Sea ice presentation Mar 2008 .

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Transcript Sea ice presentation Mar 2008 .

Southern Hemisphere sea
ice versus climate change
A greater extent of sea
ice isn’t necessarily
inconsistent with the
current climate change
Hansard House of Representatives, 18th Feb 2008
“I have no doubt that all the anthropogenic global
warming believers have heard about the melting Arctic
sea ice, although interestingly we now hear Denmark’s
Meteorological Institute state that the ice between
Canada and south-west Greenland right now has reached
its greatest extent in 15 years.
It also noted that the Arctic sea ice extent has now
completely recovered. But, interestingly, how many
have heard that the extent of Antarctic sea ice is the
greatest measured since measurements began in 1979?”
Some definitions:
1.Sea ice concentration
2.Sea ice extent
3.Sea ice area
Pre 1973:
• Proxy data for regional sea ice extent
• Based on relationship between
methanesulphonic acid (MSA) and sea ice
• Digitised from hand drawn charts produced
in part from satellite observations
• Gridded onto 1o area grid
October 1978 onwards:
• Satellite data (Nimbus-7 SMMR and DMSP SSM/I
Passive Microwave)
• 25km resolution
The offending month…
September 2007
Southern Hemisphere
sea ice
Data from
Nimbus-7 SMMR and DMSP
SSM/I Passive Microwave
Extent: 19.2 million square kilometres
Area: 15.2 million square kilometres
Extent: 19.2 million square kilometres
Area: 15.2 million square kilometres
Extent anomaly:
• 3% above the long term mean
• 2nd highest on record (behind
Area anomaly:
• 6% above the long term mean
• highest on record
Reynolds’ SST
anomalies (NOAA
OI SST Analysis)
September 2006
the greatest
sea ice extent
since satellite records
began (1979)
(just to show it’s
not all clear cut)
Trends in Southern Hemisphere
sea ice
There are two classic views on Antarctic sea
ice extent changes with a warming climate:
1. Decrease
2. Increase
Something that stuck in my mind
Surface temperature
Zonal wind
Trends in zonal sea ice extent
since 1979…
Satellite data (Nimbus-7
Passive Microwave)
NSIDC – sea ice index
October 1978 through
to present day
Trends in sea ice concentration
since 1979…
Satellite data (Nimbus-7
Passive Microwave)
October 1978 through to
present day
All trends at 95% confidence
Longer term zonal trends
HadISST dataset:
- Monthly 1° grids of Dec
coverage for
- Based on only 2 days of satellite
1870 to present
data (1st and 2nd Dec)
- 6 previous months and 6 following
were all close to or well
below the long term mean
- A blend of In situ
observations and SSMI
- Anomalies based on 1973 through 2006
NSIDS sea ice index:
- Monthly 25km grids of ice coverage for
Oct 1978 to present
- SMMR and SSM/I instruments
- Anomalies based on 1979 through 2006
Jan 2008 (1.7)
Dec 2007 (1.5)
Feb 2008 (0.7)
Even longer term zonal trends
Ice core proxies
Ice Core Proxy
Ice Core Proxy
Law Dome MSA concentrations have a maximum positive
correlation to sea ice extent between 80-140E for Aug, Sep & Oct
Causes of change in Southern
Hemisphere sea ice
• Appears to be a link between total column
ozone and the SAM
• Subsequent link between the SAM and sea
ice in summer-autumn
Thompson, D.W.J., and S. Solomon, 2002:
Interpretation of recent Southern Hemisphere
climate change. Science, 296, 895-899.
December - May
“The mechanism linking tropospheric circulation changes
to stratospheric polar ozone changes is not well
“The ozone recovery through the C21 leads to a
warming of the polar stratosphere during spring,
stronger easterly zonal winds in the stratosphere during
late spring and early summer, and an increase of
tropospheric westerlies during summer.”
(NOAA) Perlwitz J., S. Pawson, R. Fogt, J. E. Nielsen, and W.
Neff, (2008): The impact of stratospheric ozone hole recovery
on Antarctic Climate. Geophys. Res. Lett., submitted.
“Antarctic sea ice extent continues to show
inter-annual variability and localized changes
but no statistically significant average trends,
consistent with the lack of warming reflected
in atmospheric temperatures averaged across
the region.”
IPCC, Climate Change 2007: The Physical Science Basis
Other views – CC Sceptic
“Conclusion: The data clearly show that Antarctica as a
whole is seeing increases in sea ice extent in recent
decades, in spite of what climate models suggest should
be occurring: steady warming. There are regional
differences, with Weddell Sea ice extent decreasing
and Ross Sea ice increasing, but overall the pattern is
clear: there is more ice, not less, surrounding
Antarctic Temperature and Sea Ice Trends over the Last
Century March 2006 – George Taylor (CECAP, International
Climate and Environmental Change Assessment Project)
Jan 2008
ACE CRC Antarctic Sea ice Issue Brief:
“In Antarctica, no discernable trends have been
documented for the continent as a whole, although there
have been noticeable decreases in sea ice extent around
the Antarctic Peninsula.
It is possible, however, that Antarctic sea ice may be
changing more in thickness than in extent. To date, there
are few broad-scale data about sea ice thickness and this
is a key area of research for the ACE CRC and others. In
addition, a summary of climate models from the
Intergovernmental Panel on Climate Change indicates that
sea ice extent in Antarctica will decrease in the future,
perhaps by as much as 50% by the end of the 21st
Since around 1980 the lack of overall warming in
the Antarctic has coincided with stable sea ice
on a Southern Ocean-wide scale, although there
have been significant regional variations.
However, Southern Hemisphere sea ice had a
short lived spike in coverage during the spring of
2007: during this period sea ice reached a new
record but has since returned to average levels.