Are anthropogenic aerosols responsible for the northwest Australia summer rainfall increase? A CMIP3 perspective and implications

Cai, Wenju and Cowan, Tim and Sullivan, Arnold and Ribbe, Joachim and Shi, Ge (2011) Are anthropogenic aerosols responsible for the northwest Australia summer rainfall increase? A CMIP3 perspective and implications. Journal of Climate, 24 (10). pp. 2556-2564. ISSN 0894-8755

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Severe rainfall deficiencies have plagued southern and eastern Australian regions over the past decades, where the long-term rainfall is projected to decrease. By contrast, there has been an increase over northwest Australia (NWA) in austral summer, which, if continues, could be an important future water resource. If increasing anthropogenic aerosols contribute to the observed increasing summer rainfall trend, then as anthropogenic aerosols are projected to decrease what will the likely impact be on NWA summer rainfall? This study uses outputs from 24 climate models submitted to phase 3 of the Coupled Model Intercomparison Project (CMIP3) with a total of 75 experiments to provide a multi-model perspective. The authors find that none of the ensemble averages, either with both the direct and indirect anthropogenic aerosol effect (10 models, 32 experiments), or with only the direct effect (14 models, 43 experiments), simulate the observed NWA rainfall increase. Given this, it follows that a projected rainfall reduction is not due to a projected decline in future aerosol concentrations. The authors show that the projected NWA rainfall reduction is associated with an unrealistic and overly strong NWA rainfall teleconnection with El Nino-Southern Oscillation (ENSO). The unrealistic teleconnection is primarily caused by a model Equatorial Pacific cold tongue that extends too far into the western Pacific, with the ascending branch of the Walker circulation situated too far west, exerting an influence on rainfall over NWA rather than over northeast Australia. Models with a greater present-day ENSO amplitude produce a greater reduction in the Walker circulation and hence a greater reduction in NWA rainfall in a warming climate. Therefore, the cold bias and its impact represent a source of uncertainty for climate projections.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Accepted version deposited in accordance with the copyright policy of the publisher.
Faculty / Department / School: Historic - Faculty of Sciences - Department of Biological and Physical Sciences
Date Deposited: 16 Nov 2010 23:40
Last Modified: 19 Aug 2014 05:49
Uncontrolled Keywords: Australia; climate change; rainfall; models; IPCC; climate projections; ENSO; Walker circulation; Pacific cold tonque
Fields of Research : 04 Earth Sciences > 0401 Atmospheric Sciences > 040104 Climate Change Processes
04 Earth Sciences > 0401 Atmospheric Sciences > 040107 Meteorology
04 Earth Sciences > 0401 Atmospheric Sciences > 040101 Atmospheric Aerosols
Socio-Economic Objective: D Environment > 96 Environment > 9603 Climate and Climate Change > 960303 Climate Change Models
D Environment > 96 Environment > 9603 Climate and Climate Change > 960307 Effects of Climate Change and Variability on Australia (excl. Social Impacts)
Identification Number or DOI: 10.1175/2010JCLI3832.1

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