C20C Workshop Trieste, Italy 19 – 23 April 2004 The impact of stratospheric ozone depletion and CO 2 on AAO trends and regional climate change at surface of Southern Hemisphere Syktus J., I. Smith 2, G. McKeon 1, M. Dix 2 & W. Cai 2 1 Department of Natural Resources, Mines and Energy, Brisbane, Australia 2 CSIRO Atmospheric Research, Melbourne, Australia

C20C Workshop Trieste, Italy 19 – 23 April 2004 – the source of observed 20thC trends in the SAM is a matter of scientific debate with stratospheric ozone losses, greenhouse gas increases and natural variability all possible players –my motivation is from practical point of view; does it influence regional climate trends and change – since it is difficult to separate the contribution of these various forcings in the observed record, a global climate model has been used Motivation

C20C Workshop Trieste, Italy 19 – 23 April 2004 Southern Hemisphere Annular Mode - Discussion It is a dominant mode of low frequency variation of the SH circulation. Characterized by zonally symmetric fluctuations in the extra-tropical atmospheric circulation that extends from surface to the stratosphere The observation show that AOO index has trend towards a positive values since the late 1970s, coincident with occurrence of ozone depletion (Marshall 2003) The issue here is whether AGCM forced with observed SST and radiative forcing factors such as CO 2 & O 3 can simulate the trends in surface MSLP and other surface characteristics at regional scales Climate models forced by changing CO 2 or by decreasing stratospheric ozone usually show a trend in the SH annular mode. Still an open question how good a representation of stratosphere is needed to accurately model tropospheric climate and climate change, however link to stratosphere is not essential for MSLP to have SH annular mode like response

C20C Workshop Trieste, Italy 19 – 23 April 2004 Martin Visbeck Todd Mitchell

C20C Workshop Trieste, Italy 19 – 23 April 2004 Problem and approach During the past decade large parts of eastern Australia experienced unprecedented and persisting drying trends Drying trends in eastern Australia in recent decades  Water supply restrictions in major cities of Eastern Australia Identification of possible forcing factors; GHG,O 3, land cover change … Limitations of the approach Review of the current state of knowledge Simulation results and discussion

C20C Workshop Trieste, Italy 19 – 23 April 2004 Rainfall Relative to Historical Records Australia– July 1992 to June 2003 Percentiles Red = Last 10 years are in the bottom 10% of all previous ten July to June year periods from 1890

C20C Workshop Trieste, Italy 19 – 23 April 2004 Trends in annual rainfall expressed in terms of the trend correlation coefficient (r, not b) to 2002 MJJASO 1952 to 2002 NDJFMA Annual

C20C Workshop Trieste, Italy 19 – 23 April 2004 (a)area-averaged total, mean=461 (b)area-averaged mean decile value r (SOI) =0.50 r (SOI) =0.44 All-Australian annual rainfall indices

C20C Workshop Trieste, Italy 19 – 23 April 2004 Despite 2002 being one of the driest years on record, Australia appears to have become wetter This positive trend in NW Aus appears because of relatively wet years in the second half of the record (e.g.1974, 2000). The chances of these trends arising due to random fluctuations of the data are about 5% We do not know: where the trends have occurred if there are any compensating negative trends which seasons are involved

C20C Workshop Trieste, Italy 19 – 23 April 2004 Second dominant EOT of Australian Observed Rainfall - S2 Central west (15%) S2 represents variability over that potion of the continent where rainfall stations are most sparse. It is possible that T2 may be dominated by the relatively small number of stations whose effect has been interpolated over large distances. (Smith 2004) NDJFMA T2 has also positive & statistically significant trend during the period, strongest over the past decade

C20C Workshop Trieste, Italy 19 – 23 April 2004 Summary Increases in all-Australian annual rainfall over the past 100 years are the result of increases in summer rainfall over much of the western half of the continent over the past 50 years. The magnitude and pattern of the increases appears unusual and unlikely to be the result of “natural variability”. It is not possible to describe winter rainfall trends as unusual. Increases in summer rainfall have been suggested as a response to increased greenhouse gases. Temperatures have risen substantially over both Australia and the Indian Ocean over recent decades. These may be linked to the rainfall changes. These may, in turn, be attributable to EGG - but earlier than expected.

C20C Workshop Trieste, Italy 19 – 23 April 2004

Forecast skill assessment (Goddard et al., 2004, BAMS) March 2002 Rainfall Forecast for July to September IRI Net Assessment Forecasts NR&M contributes NCEP model output at monthly intervals to IRI consensus forecast since late 1998

C20C Workshop Trieste, Italy 19 – 23 April 2004 Murray-Darling Basin – April-September rainfall and maximum temperature

C20C Workshop Trieste, Italy 19 – 23 April 2004 Water Storages Levels Gladstone and Gold Coast water restriction in place for number of years now. December: 21 NSW towns required water carting Canberra: First water restrictions since 1966 Melbourne: First water restrictions since 1982 Follows a 6-year dry spell in southern Australia Gladstone Gold Coast

C20C Workshop Trieste, Italy 19 – 23 April 2004 Natural Annual Flows into Hume Weir (MDBC) Lowest 4-year period on record Natural Annual Flows into Hume Weir (MDBC)

