Snow-Cover Trends
(1967–2018):
A Comparison
between
Climate Models
and Observations
by
Ronan Connolly
Michael Connolly
Willie Soon
David R. Legates
Rodolfo Gustavo Cionco
Víctor M. Velasco Herrera
Center for Environmental Research
and Earth Sciences (CERES),
Salem, MA 01970, USA;
Published March 20, 2019
"Although several studies
have compared the observed
spring snow cover trends
to climate model predictions,
little direct comparison
of trends for other seasons
has been conducted.
Moreover, most of the
comparisons have focused
exclusively on linear trends,
while the observed trends
often show distinctly non-linear
fluctuations from year to year.
Therefore, in this paper,
we directly compare the
observed Northern Hemisphere
snow-cover trends
for all four seasons
( and annual trends )
to the CMIP5 climate model
hind-casted trends.
Our analysis compares
both the linear trends
( obtained by linear
least squares fitting )
and the time-series
themselves."
Actual observed changes
in Northern Hemisphere
snow cover, derived
from satellite records,
were compared to
predictions by
all available
Coupled Model
Inter-comparison
Project Phase 5
( “CMIP5” )
climate models,
over the duration
of the satellite records,
( 1967–2018 ).
There were 196
climate model simulations,
from 24 climate models.
A longer record (1922–2018 )
for the spring season, combining
ground-based measurements
with satellite measurements,
was also compared to model outputs.
The climate models predicted
snow cover would steadily
decrease for all four seasons.
That did NOT happen.
Only spring and summer
had a long-term decrease,
and the pattern observed
was quite different from
model predictions.
The observed trends
for autumn and winter
suggest a long-term
increase, although
not enough to be
statistically significant.
Changes in snow cover
are an important part
of global climate change.
Total snow cover is considered
a key indicator of climate change.
Climate models since the 1970s
consistently predicted
a significant, and continual,
decline in total snow cover.
Snow cover changes
can further contribute
to global warming,
by altering the
Earth’s surface albedo,
( how much sunlight
is reflected back to space ),
because white snow
reflects lots of sunlight,
while brown dirt does not.
Satellite snow cover observations
for the Northern Hemisphere
are available since November 1966,
from a joint project with the
National Oceanic and Atmospheric
Administration (NOAA) and the
Rutgers University Global Snow Lab.
Various ground-based
measurements of local snowfall
and snow cover extend back
prior to the pre-satellite era.
Brown and Robinson
combine these data sources
with the Rutgers dataset
to extend estimates of
Northern Hemisphere snow cover
for March and April back to 1922,
and to 1915 for North America.
Brown, R.D.; Robinson, D.A.
Northern Hemisphere spring snow cover
variability and change over 1922-2010
including an assessment of uncertainty.
Cryosphere 2011, 5, 219–229.
By averaging the two
monthly estimates,
they derived a combined
“spring” estimate.
Northern Hemisphere snow cover
has actually increased, making the
climate models look foolish,
as they always look, when
compared with reality:
Quotes from the 2018 report
of the Rutgers Snow Lab
are below:
https://climate.rutgers.edu/snowcover/files/Robinson_snowdata2018.pdf
"Annual snow cover extent (SCE)
over Northern Hemisphere (NH) lands
averaged 25.6 million square
kilometers in 2018.
This is 0.5 million sq. km. more
than the 49-year average
(mapping extends back to late 1967,
however several early years in the record
are incomplete),
and ranks 2018 as having
the 12th most extensive
(or 38th least extensive)
cover on record"
"This is 0.2 million sq. km. less
than the 2017 mean extent.
SCE over both NH continents,
including the Greenland ice sheet,
is considered in this analysis."