By C. Sasaki, U. of Toronto, Feb. 6, 2026
https://scitechdaily.com/why-scientists-are-rethinking-60-years-of-arctic-snow-data/
https://scitechdaily.com/why-scientists-are-rethinking-60-years-of-arctic-snow-data/
New research suggests that long-standing satellite records may have been quietly misleading scientists about Arctic snow cover. What once appeared to be a surprising increase turns out to be an illusion created by improving detection technology, masking a steady decline with major implications for Arctic warming.
Credit: Shutterstock
Decades of advances in satellite observation made it seem as though Arctic snow cover was growing, when in reality satellites were simply becoming better at detecting smaller and shrinking amounts of snow.
For many years, reports from the United Nations’ Intergovernmental Panel on Climate Change (IPCC) have summarized how Earth’s climate is changing.
New research from the University of Toronto, however, suggests that some of the data behind these assessments does not fully capture an important factor driving rapid warming in the Arctic.
Snow data shapes Arctic conclusions
IPCC assessments draw on many sources of climate information, including long-running records from the U.S. National Oceanic and Atmospheric Administration (NOAA) that track autumn snow cover in the Northern Hemisphere. Snow cover refers to how much land area is blanketed by snow, and these measurements have been collected every year since the 1960s.
Snow cover matters because it plays a major role in regulating Earth’s temperature. Snow reflects a large share of incoming energy back into space, while darker land surfaces and vegetation absorb much more heat. In general, snow reflects about 80 percent of incoming energy, compared with less than 50 percent for land and plants.
“Snow cover is important because it’s a positive climate feedback mechanism,” explains Aleksandra Elias Chereque, a PhD student in the department of physics in U of T’s Faculty of Arts & Science.
“This is referred to as the snow-albedo effect—albedo meaning reflectivity. Snow loss leads to a decrease in albedo, which leads to higher energy absorption, which, in turn, leads to enhanced snow loss. This is a contributing factor to a phenomenon known as ‘Arctic amplification,’ and it’s why we observe a disproportionate amount of heating in the Arctic.”
IPCC assessments draw on many sources of climate information, including long-running records from the U.S. National Oceanic and Atmospheric Administration (NOAA) that track autumn snow cover in the Northern Hemisphere. Snow cover refers to how much land area is blanketed by snow, and these measurements have been collected every year since the 1960s.
Snow cover matters because it plays a major role in regulating Earth’s temperature. Snow reflects a large share of incoming energy back into space, while darker land surfaces and vegetation absorb much more heat. In general, snow reflects about 80 percent of incoming energy, compared with less than 50 percent for land and plants.
“Snow cover is important because it’s a positive climate feedback mechanism,” explains Aleksandra Elias Chereque, a PhD student in the department of physics in U of T’s Faculty of Arts & Science.
“This is referred to as the snow-albedo effect—albedo meaning reflectivity. Snow loss leads to a decrease in albedo, which leads to higher energy absorption, which, in turn, leads to enhanced snow loss. This is a contributing factor to a phenomenon known as ‘Arctic amplification,’ and it’s why we observe a disproportionate amount of heating in the Arctic.”
Aleksandra Elias Chereque.
Credit: University of Toronto
A long-standing data discrepancy
Despite the importance of these measurements, scientists have questioned the reliability of the NOAA snow cover record for years. The trends suggested by the data did not align well with other observations, leading many researchers to warn that the results should be interpreted carefully.
Elias Chereque and her colleagues have now confirmed those concerns through a detailed reanalysis of the NOAA data. The original observations indicated that snow cover across the Northern Hemisphere increased by about 1.5 million square kilometers per decade, an area roughly one and a half times the size of Ontario.
The new analysis tells a very different story. Instead of growing, snow cover has been shrinking by about half a million square kilometers per decade, an area comparable to half the size of Canada’s most populous province.
A long-standing data discrepancy
Despite the importance of these measurements, scientists have questioned the reliability of the NOAA snow cover record for years. The trends suggested by the data did not align well with other observations, leading many researchers to warn that the results should be interpreted carefully.
Elias Chereque and her colleagues have now confirmed those concerns through a detailed reanalysis of the NOAA data. The original observations indicated that snow cover across the Northern Hemisphere increased by about 1.5 million square kilometers per decade, an area roughly one and a half times the size of Ontario.
The new analysis tells a very different story. Instead of growing, snow cover has been shrinking by about half a million square kilometers per decade, an area comparable to half the size of Canada’s most populous province.
Better satellites, misleading trends
Elias Chereque and her collaborators show that changes over the years in instrumentation and data collection methods in the NOAA data resulted in an increased sensitivity to thin snow cover and, thus, the erroneous observations that snow cover had increased.
“It’s as if the satellite’s ‘eyeglasses’ got better and better over that period,” says Elias Chereque. “It looks like there’s more snow now than there used to be – but that’s only because the satellite kept getting better ‘prescriptions for its glasses.’ It looked like there was more snow but that’s not what was happening.”
Elias Chereque and her collaborators show that changes over the years in instrumentation and data collection methods in the NOAA data resulted in an increased sensitivity to thin snow cover and, thus, the erroneous observations that snow cover had increased.
“It’s as if the satellite’s ‘eyeglasses’ got better and better over that period,” says Elias Chereque. “It looks like there’s more snow now than there used to be – but that’s only because the satellite kept getting better ‘prescriptions for its glasses.’ It looked like there was more snow but that’s not what was happening.”
Northern Hemisphere Snow and Ice Chart as of January 8, 2026.
Credit: NOAA
Correcting the record on Arctic warming
The study, published in the journal Science Advances, was co-authored by atmospheric physicist Paul Kushner, professor and chair in the department of physics and collaborators from the climate research division of Environment and Climate Change Canada. It adds evidence to the finding that snow cover is decreasing throughout the year and increases confidence in that result.
“We know snow loss is influenced by anthropogenic warming and snow loss also creates more potential for warming through the snow-albedo feedback, so we’ve gained a better understanding of this important mechanism of Arctic amplification,” Elias Chereque says.
“Showing how and why the snow cover trend was wrong helps us learn how to use this data set properly when we’re estimating past conditions and future trends. And that helps in understanding whether climate models are accurate.
“Developing tools like this helps us better understand climate and make better predictions about the future.”
Correcting the record on Arctic warming
The study, published in the journal Science Advances, was co-authored by atmospheric physicist Paul Kushner, professor and chair in the department of physics and collaborators from the climate research division of Environment and Climate Change Canada. It adds evidence to the finding that snow cover is decreasing throughout the year and increases confidence in that result.
“We know snow loss is influenced by anthropogenic warming and snow loss also creates more potential for warming through the snow-albedo feedback, so we’ve gained a better understanding of this important mechanism of Arctic amplification,” Elias Chereque says.
“Showing how and why the snow cover trend was wrong helps us learn how to use this data set properly when we’re estimating past conditions and future trends. And that helps in understanding whether climate models are accurate.
“Developing tools like this helps us better understand climate and make better predictions about the future.”
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