Outstanding Questions in Recent Antarctic Climate Change and their Relevance to the Paleoclimate Record Dr. John Turner British Antarctic Survey Cambridge, UK

Antarctic Stations With Long In-situ Records Plus weather charts that we can trust from 1979

Near-Surface Temperature Changes – Full Records The greatest warming has been on the western side of the Antarctic Peninsula in winter and on the eastern side in summerThe greatest warming has been on the western side of the Antarctic Peninsula in winter and on the eastern side in summer

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 SAM

Mean sea level pressure trends /met/gjma/

Changes 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 on Surface Temperatures The contribution of the SAM to recent changes in surface temperature From Thompson and Solomon, 2002

Wind Changes Across the Peninsula Difference in ERA 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? The Ozone HoleThe Ozone Hole Increasing Greenhouse gasesIncreasing Greenhouse gases Natural variability– solar variability and volcanic activityNatural variability– solar variability and volcanic activity From Arblaster and Meehl (2006)

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

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

Tropical/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 Increasing The decrease of Arctic sea ice extent (percent per decade) Determined from Special Sensor Microwave/Imager satellite data Change of Antarctic sea ice extent (percent per decade)

The Spatial Pattern of Changes in Ice Concentration AnnualAutumn

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

Winter 500 hPa Temperature Trends

The Role of Polar Stratospheric Clouds The 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

Summary Even a short 50 year climate record shows complex variationsEven a short 50 year climate record shows complex variations But it is a time of marked human influence and separating natural from anthropogenic change is a major challengeBut it is a time of marked human influence and separating natural from anthropogenic change is a major challenge The eastern Peninsula summer warming is largely anthropogenicThe eastern Peninsula summer warming is largely anthropogenic 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 eastern Peninsula changeModels can reproduce some of the changes e.g. the eastern Peninsula change Models need to be used with great care since the atmosphere/ocean/ice interactions are so complexModels need to be used with great care since the atmosphere/ocean/ice interactions are so complex Higher horizontal resolution models are only part of the answerHigher horizontal resolution models are only part of the answer