Outstanding Questions Outstanding Questions in Recent in Recent

Antarctic Climate Antarctic Climate Change and theirChange and theirRelevance to the Relevance to the

Paleoclimate RecordPaleoclimate RecordDr. John TurnerDr. John Turner

British Antarctic Survey British Antarctic Survey Cambridge, UKCambridge, UK

Antarctic Stations With Long In-situ Antarctic Stations With Long In-situ RecordsRecords

Plus weather charts that we can trust from 1979

Near-Surface Temperature Changes – Near-Surface Temperature Changes – Full RecordsFull Records

• The greatest The greatest warming has been warming has been on the western side on the western side of the Antarctic of the Antarctic Peninsula in winter Peninsula in winter and on the eastern and on the eastern side in summerside in summer

The Southern Annular Mode (SAM)The Southern Annular Mode (SAM)

• The principal mode of variability in the atmospheric circulation of the Southern Hemisphere (SH).

• Also known as the:• High Latitude Mode• Antarctic Oscillation

• Synchronous anomalies of opposite sign in Antarctica and the mid-latitudes: ‘see-saw’.

• Equivalent barotropic: revealed as the leading EOF in different atmospheric fields throughout the troposphere and lower stratosphere.

• Contributes a significant proportion of SH climate variability from daily to inter-annual timescales.

The Seasonal Trend in the The Seasonal Trend in the SAMSAM

Mean sea level pressuretrends1971-2000

www.bas.ac.uk/met/gjma/

Changes in the surface wind fieldChanges in the surface wind field

Approx. 15% increase in 850 hPa wind speed at Bellingshausen at the tip of the peninsula

Trends in the SAM and its Impact Trends in the SAM and its Impact on Surface Temperatureson Surface Temperatures

The contribution of the SAM to recent changes in surface temperature

From Thompson and Solomon, 2002

11

22

33

Wind Changes Across the PeninsulaWind Changes Across the Peninsula

Difference in ERA-40 10 m winds between strongly positive (1981, 1982, 2000) and strongly negative (1985, 1992) summer SAM.

1. Winds are passing over the northern Peninsula

2. Area of lee cyclogenesis

3. Poleward deflection of winds due to conservation of potential vorticity

Why Has The SAM Changed?Why Has The SAM Changed?

• The Ozone HoleThe Ozone Hole

• Increasing Greenhouse Increasing Greenhouse gasesgases

• Natural variabilityNatural variability– – solar variability and solar variability and volcanic activityvolcanic activity

From Arblaster and Meehl (2006)

The SAM QuestionsThe SAM Questions

1. How did the SAM change in the past under natural forcing? 2. What are the interactions of the SAM with other modes of

variability, such as ENSO?3. The SAM is influenced by greenhouse gas increases. Can

we see this signal in the pre-ozone hole ERA?4. How will the SAM change in the future during the ozone

recovery phase?

Winter Warming on the Western Winter Warming on the Western PeninsulaPeninsula

• The high correlation between The high correlation between Faraday temperature and ice Faraday temperature and ice extent over the Bellingshausen sea extent over the Bellingshausen sea suggests an increase in cyclonic suggests an increase in cyclonic activity since the 1950, but the activity since the 1950, but the reasons for this are not knownreasons for this are not known

Faraday Annual Mean Temperature

-9

-8

-7

-6

-5

-4

-3

-2

-1

020

01

19

98

19

95

19

92

19

89

19

86

19

83

19

80

19

77

19

74

19

71

19

68

19

65

19

62

19

59

19

56

19

53

19

50

19

47

-16

-14

-12

-10

-8

-6

-4

-2

0 1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

Tem

per

atu

re

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Mea

n i

ce c

on

cen

trat

ion

Temp Conc

Correlation of Faraday winter temperature and sea ice extent over the Bellingshausen sea

Western Peninsula Questions/IssuesWestern Peninsula Questions/Issues

1. We need evidence that there was more extensive sea ice in the Bellingshausen sea in the 1950s/60

2. Why was there more sea ice – weaker/fewer cyclones?3. Natural or anthropogenic?4. Can we find earlier examples of such marked decadal time

scale change?5. How far into West Antarctica do these summer/winter

change signals extend?6. Was there a tropical influence?

The Tropical InfluenceThe Tropical Influence

Rossby waves from the central pacific can influence the climate of West Antarctic and the Peninsula in particular

Tropical/Antarctic QuestionsTropical/Antarctic Questions

1. Why do very similar El Nino events produce such different extra-tropical responses?

2. How robust are the teleconnections?3. How do ENSO and the SAM interact? 4. Do we get different teleconnections via the atmosphere and

ocean?

Why is Antarctic Sea Ice Extent IncreasingWhy is Antarctic Sea Ice Extent Increasing

-8

-7

-6

-5

-4

-3

-2

-1

0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Per

cen

tag

e lo

ss

The decrease of Arctic sea ice extent (percent per decade)1979-2004

Determined from Special Sensor Microwave/Imager satellite data

Change of Antarctic sea ice extent (percent per decade)1979-2005

Total Ant Sea Ice Extent % Chnge/Dec Bootstrap

-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

1 2 3 4 5 6 7 8 9 10 11 12

The Spatial Pattern of Changes in Ice The Spatial Pattern of Changes in Ice ConcentrationConcentration

Annual Autumn

The Trend in Autumn MSLP 1979-2006 from the IPCC AR 4 Models The Trend in Autumn MSLP 1979-2006 from the IPCC AR 4 Models (Pa/year)(Pa/year)

Winter 500 hPa Temperature Winter 500 hPa Temperature TrendsTrends

The Role of Polar Stratospheric CloudsThe Role of Polar Stratospheric Clouds

Modelling results suggest that an increase in PSCs has the potential to significantly warm the troposphere

• PSCs forms at temperatures below about 190 K

• A cooling of the stratosphere is occurring worldwide, but it is particularly important in the Antarctic where the PSC threshold it being reached more frequently

• PSCs are not included in GCMs

SummarySummary• Even a short 50 year climate record shows complex Even a short 50 year climate record shows complex

variationsvariations• But it is a time of marked human influence and But it is a time of marked human influence and

separating natural from anthropogenic change is a separating natural from anthropogenic change is a major challengemajor challenge

• The eastern Peninsula summer warming is largely The eastern Peninsula summer warming is largely anthropogenicanthropogenic

• The western Peninsula winter warming is not understoodThe western Peninsula winter warming is not understood• Models can reproduce some of the changes e.g. the Models can reproduce some of the changes e.g. the

eastern Peninsula changeeastern Peninsula change• Models need to be used with great care since the Models need to be used with great care since the

atmosphere/ocean/ice interactions are so complexatmosphere/ocean/ice interactions are so complex• Higher horizontal resolution models are only part of the Higher horizontal resolution models are only part of the

answeranswer