A new analysis has revealed that apparent increases in Northern Hemisphere autumn snow cover were an illusion caused by improvements in satellite technology. In reality, snow cover has been shrinking by about half a million square kilometers per decade. This finding corrects long-standing data from the U.S. National Oceanic and Atmospheric Administration and highlights the role of snow in climate feedback mechanisms.
For decades, the Intergovernmental Panel on Climate Change has relied on climate records, including NOAA's measurements of autumn snow cover in the Northern Hemisphere since the 1960s, to inform global warming policies. These records initially suggested an increase of about 1.5 million square kilometers per decade in snow extent, an unexpected trend amid rising temperatures.
However, researchers led by Aleksandra Elias Chereque, a PhD student in the University of Toronto's Department of Physics, re-examined the data and found the opposite. Their study, published in Science Advances, attributes the perceived growth to evolving satellite instruments that became more adept at detecting thin snow layers over time. "It's as if the satellite's 'eye glasses' got better and better over that period," Elias Chereque explained. "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.'"
Snow cover is crucial for regulating Earth's temperature, reflecting about 80 percent of incoming solar energy compared to less than 50 percent from bare ground or vegetation. Its decline triggers the snow-albedo effect, where reduced reflectivity leads to greater heat absorption and further melting, contributing to Arctic amplification. Elias Chereque noted, "Snow cover is important because it's a positive climate feedback mechanism." The revised analysis confirms year-round snow loss driven by human-induced warming, enhancing understanding of climate models and future projections. Co-authors include Paul Kushner from the University of Toronto and researchers from Environment and Climate Change Canada.