Southern Hemisphere sea ice versus climate change

A greater extent of sea ice isn’t necessarily inconsistent with the current climate change theory

Hansard House of Representatives, 18th Feb 2008 Dr JENSEN: “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 4.Volume

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 1 o 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 2 nd highest on record (behind 2006) 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)

There are two classic views on Antarctic sea ice extent changes with a warming climate: 1. Decrease 2. Increase Trends in Southern Hemisphere sea ice

Something that stuck in my mind Surface temperature MSLP Zonal wind speed

Trends in zonal sea ice extent since 1979…

Satellite data (Nimbus-7 SMMR and DMSP SSM/I Passive Microwave) NSIDC – sea ice index October 1978 through to present day

Trends in sea ice concentration since 1979…

Satellite data (Nimbus-7 SMMR and DMSP SSM/I Passive Microwave) NSIDC October 1978 through to present day All trends at 95% confidence

TRENDS IN JULY

TRENDS IN AUGUST

TRENDS IN SEPTEMBER

Longer term zonal trends

HadISST dataset: -Monthly 1° grids of ice coverage for 1870 to present -A blend of In situ sea surface observations and SSMI -Anomalies based on 1973 through 2006 Dec 1987: -Based on only 2 days of satellite data (1st and 2nd Dec) -6 previous months and 6 following months were all close to or well below the long term mean

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

Dec 2007 (1.5) Jan 2008 (1.7) Feb 2008 (0.7)

Even longer term zonal trends using Ice core proxies

Ice Core Proxy

Law Dome MSA concentrations have a maximum positive correlation to sea ice extent between E for Aug, Sep & Oct Ice Core Proxy

Causes of change in Southern Hemisphere sea ice

Ozone 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,

December - May

Ozone “The mechanism linking tropospheric circulation changes to stratospheric polar ozone changes is not well understood.” … “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.

The IPCC “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 Antarctica.” Antarctic Temperature and Sea Ice Trends over the Last Century March 2006 – George Taylor (CECAP, International Climate and Environmental Change Assessment Project)

Jan 2008

“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 century.” ACE CRC Antarctic Sea ice Issue Brief:

QTB 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.