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Extreme weather, climate change, and people: academic views

Floods hit Maitland, NSW, in 1955. Flickr/Cultural Collections, University of Newcastle.

The Intergovernmental Panel on Climate Change (IPCC) will tonight release from its meeting in Kampala, Uganda, a summary for policy makers of a forthcoming report titled Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation.

In a 2009 scoping paper for the report, the IPCC gave the background to its inquiry:


Ahead of tonight’s release of the summary report, a range of academics here discuss aspects of the relationship between extreme weather, climate change, and humans - what they do and where they live.

Dr Natasha Kuruppu, Senior Research Consultant, Institute for Sustainable Futures, University of Technology, Sydney

There is a large body of literature on natural hazards that have repeatedly demonstrated that it is the social-economic, political and cultural processes that shape how people cope and respond to extreme weather events such as what we witnessed during the floods in New Orleans. This vulnerability is constructed socially; its underlying causal factors are predominantly social, rather than biophysical and are rooted in the socio-political process that allocate resources in a society. We may be hit by frequent extreme events as a result of anthropogenic climate change or natural variability but the focus should not only be on mitigation alone.

There is a huge need to simultaneously address deeper issues that give rise to social vulnerability i.e., unequal access to resources, political, cultural and social inequalities that shape the extent to which people and communities are impacted and their ability to respond to those impacts. This is being done to some extent through climate adaption planning both at the international and country level but there is a huge deficit in funding for such initiatives. This is particularly pertinent when we think about the social justice issues around climate change in which many of the countries and communities that will be affected most by extreme events are those living in developing countries or indigenous communities on the margins who have contributed least to global emissions are have to deal with issues of double exposure i.e., the interactions of climate change and other processes of globalisations such as increased urbanisation, poverty etc. Irrespective of how climate change impacts are projected, the issue also needs to reframed from a social justice or human rights angle in which increased extreme weather events or climate change in general will threaten the rights of many citizens to secure a life that they value.

Some of the dead of a 2009 landslide in the Philippines that killed about 200 people. The landslide was triggered by Typhoon Pepeng (known outside the Philippines as Parma). Flickr/Mr. Daniel Ted Feliciano

Professor Christian Jakob, ARC Centre of Excellence for Climate System Science, Monash University

We all experience climate as a sequence of weather events. Climate can in fact be understood as the collection - or in technical terms the probability density function - of weather. Consequently, we will experience climate change as a change it the weather. This includes both the “mean” weather and extreme weather events. Extreme weather events are by their very nature rare - they populate the far ends of the distribution of weather. As a consequence detecting changes in extreme events due to climate change is significantly more difficult than detecting changes in the mean climate and requires more comprehensive and longer data records. This results in somewhat larger uncertainties in identifying the link between climate change and changes in extreme events in observations. This does not imply that the climate is not changing, nor does it imply that changes in extreme events won’t be part of that change. The larger uncertainties in observing the current state and projecting the future of extreme weather events around the globe highlight the need for continued research into the link between climate and extreme weather.

The Buckingham Bridge in Kelmscott, WA, buckled when a bushfire swept through in February, destroying about 70 homes and killing an unknown number of animals. AAP/Tony McDonough

Associate Professor Stewart Franks, School of Engineering, University of Newcastle

Australia has a long and detalied history of climate variability - however, we now have a new threat - anthropogenic climate change caused by human CO2 emissions. Despite the long history of climate extremes there is a clear danger that we might now interpret every flood or drought as CO2 climate change. As a scientist who studies extreme hydrological events, I can only report that there is no evidence of “change” in terms of their occurence. The sad reality is that catastrophe is a natural phenomenon. The droughts of the early 20th century, and the widespread floods of the 1950-1970s is testament to the reality - extreme events do happen, but it is not always our fault. To date there is no published study that proves otherwise, though the claim is too often made by those that ignore the past.

Security forces take few risks as they evacuate New Orleans residents in 2005 after Hurricane Katrina caused levees to fail and much of the city was flooded. AAP/EPA/Larry W. Smith

Dr Stuart Corney, Climate Systems Modeller, University of Tasmania

It is difficult to distinguish between the change in frequency of low-probability events (extreme events) and the likelihood that such events will become more common in the future. Extreme events have always occurred due to natural variability in the weather, however current scientific evidence (as supported by the IPCC) suggests that the frequency of these low probability events is changing, and that they will become more common. Some studies have already provided evidence that recent extreme events can be partly attributed to anthropogenic climate change, for example a study published in 2010 in Nature which attributes the change in probability of flood risk in England and Wales to climate change. I believe the not-yet-released IPCC Special Report on Extreme Weather will discuss the complexities in the process of detection and attribution of such low probability events to anthropogenic climate change.

There is much evidence that the climate change signal will continue to emerge and certain extreme events will become more likely in the future. As an example, on the east coast of Tasmania a 1-in-50-year rainfall event (for the current climate) sees approximately 125 mm of rain falling in a 24 hour period, while a 1-in-1000-year rainfall event sees approximately 175 mm of rainfall on a single day. Current research, recently released by the Climate Futures for Tasmania project states that by the end of the century a 1-in-50-year rainfall event will see 175 mm of rainfall in a single day. Many studies, including the soon to be released IPCC Special Report on Extreme Weather, suggest that extreme events, such as extreme rainfall, fire weather or heat waves, are likely to become more common

The difficulty arises though when we try and link a single event to climate change (this process is known as detection and attribution). Going back to the East-Coast of Tasmania example, if 175 mm of rain falls on a single day is this a 1-in-1000 year event in the current climate, or is this event expected to happen more often due to a changing climate. It is only when a number of these events happen that statisticians can start to distinguish between the very unlikely 1-in-1000-year events and the more likely (but still uncommon) 1-in-50-year events.

To summarise, any single weather event, no mater how unlikely or extreme, has a chance of occurring in the current climate, and thus cannot be indisputably attributed to climate change (even events that in the current climate are only expected to occur once every 10 000 years can still occur today, but are very unlikely to occur twice in the next century). It is only through the careful study of the pattern of events over years or decades that we can begin to attribute the changing pattern of our weather to climate change. The soon to be released IPCC Special Report on Extreme Weather states that extreme events are likely to become more common, however at this stage it is still difficult to confidently say that we have already seen a change in the frequency of such low-probability extreme events. If we do not change our emissions behaviour then it will become easier over time to show that extreme events are happening more often, but this is probably not a path we want to go down.

On the edge of a camp in Dadaab, north-eastern Kenya, a young girl stands amid the freshly made graves of 70 children, many of whom died of malnutrition in this year’s famine. Flickr/Oxfam East Africa

Peter Macreadie, Chancellor’s Post Doctoral Research Fellow, University of Technology, Sydney

What people forget is that spreading human settlement has indirect effects on weather through release of greenhouse gases. When the Sacramento Delta marshes was drained to make way for more houses, it led to massive release of CO2. Around 1 gigatonne of CO2 was released from a single marshland – that’s equivalent to 1.5 per cent of California’s total greenhouse gas emissions, or the cutting down of half the trees in California. That CO2 took around 5000 years to accumulate, yet it was released out into the atmosphere in just 100 years. This sort of thing is also happening in Australia. For example, in a recent study (Global Change Biology, in press) we found that humans have dramatically weakened the ability to capture and store carbon. Using paleoreconstruction, we went back in time – more than 6000 years – and monitored carbon capture and storage by coastal ecosystems. We found that there was been around a 100-fold weakening in the ability of coastal ecosystems to sequester carbon since the time of European settlement. In other words, we have severely hampered the ability of nature to help reset the planet’s thermostat.

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