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South Curl Curl Beach, Sydney. Storm waves have exposed coastal protection works and ramp foundations. Photo taken 1/9/2015

Several years ago in the office of the Wentworth Group of Concerned Scientists, I was in a deep and meaningful discussion with colleague Tim Stubbs. Mr Stubbs, as he is affectionately called, challenged me to explain the interaction of present-day impacts of extreme events and the potential impacts of climate change on Australian environments and society. I was pondering a better way to communicate the challenges we face as a nation in not only adapting to conditions that will prevail as we move into the new climate era, but also how we can better minimise the impacts of natural disasters that we have endured in the past and were experiencing then (for instance, the millennial drought, with accompanying reduced river flows, bushfires and heat waves).

At the time some were pointing to the over emphasis on government funding for post-disaster recovery and not investing in pre-disaster planning, while others focussed on climate change adaptation, especially consideration of the impacts of sea level rise. How to bring all this together and offer a better way to communicate risk that communities face as a result of being vulnerable to extreme events now and those likely to be more extreme under uncertain climate change conditions in the future? This question was relevant to a talk I was about to give to an audience of climate change sceptics.

I knew the audience would be aware of past impacts of coastal storms including shoreline erosion, overwash and estuary floods. They had experienced the devastation of such events. It was easy for me to show images of damage to property and infrastructure as well as threats to life. There is no doubting Australia has a pre-history and a history of a range of different natural forces that have had dramatic impacts.

As population grows, many communities find themselves in harm’s way and vulnerable to a variety of natural hazards. To what extent will the level of vulnerability increase for those communities or sectors of the economy under climate change, and how could I best build on the understanding of current exposure to risk and highlight in talks the need to limit as best we can the potential of increased exposure due to climate change?

Mr Stubbs and I hit the white board! Thinking of risk in the conventional way as likelihood multiplied by consequence, Mr Stubbs and I, calling on our engineering and geomorphology backgrounds, summarised the nature of risk: V1 x V2 = Rn.

In this expression V1 encompasses vulnerability as seen from the historical record, including what has been documented in an area as having impacted communities and environments. It embraces extreme events as we know them and that are part of the natural variability of the climatic conditions for any given region. This variability can embrace inter-decadal shifts in conditions that are increasingly well known to climate scientists, and to those of us who have studied historic impacts of storms along the east coast of Australia. Understanding vulnerability to such extreme events is critical to coastal management and land use planning.

The term V2 takes the risk discussion a step further. It recognises that historically documented vulnerability can be exacerbated by forces resulting more directly from climate change. For example an increasing rate of sea level rise may amplify the extent of shoreline inundation and damage well beyond the historic records. Vulnerability also increases as storms change their intensity, duration or mode of attack upon any given stretch of coast. Increased sea temperature, sea water acidification, even prolonged droughts that may stretch for periods beyond those of known for an area, are all included in this term.

So while there are signals that climate change is underway, it is not easy to differentiate the impacts of such from natural variability as seen in historic times. That is why we brought the two components of vulnerability together in this expression.

Risk as defined by Rn opens up the opportunity to address future problems in coastal areas where we not only face extreme events now, but also the impact of similar if not more intense events in the future, for instance storm surges on higher sea levels. Solving the exponent n is a challenge because it reaches into the world of projections and probabilities.

Mr Stubbs and I agreed the expression was a reasonable basis to explain and explore the interaction of present-day impacts of extreme events and the potential impacts of climate change on Australian environments and society. I have found it very helpful in providing a more real world context for decision-making by explaining risk as a function of both historic and climate-change related factors.

Recently, historic and climate change related coastal vulnerabilities have been incorporated into objects of the NSW Coastal Management Act 2016. Object (f) in this Act specifies that it is necessary “to mitigate current and future risks from coastal hazards, taking into account the effects of climate change”. And to further support this point, object (i) states “to encourage and promote plans and strategies to improve the resilience of coastal assets to the impacts of an uncertain climate future including impacts of extreme storm events”.

Clearly coastal managers need to think of coastal vulnerability in both its historic and future contexts in determining risks. What then is the risk appetite of communities to use both components of vulnerability in their land use plans and management practices? In NSW consideration of risk appetite in land use planning and management of built and natural assets will be a matter of deliberation in the development of new Coastal Management Programs.

Words by Prof Bruce Thom. Please respect Bruce Thom’s thoughts and reference where appropriately: (c) ACS, 2016, posted 8th December 2016, for correspondence about this blog post please email