1166th General Monthly Meeting

"The oceans and climate change"

Professor Matthew England, Climate and Environmental Dynamics Laboratory, School of Mathematics, University of NSW

Wednesday 5 November 2008, 6.30 for 7 pm
Conference Room 1, Darlington Centre, City Road

ABSTRACT

The oceans have always played a fundamental role in moderating global climate by transporting an excess of heat from the tropics to the poles. This occurs via global scale stationery eddies and a massive overturning of dense water at high latitudes. The oceans are also currently moderating climate change by absorbing massive amounts of heat and carbon. In addition, ocean circulation variations can have a profound impact on regional climate. Yet as the world's climate changes the moderating effect of the oceans will be dramatically reduced. In this talk I will outline the ocean's role in global mean climate and future climate change.

Other research directly relating to the oceans around Australia and the waters circling the Antarctic will also be explored. Twentieth century climate change has forced a poleward contraction of the Southern Hemisphere (SH) subpolar westerly winds. The implications of this wind shift for the ocean's thermohaline circulation (THC) is analyzed in models and, where available, observations. Substantial heat content anomalies can be linked to changes in the latitude and strength of the SH westerly winds. For example, the Southern Annular Mode projects onto sea surface temperature in a coordinated annular manner - with a conspiring of dynamic and thermodynamic processes yielding a strong SST signal. Subantarctic Mode Water (SAMW) change can be linked to fluctuations in the wind-driven Ekman transport of cool, low salinity water across the Subantarctic Front. Anomalies in air-sea heat fluxes and ice meltwater rates, in contrast, drive variability in Antarctic Surface Water, which is subducted along Antarctic Intermediate Water (AAIW) density layers. SAMW variations also spike T-S variability in AAIW, particularly in the southeast Pacific and southeast Indian Oceans. The location of zero wind stress curl in the SH can also control the distribution of overturning in the North Pacific / North Atlantic. A southward wind shift can force a stronger Atlantic THC and enhanced stratification in the North Pacific, whereas a northward shift leads to a significantly reduced Atlantic THC and the development of vigorous sinking in the North Pacific. This is because the distribution of wind stress over the Southern Ocean influences the surface salinity contrast between the Pacific and Atlantic basins. The implications of these findings for oceanic climate change are discussed.

BIOGRAPHICAL NOTES

Professor Matthew England is an Australian Research Council Federation Fellow and the Director of the UNSW Climate Change Research Centre (CCRC). England is a former Fulbright Scholar and winner of the Royal Society of Victoria Research Medal for 2007, two Eureka Prizes (Environmental Research 2006 and Land and Water 2008), the 2005 Priestley Medal and the Australian Academy of Science Frederick White Prize for 2004. He coordinated and led the 2007 Bali Climate Declaration by Scientists: a major international statement by the scientific community that specifies the reductions in greenhouse gas emissions required to minimise the risk of dangerous human-induced climate change (www.climate.unsw.edu.au/bali). He was a contributing author and reviewer of the Intergovernmental Panel on Climate Change (IPCC) Second and Third Assessment Reports. He is an expert in the ocean's role in regional climate variability and global climate change.

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