C20C Workshop Trieste, Italy 19 – 23 April 2004 CSIRO Mk3 AGCM Model Atmosphere Grid:T63 (1.88 o x 1.88 o ) 18 levels - hybrid ,p with top at 4.5 hPa (~ 36 km) Semi-Lagrangian moisture transport UKMO convection (Gregory & Rowntree) Liquid water clouds (Rotstayn) Land surface Soil model - 6 levels Temperature, water, ice 9 soil types 13 land surface and/or vegetation types Snow-cover model - 3 layers

C20C Workshop Trieste, Italy 19 – 23 April 2004 CSIRO T63/L18 C20C Experiments 5 runs: SST only 5 runs: SST and O 3 5 runs: SST only 5 runs: SST and solar 5 runs: SST, solar and CO 2 5 runs: SST, solar, CO 2 and O 3 10 runs: SST, solar, CO 2 and O 3 in progress

C20C Workshop Trieste, Italy 19 – 23 April 2004 Ozone scenario used in CSIRO AGCM simulations Observations

C20C Workshop Trieste, Italy 19 – 23 April 2004 Ozone recovery projections

C20C Workshop Trieste, Italy 19 – 23 April 2004 Trends in the Southern Hemisphere annular mode in CSIRO Mk2 transient greenhouse runs reverse when the forcing is stabilised. However, this may take several centuries to take place, depending on the emission scenario used.

C20C Workshop Trieste, Italy 19 – 23 April 2004 CSIRO Mk2 Model, Warming Run

C20C Workshop Trieste, Italy 19 – 23 April 2004 CSIRO Mk2 Model, greenhouse run, showing when the AAO goes up rainfall over SWWA decreases, and vice-versa! Correlation between the AAO and JJA Rainfall

C20C Workshop Trieste, Italy 19 – 23 April 2004 ANN MAM DJF JJA SON MSLP change in Mk 3

C20C Workshop Trieste, Italy 19 – 23 April 2004 SWWA RainfallSAM Winter Spring

C20C Workshop Trieste, Italy 19 – 23 April 2004 Queensland summer rainfall in GHG scenario with Mk3 coupled AGCM

C20C Workshop Trieste, Italy 19 – 23 April 2004 Model Simulated and NCEP R1 JJA MSLP for JJA

C20C Workshop Trieste, Italy 19 – 23 April 2004 Annual Trend NCEP PSL

C20C Workshop Trieste, Italy 19 – 23 April 2004 Model Simulated MSLP difference for JJA

C20C Workshop Trieste, Italy 19 – 23 April 2004 Model Simulated MSLP difference for JJA

C20C Workshop Trieste, Italy 19 – 23 April 2004 Model Simulated MSLP difference for JJA

C20C Workshop Trieste, Italy 19 – 23 April 2004 Model Simulated MSLP difference for JJA

C20C Workshop Trieste, Italy 19 – 23 April 2004 Model Simulated MSLP difference for JJA

C20C Workshop Trieste, Italy 19 – 23 April 2004 Trends in the SAM: impact on Antarctic temperatures   Time series of the SAM based on NCEP-NCAR Z850 data and Z500 Antarctic radiosonde data (Thompson & Solomon, 2002). Data are normal- ized to Source: Todd Mitchell ( Regression of Antarctic surface temperature anomalies vs unit change in the SAM, (Kwok & Comiso, 2002)

C20C Workshop Trieste, Italy 19 – 23 April 2004 Response of surface temperature Warming over Antarctic Peninsula and cooling over Eastern Antarctica seen in both CO 2 and O 3 forcing, but stronger in O 3

C20C Workshop Trieste, Italy 19 – 23 April 2004 Response of surface temperature DJF cooling over Eastern Australia due to CO 2 effect and an opposite effect when O 3 is added

C20C Workshop Trieste, Italy 19 – 23 April 2004 Response of precipitation NDJFM wetter over Eastern Australia due to CO 2 effect and an opposite effect when O 3 is added, follows from surface temperature changes in previous slide. SPCZ changes

C20C Workshop Trieste, Italy 19 – 23 April 2004 Response of JJA precipitation JJA weaker Asian monsoon due to CO 2 effect and an lesser effect when O 3 case is considered. The area of precipitation decrease/increase in Southern Ocean consistant with AAO trend is visible

C20C Workshop Trieste, Italy 19 – 23 April 2004 Summer Rainfall Difference between and Observed Difference SSTs only SSTs + Solar + CO 2 SSTs + Solar + CO 2 + Ozone

C20C Workshop Trieste, Italy 19 – 23 April 2004 Observed Difference SSTs only SSTs + Solar + CO 2 SSTs + Solar + CO 2 + Ozone Summer Rainfall Difference between and 1998/9-2000/1

C20C Workshop Trieste, Italy 19 – 23 April 2004 Conclusions Both CO 2 and O 3 forcing have contributed to pressure changes in Southern Hemisphere These changes are similar to SH Annular Mode The model has rather weak response to a radiative forcing when years long ensemble mean climatology climatology is compared Model show some systematic response in surface air temperature and precipitation, significance of which needs to be assessed At regional scale contribution of CO 2 and O 3 to simulated rainfall anomalies is positive