A new study conducted by University of Toronto researchers has identified inaccuracies in historical Northern Hemisphere autumn snow cover data, impacting climate models used by the United Nations' Intergovernmental Panel on Climate Change (IPCC). Published in the journal Science Advances, the research revises previous observations from the U.S. National Oceanic and Atmospheric Administration (NOAA), indicating an actual decrease in snow cover over several decades, contrary to prior reports of an increase. This correction offers a refined understanding of Arctic warming dynamics and the snow-albedo effect.
Key Findings on Snow Cover Trends
The study's primary finding is a re-evaluation of Northern Hemisphere autumn snow cover trends. Historical data from NOAA, collected annually since the 1960s and incorporated into IPCC reports, had indicated an increase of approximately 1.5 million square kilometers per decade. However, the analysis conducted by University of Toronto PhD student Aleksandra Elias Chereque and her collaborators found that snow cover actually decreased by 0.5 million square kilometers per decade during the same period.
Cause of Data Discrepancy
This discrepancy was attributed to evolving instrumentation and data collection methods within the NOAA system. Over time, advancements in these methods led to an increased sensitivity to thin snow cover, which erroneously created the perception of greater overall snow extent. Climate scientists had previously raised concerns regarding the reliability of the NOAA data due to inconsistencies with other observations, concerns that this new analysis validated.
The Role of Snow in Climate
Snow cover is a critical climate metric due to its high reflectivity, known as albedo. It reflects approximately 80% of incoming solar energy back into space, significantly more than land and vegetation, which reflect less than 50%.
According to Elias Chereque, a reduction in snow cover decreases albedo, leading to increased energy absorption by the Earth's surface. This increased absorption can contribute to further snow loss, initiating a positive feedback loop. This process is a key component of 'Arctic amplification,' which describes the disproportionate rate of warming observed in the Arctic region compared to the global average.
Implications for Climate Science
The research, co-authored by atmospheric physicist Paul Kushner and collaborators from Environment and Climate Change Canada, reinforces existing evidence that snow cover is decreasing year-round.
Understanding these inaccuracies in historical snow cover data is expected to improve the comprehension of Arctic amplification, particularly the snow-albedo feedback mechanism influenced by anthropogenic warming. The corrected data also assists in the proper utilization of historical climate data, the estimation of future environmental trends, and the evaluation of climate model accuracy.