Observations: Cryosphere
Cryosphere: the components of the Earth System that contain a
substantial fraction of water in the frozen state
The cryosphere comprises several components: snow, river and lake
ice; sea ice; ice sheets, ice shelves, glaciers and ice caps; and frozen
ground which exist, both on land and beneath the oceans
Clouds in the Arctic
• The Arctic is a very cloudy
place, with annually
averaged cloud cover of
70% or more
• The autumn is the cloudiest
season, while late winter is
the least cloudy season
• Until recently, satellites and
models tended to
underestimate the
cloudiness in the Arctic
Surface Observations
Satellite Estimates
Curry et al. (1996: J. Climate)
CALIPSO and ICESat: Cloud Cover vs
Sea Ice Fraction in October
Palm et al. (2010: JGR)
ICESat Cloud Optical Depth in October
2003-2007
More Open Water
Over water
Thicker Clouds?
Over ice
Rad.Heating of the
Surface?
Palm et al. (2010: JGR)
Simulated 21st Century Changes in Low
Cloud Amount and Sea Ice Extent
Vavrus et al. (2010: Clim.Dyn.)
ICE SHEETS
Topography in Greenland and Antarctica
Causes of Changes in Ice Sheets – In
General
Climate Forcing
• Surface Temperature
• Snowfall
• Ocean Thermal Forcing
•
•
•
•
•
Ice Sheet Processes
Basal Lubrication
Cryo-Hydrologic Warming
Ice Shelf Buttressing
Ice-Ocean Interaction
Iceberg Calving
Rapid Ice Sheet Changes – Reversible?
• Changes that are of
sufficient speed and
magnitude to impact on the
mass budget and hence rate
of sea level rise on time
scales of several decades or
shorter
• A further consideration is
whether and under what
circumstances any such
changes are ‘irreversible’,
i.e., would take several
decades to centuries to
reverse under a different
climate forcing.
• Example: Loss of a
significant fraction of the
Greenland ice sheet,
because at its new lower
elevation, the ice sheet
would only very slowly grow
thicker even in a cooler
climate
Supraglacial Lakes on the
Greenland Ice Sheet
July 2006
Photo: Joughin/UW Polar Science Center
The Greenland Ice Sheet is melting at
an accelerated rate
Steffen, K. et al. 2004. Geophys. Res. Lett.
Hanna, H. et al. 2005. Journal of Geophysical Research.
Photo: Roger J. Braithwaite, UK.
Accelerating changes in Greenland
• Surface melt that becomes runoff is a major
contributor to mass loss from the Greenland ice
sheet, which results in a lower (hence warmer)
ice sheet surface and a lower surface albedo
(allowing the surface to absorb more solar
radiation); both processes further increase melt.
• The warm summers of the last two decades, and
especially in 2012 are unusual in the multicentennial record
Low-lying ice sheets
• Regions of ice sheets that are grounded well
below sea level are most likely to experience
rapid ice mass loss, especially if the supply of
heat to the ice margin increases
• The Amundsen Sea sector of West Antarctica
is grounded significantly below sea level and is
the region of Antarctica changing most rapidly
at present.
The Collapse of Larsen A, B and C ice
shelfs in Antarctica
• Larsen A collapsed in
1995
• Larsen B collapsed in
2002
• Larsen C is now about
to collapse (2015)
• Larsen C is 10% larger
than Denmark!
• Why is this happening?
Rapid Ice Sheet Changes
• Collapse of floating ice shelves on the Antarctic
Peninsula, such as the 2002 collapse of the Larsen
B Ice Shelf which is unprecedented in the last
10,000 years, has resulted in speed up of
tributary glaciers by 300 to 800%
• Even if iceberg calving was to cease entirely,
regrowth of the Larsen B ice shelf to its precollapse state would take centuries based on the
ice-shelf speed and size prior to its collapse
Why is Larsen C collapsing now?
• The Antarctic Peninsula has warmed by 2.5°C
in the past 50 years.
• The ocean below Larsen C has warmed in
recent years up to - 2°C. That is warm enough
to melt ice
• The ice has been thinning from below by 28
cm per year for the past 15 years
• Larsen C is also melting from the top at a rate
of 4 cm per year
http://www.scientificamerican.com/article/massive-antarctic-ice-shelf-faces-imminent-risk-of-collapse/
The Greenland Ice Sheet
(Note different time
periods in a), b), c)!)
Mean
Surface
Mass
Balance
1989-2004
Ice Sheet
Velocity
2007-2009
Change in
Ice Sheet
Surface
Elevation
2003-2008
Evolution of Ice Loss 2003-2012
The Antarctic Ice Sheet
Mean Surface
Mass Balance
1989-2004
Ice Sheet
Velocity
2007-2009
Change in Ice Sheet
Surface Elevation
2003-2008
Evolution of Ice Loss 2003-2012
Cumulative Ice Mass Loss from
Greenland last 20 years
Cumulative Ice Mass Loss from
Antarctica last 20 years
Greenland and Antarctica compared
Rate of Ice Sheet Loss
SEASONAL SNOW
Northern Hemisphere Snow Cover
Decreases of:
- 0.8% per decade 1922-2012
- 1.6% per decade 1967-2012
- 2.2% per decade 1979-2012
Trends in Northern Hemisphere Snow
Cover in 106 km2 / decade
Largest negative trend in June, followed by May
Positive trends in December and November
Why?
In what month is the snow albedo feedback largest?
NH Snow Cover vs 40°N-60°N Land Air
Temperature in April
r = - 0.76
Black dots: Years 19672008
Red dots: Years 20002012
Snow cover trends in different regions,
different datasets
Northern Eurasia
Why are there often
positive trends at high
elevation and negative
at low elevation?
FROZEN
GROUND
Ground Temperature at 10 – 20 m
depth: Thawing of permafrost
A ticking climate bomb? Methane
from Siberian permafrost
Measurement sites
Abnormally high methane
concentrations found in this region
Shakhova et al. (2010: Science)
What happens if methane is released on a
massive scale from Siberian permafrost?
Feedback
processes that
significantly
amplify the
climate forcing
Release from
permafrost
Isaksen et al. (2011: GBC)
Permafrost Temperatures
Seasonally Frozen Ground
Seasonally Frozen Depth in Russia
Synthesis
Glacier Melting and Sea Level Change
How is this
likely to
evolve over
the next few
decades?