Background Information

Extreme events and climate change

Recent extreme events in ocean climate provide a glimpse of how future climate change could impact biodiversity, and human goods and services that our oceans provide.

Extreme events also help us develop and test adaptation responses and preparedness. The intense La Niña event in the summer of 2010/2011 led to two events in Australia that are likely to intensify in the future. One event was the extreme rainfall and floods in Queensland. These led to declines in seagrass beds, particularly for shallow sub-tidal species, because of increased nutrient loads and reduced light availability associated with sediment transport down rivers. Many green turtles died because of malnutrition, unable to find sufficient seagrass to meet their dietary requirements. Ongoing monitoring of turtle populations has shown these mortalities declined as water quality and seagrass beds recovered, but also as animals moved away from affected areas This event highlighted some of the impacts that can be expected from heavy rainfall events in the future. See 2012 Reports on El Niño-Southern Oscillation and Marine Reptiles for further information.

The second noteworthy event of 2010/2011 was the marine heatwave in Western Australia. The strong La Niña conditions contributed to an acceleration of the southward-flowing, warm-water Leeuwin Current, coupled with atmospheric conditions that transferred heat to the ocean. Coinciding with a period of calm weather in late February and early March 2011, caused extremely warm water temperatures, reaching 5°C above normal along the central west coast, Abrolhos Islands and Shark Bay. The hot water temperatures killed fish and invertebrates (e.g. Roei abalone) and temporary range extensions of many tropical species down the west coast and eastwards towards the Great Australian Bight, including whale sharks and manta rays that were sighted off Albany. Several fisheries and livelihoods were negatively impacted, but adaptation responses were put in place to maximize recovery. The abalone fishery in the northern region was shut, and a research trial started on the translocation of abalone from nearby unaffected areas into the depleted areas. This has been successful. The recruitment of juvenile scallops and crabs in Shark Bay was improving by the end of 2011, and the management focus is now is on the long-term recovery of the population. This event may also have longer-term implications for some marine stocks, as effects of the warm temperatures during their spawning and larval phases will take several years to manifest. Fisheries management already has approaches in place to deal with variability in the size of fish stocks, but modification of existing approaches and development of innovative new ones will be necessary in the future. It is likely that Australia will encounter such ocean heatwave conditions and extreme rainfall events much more frequently in the future (Fig. 1). See 2012 Reports on Leeuwin Current, Temperature, Macroalgae, Pelagic fish, and Seabirds for further information.



Figure 1. The effect of changes in temperature distribution on extremes. Different changes in temperature distributions between present and future climate and their effects on extreme values of the distributions:
(a) effects of a simple shift of the entire distribution toward a warmer climate;
(b) effects of an increase in temperature variability with no shift in the mean;
(c) effects of an altered shape of the distribution, in this example a change in asymmetry toward the hotter part of the distribution.
(Reproduced from Special Report of the IPCC: Managing the risks of extreme events and disasters to advance climate adaptation. Summary for Policy Makers).

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