One of those researchers, Stephen Déry, together with colleagues from the University of Northern British Columbia and Environment Canada, decided to update this study, to see what had changed in the past eight years.

"We were really surprised to find how quickly things are changing," Déry told environmentalresearchweb. "In just eight years, there has been a 28% increase in the area of snow cover that has retreated in June. This represents an acceleration in the snow-cover retreat when compared with the changes we assessed in the previous study."

Déry and his colleagues updated the research by including data up to September 2014 from the Rutgers University Global Snow Lab, and examining the effect of latitude and elevation on observed trends of weekly snow-cover extent in the Northern Hemisphere for the 43-year study period (1971–2014).

In the previous work, the researchers found that the maximum reduction of –4.63 × 106 km2 in snow-cover extent occurred at the beginning of June for the period between 1972 and 2006. But in this new study, which is published in Environmental Research Letters (ERL), the peak rate of change now occurs two weeks later, reaching a value of –6.46 × 106 km2. What's more, the reduction in snow-cover extent in the Northern Hemisphere is now 28.3% greater.

"This is a worrying trend because for many countries in the Northern Hemisphere, snow is an essential large seasonal source of water storage," said Déry.

The researchers found that the majority of statistically significant negative trends are in the mid-to-high latitudes, reaching a maximum reduction at 75.5°N. They also saw an elevation dependence of snow-cover extent over time. Statistically significant negative trends occur at most elevations, with the strongest observed at 3950 m above sea level.

"This acceleration pattern of the decrease in snow-cover extent was consistent across continents (i.e. Eurasia and North America), and suggests a common mechanism," said Déry. "While some climate-model studies have shown that the snow-albedo feedback may not be the main contributor to polar amplification, we believe our work reinforces our earlier conclusions that the snow-albedo feedback plays a leading role in the recent retreat of Northern Hemisphere snow cover."

Déry and his colleagues now want to pinpoint regional snow-cover trends in the Northern Hemisphere, to better understand the mechanism behind the snow-albedo feedback.

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