To assess the risks to the Great Barrier Reef ecosystem posed by the 41 threats, the Australian Standard for risk assessment (AS/NZS 4360:2004) was followed. The best available information about the current state of the ecosystem, current use patterns, factors that are influencing the ecosystem, effectiveness of management and current resilience of the ecosystem was used (see Chapters 2-7).

Both the likelihood and consequence of each predicted threat were ranked on a five-point scale (see below). An overall risk level for each threat was then determined, based on both its likelihood and consequence.

It is important to note that such a risk assessment can only include those threats to the ecosystem that are known and identified. There is likely to be more unknown and unanticipated threats that have not been considered. Hence, the list of threats considered in subsequent Outlook Reports may be different.

Comprehensive risk analysis of an ecosystem the size and complexity of the Great Barrier Reef (recognising that each of the many threats affect the system over different time scales, at different intensities and with widely variable synergistic relationships) would be an undertaking well beyond the scope of this Report. Thus, several important broad assumptions were made to facilitate the assessment provided here:

• Each threat was initially assessed in isolation from others; compounding effects are discussed separately
• Each threat was assumed to be possible at any geographic location
• Threats were assessed as they are today (for example, current fishing catch amounts and techniques) or on the basis of documented trends (for example, trends in sea temperature and ocean acidification)
• Threats were assessed with existing, but not any future, management measures in place.
• It is important that the results below are interpreted with these assumptions in mind. 

• Likelihood and consequence categories for assessment

• Logic of assigning likelihood and consequence to individual threats