Significant decline of snow cover in the Northern hemisphere over the
last half century
Snow cover plays a major role in global energy balance, continental
thermal stability, and regional temperatures

Date:
June 29, 2023
Source:
University of California - Santa Cruz
Summary:
A new study that uses rigorous mathematical models and statistical
methods and finds declining snow cover in many parts of the northern
hemisphere over the last half century.


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FULL STORY ==========================================================================
In the face of the ongoing climate crisis, scientists from many fields
are directing their expertise at understanding how different climate
systems have changed and will continue to do so as climate change
progresses. Robert Lund, professor and department chair of statistics
at the UC Santa Cruz Baskin School of Engineering, collaborated on a new
study that uses rigorous mathematical models and statistical methods and
finds declining snow cover in many parts of the northern hemisphere over
the last half century.

Understanding snow cover trends is important because of the role that
snow plays in the global energy balance. Snow's high albedo -- the
ability to reflect light -- and insulating characteristics affects
surface temperatures on a regional scale and thermal stability on a continent-wide scale.

In the new study published in the Journal of Hydrometeorology,researchers analyzed snow cover data gathered from weekly satellite flyovers between
1967 (when satellites became more common) and 2021, which was divided into
grid sections for analysis. Of the grids that researchers determined had reliable data, they found that snow cover is declining in nearly twice
as many grids as it is advancing.

"In the Arctic regions, snow is going away more often than not -- I think climatologists sort of suspected this," Lund said. "But it's also going
away at the southern boundaries of the continents." In a study that took
about four years to complete, the researchers show that snow presence
in the Arctic and southern latitudes of the Northern hemisphere is
generally decreasing, while some areas such as Eastern Canada are seeing
an increase in snow cover. This could be due to increasing temperatures
in areas that are typically very cold but still below freezing, allowing
the atmosphere to hold more water, which then falls as snow.

Lund believes this is the first truly dependable analysis of snow cover
trends in the Northern hemisphere due to the rigor of the researchers' statistical methods. It is often challenging for non-statisticians
to extract trends from this type of satellite data, which comes as a
sequence of 0s or 1s to indicate if snow was present during a certain
week. The researchers also had to take correlation into account when
looking at trends, as the presence of snow cover one week greatly affects
the likelihood of snow cover the following week. These two factors were
taken into account with a Markov chain based model. Accurate uncertainty estimates of the trends could be computed from the model. The researchers
found hundreds of grids where snow cover was declining with at least
97.5% certainty.

However, they also found that some of the satellite data gathered in mountainous regions was unreliable, showing no snow in the winter and
several weeks of snow in the winter. This was likely due to a flaw in
the algorithm that processed the satellite data to determine if snow
was present or not.

"The reason this study took a lot of work is because the satellite data is
so doggone poor," Lund said. "Whatever the meteorologists did to estimate
snow from the pictures in some of the mountainous regions just didn't
work, so we had to take all the grids in the Northern hemisphere, and
figure out whether the data was even trustworthy or not." By determining
which satellite data is unreliable, this study can serve as a resource
to the scientific community who also may want to evaluate this snow
cover data for their research.

Lund collaborated on this study with UCSC Ph.D. candidate Jiajie Kong, Assistant Professor of Math and Statistics at the University of North
Florida Yisu Jia, Professor of Meteorology and Climatology at Mississippi
State University Jamie Dyer, Associate Professor of Statistics at
Mississippi State University Jonathan Woody, and Professor of Statistics
and Operations Research at the University of North Carolina at Chapel
Hill J. S. Marron. This research was supported by funding from the
National Science Foundation.

* RELATED_TOPICS
o Earth_&_Climate
# Snow_and_Avalanches # Climate # Severe_Weather #
Storms # Weather # Geography # Atmosphere # Global_Warming
* RELATED_TERMS
o Climate_model o Coriolis_effect o
Atmospheric_dispersion_modeling o Sea_level o Taiga o Snow o
Computer_simulation o Avalanche

========================================================================== Story Source: Materials provided by
University_of_California_-_Santa_Cruz. Original written by Emily
Cerf. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Yisu Jia, Robert Lund, Jiajie Kong, Jamie Dyer, Jonathan Woody,
J. S.

Marron. Trends in Northern Hemispheric Snow Presence. Journal of
Hydrometeorology, 2023; 24 (6): 1137 DOI: 10.1175/JHM-D-22-0182.1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/06/230629193256.htm

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