Dr. Josefino Comiso

Dr. Josefino Comiso
Earth Sciences Directorate,
NASA/Goddard Space Flight Center
Ph. D. (University of California at L.A.)
Research Interest:
• the detection of climate change from
historical satellite and in situ data;
• polynyas, Odden, and bottom water
formation;
• air-sea-ice interactions and biological
processes in the polar regions;
• radiative transfer modeling studies and
satellite algorithms for sea ice and snow.
Observations of a Decreasing
Sea Ice Cover from Satellites
Josefino C. Comiso
Oceans and Ice Branch, Code 971
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Email: [email protected]
Arctic Forum
Washington, DC
13-14 May 2004
Scientific Motivation:
• The Arctic region is changing more rapidly than the rest of the
globe. Sea ice, snow cover, and glaciers are retreating,
permafrost is melting, and the Greenland ice sheet is thinning.
• The perennial ice cover is declining and must be monitored
since the demise of this ice cover would mean a change to a
seasonal Arctic ice cover. The impact of such a change can be
very profound
• Accurate pan-Arctic surface temperature data are needed to
understand where and how the Arctic is changing.
This talk updates of the following studies:
Comiso, J. C., A rapidly declining perennial ice cover, GRL, October, 2002.
Comiso, J. C., Warming in the Arctic from satellite clear sky observations,
J. Climate, November, 2003
Arctic Albedo and Ice Concentration during Spring
&Summer
• The passive
microwave and
visible data
provide
complementary
information.
• Both data
provides useful
and consistent
surface
information.
High Resolution
AMSR vs Landsat
• Higher spatial details can
be inferred from AMSR-E
than previous passive
microwave data,
especially at 89 GHz
• AMSR-E data at 6.25 km
resolution captures many
of the spatial features
from a high resolution
visible channel
• The 12.5 km data show
some details but the 25
km data smear out much
of the features.
Changes in the ice cover
during freeze-up from
October 1996 to 1998
• The Arctic basin is usually almost
all covered by the ice by middle of
October, as in October 12, 1996.
• The ice cover in October 1997 and
1998 shows substantial open water
areas indicating more melt and later
onset of freeze-up.
• Buoy and Sheba station data show
ocean warming and freshening
NH Monthly
averages of ice
extent, ice area
and ice
concentration
• Large seasonality and
interannual variability
• Trend towards low
concentrations or more
meltponding in the
summer.
Arctic Trends
1978–2001
• The hemispheric ice
extent is shown to be
declining at 2% per
decade while ice area
is declining at a
greater rate of 3% per
decade.
• Ice concentration is
declining partly
explaining the
difference in trend for
extent and area.
Regional
Trends in
Extents
• All trends are negative
except at the Bering
Sea where the extent
has been going up by
6.4 % per decade.
• Significant declines in
the other peripheral
seas are apparent.
• Three year running
mean show some
cyclical patterns in
some regions
Seasonal Trends
• Trends in extent are
all negative for all
seasons.
• Trends are most
negative in the
summer followed by
autumn.
• Trends are larger for
ice area than for ice
extent.
Yearly Ice
Concentration Maps of
the
Perennial
Ice Cover:
1979 to
2003
Yearly
Anomalies
of the
Perennial
Ice Cover:
1979 to
2003
Perennial Ice: Projection to 2075
Assuming a linear trend the ice cover in 2075 would be 75% less than that of the present
• .
Daily extents
and areas
during late
summer versus
long term
average
The perennial ice
cover in 2002 is
really the biggest
anomaly so far
Trends in the Perennial Ice (1979-2003)
1980
1990
2000
Twelve-year averages in the perennial ice
cover and decadal change map
• The actual area
changed by
about 12 % from
one period to the
other indicating a
10% decadal
change
• The 2003
perennial ice
cover follows the
same pattern as
those of the
previous 24
years
Last five year
average versus the
first five year
average in the time
series
Data shows some acceleration in
the decline of the perennial ice
cover
Area (1979-83) – 6.41 x 106 km2
Area (1999-2003) – 5.19 x 106 km2
Percentage diff: 19.3%
Comparison of
Temperature data
with Sheba and
Greenland Data
• Good agreement with
Sheba data with
sigma being 1.54K
• Good agreement with
Greenland station
data.
