Factors influencing the Region’s values
Figure 6.7 Cyclonic wind (2005–2013) and flood plume (1991–2010) exposure
The cluster of severe cyclones and flood events in recent years has significantly affected the condition of many Great Barrier Reef habitats and species. Winds shown are those associated with category 4 and 5 cyclones. The likelihood of flood plume exposure (brown areas) is a cumulative assessment of multiple flood plumes based on remotely sensed conditions at the sea surface. The flood plume extent for 2010–11 (brown line) indicates the distribution of the flood plume as a result of the extreme weather events experienced over that summer. Source: Bureau of Meteorology 2013 57 (cyclones) and Devlin et al. 201158 (flood plume exposure)
Across Australia, heavy rainfall events and associated flooding are likely to become more frequent as air temperatures increase. 37 In northern Australia average monsoon rainfall may increase. 55 There will be a tendency for more large freshwater inflows to the marine environment. Rainfall is likely to become more variable, and the direction and magnitude of change in eastern and northern Australia remains a key uncertainty. 55 The El Niño–Southern Oscillation is the most important driver of natural climate variability in the Region and is likely to remain so. 55,62,63,64 Extreme El Niño events occurred during 1982–83 and 1997–98 with widespread coral bleaching observed.64,65,66,67 There is no consensus on observed long-term changes in the El Niño–Southern Oscillation, and low confidence in projected change in its variability. 55 Extreme El Niño occurrences are projected to increase. 38
6.3.2 Vulnerability of the ecosystem to climate change
Current and future climate change related threats to the Region’s ecosystem include sea temperature increases, altered ocean currents, changed weather patterns, ocean acidification and sea level rise. Potential effects for populations of species and groups of species and habitats are considered in many recent scientific studies. 34,68,69,70,71,72 The effects, both individually and combined, are likely to have far-reaching consequences for the Region’s ecosystem and its outstanding universal value as a world heritage area. The 2013 water quality scientific consensus statement73 concluded that ‘key Great Barrier Reef ecosystems are showing declining trends in condition due to continuing poor water quality, cumulative impacts of climate change and increasing intensity of extreme events’. For most ecosystem values, knowledge regarding the range and extent of impacts is limited, but growing steadily. However, the projected vulnerability of a number of the Region’s habitats and species indicates not all components are affected equally.72 Corals and seabirds are considered to be some of the most vulnerable species68,71,72,74 — both key attributes of the area’s outstanding universal value.