemisphere lose annual winter ice cover under
current warming trends, a study published in the journal Nature Climate
Change has found.
Even if the world’s industrialized countries limit warming to levels
agreed to in the Paris climate accord, the big thaw is likely to force
hundreds of millions of people to travel farther to reach lakes that
freeze each winter.
York University biologist Sapna Sharma led an international team of
researchers that predicts about 35,300 lakes stand to lose their annual
winter ice cover should worldwide temperatures increase by 2 degrees
Celsius above preindustrial levels.
That’s up from 14,800 lakes that currently experience intermittent ice
cover and could jump as high as 230,400 under the most extreme warming
scenarios. The retreat has major implications for anywhere from 394
million to 656 million people in more than 50 countries and shows that
impacts from climate change are not a distant threat, said Dr. Sharma,
an expert in environmental stressors on lakes and the study’s lead author.
Some regions in the northern United States, Sweden, Norway and Canada
are already seeing change. “We’re already experiencing these changes,”
she said in an interview.
"Lake Superior is no longer freezing every winter, and we’re sort of
getting these examples – these iconic lakes are beginning not to freeze
every year.”
To assess the threat of ice loss, Dr. Sharma and her colleagues built a
model using records for more than 500 lakes across the Northern
Hemisphere going back to 875 AD. That included 346 lakes in North
America, 136 lakes in Europe and 32 lakes in Asia.
They found that mean annual air temperature was the most important
factor for explaining ice cover, although lake depth, elevation and
shoreline complexity also played a role.
The model correctly predicted a lake’s susceptibility to loss of winter
ice cover 95 per cent of the time and was applied to a wider database of
1.4 million lakes to determine which ones would maintain annual ice
cover, assuming steadily rising global temperatures.
They found that 57,600, or 4.6 per cent, of ice-covered lakes in the
Northern Hemisphere could see intermittent winter ice cover under 3
degrees of warming.
That number falls to 35,300 if worldwide temperature increases are
limited to 2 degrees above preindustrial levels, as set out in the Paris
climate accord.
Conversely, the number of lakes that experience intermittent ice could
jump to 215,600 with little to no action to avert the worst effects of
climate change.
The numbers have big implications for water quality and quantity.
Years of reduced ice cover tend to coincide with warmer water
temperatures and lower oxygen concentrations that can kill fish and
increase the prevalence of toxic algal blooms.
Dr. Sharma said the results are likely conservative, partly because
they’re based on a subset of data; there are 117 million lakes globally,
and more than 50 million of those freeze, she said.
The temperature data also do not reflect the fact that northern regions
are warming more quickly than global averages, meaning those regions
could lose ice cover at a faster clip.
"It’s a really big problem for us culturally, to think about how we’re
going to adapt to this potential change and what does that mean for us
as a culture, and our sense of winter identity that we have,” she said.