• Data are also
consistent with
POLES & Jones data
AVHRR vs
POLES Data
Surface temperatures
from three study
areas in the Arctic
where station data
are available are
compared.
The AVHRR GAC
data provides very
similar seasonal
fluctuations and
almost identical
trends.
AVHRR vs
Jones/Met
Station Data
None Arctic, high
temperature
data have been
enhanced to
be consistent with
meteorological
Data. New data set
shows better
agreement in all
regions, including
Europe and Asia.
Yearly Surface
Temperature
Averages (Aug-Jul)
The retrieved surface
temperatures in the
Arctic are shown to be
coherent from year to
year. The coldest
temperatures are
generally in Greenland,
followed by the Arctic
basin and Siberia.
While the patterns are
similar, they are slightly
different from one year
to another.
Yearly Surface
Temperature
Anomalies (Aug-Jul)
•The anomalies for each
year indicates that during
the 1980s the surface
temperatures were generally
low compared to the 1990s.
•It is apparent that cooling or
warming are not evenly
distributed throughout the
Arctic region.
•There are some areas of
large positive or negative
anomalies but these areas
move around from year to
year. The set of images
show a general warming
during the 22- year period.
Decadal
change in
Surface
Temperature
±
Trends (oC per decade):
NH
0.65 ± 0.12
Sea Ice
0.39 ± 0.15
Greenland 0.34 ± 0.28
Eurasia -0.28 ± 0.21
North Am 0.75 ± 0.22
Seasonal Trends
• Spring and
Autumn shows
the most positive
trends
• Winter data
shows
considerable
negative trend
• Summer trend is
in part
suppressed by
melt
temperatures
during this period
Length of the
Melt Season
• Trends are positive
in all areas except
Eurasia. In North
America the trend is
6 days per decade.
• Length of the melt
season is highly
variable, especially
over sea ice.
• Plots for North
America and sea ice
are similar.
Using Longer Arctic
Meteorological
Station data
• Station data show
0.08, 0.13, and 0.48
K/decade trends
during the last 100, 45,
and 20 years,
respectively.
• Trend is negative at
65 record length.
• Spectral analysis
shows 12 and 33 year
cyles.
Ice-Albedo-Ocean
Feedback
- An example of
some of the positive
feedbacks in the Arctic.
Other feedbacks could be
negative.
Some of the key
fluxes associated
With the Arctic
System
Summary and Conclusions
• The Arctic perennial ice cover appears to be
decreasing rapidly at 9 to 10% per decade while the
surface temperature has been increasing at 0.4 K per
decade over consolidated ice in summer. The multiyear ice cover might disappear within this century.
• The yearly anomalies in ice concentration are
predominantly positive in the 1980s and negative in
the 1990s. These results are consistent with yearly
anomalies in surface temperatures.
• Station temperature data show that the trend in Arctic
temperatures in the last 20 years is about 8 times
higher than that for the last 100 years. This is partly
because of warm periods in the 1930s. However,
modeling studies show that the rapid warming in
recent years is a reflection of a change in phase of the
Arctic Oscillation that is associated with enhanced
greenhouse gases in the atmosphere.
END OF PRESENTATION
Arctic Temperature
Trends and Errors
• Large warming trends are apparent
in North America and the Western
Arctic.
• Some cooling occurred in Russia
and the Bering Sea.
• Amplified Arctic trend appears to be
shifted to around 75oN and 90oW.
• The magnitude of the trend is not
correlated to the size of the
statistical error.
1980
Interdecadal
Change in the
perennial ice
cover
2003