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Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Dr Megan Saunders is a postdoctoral researcher at the ARC Centre of Excellence for Environmental Decisions and The Global Change Institute, The University of Queensland
Hansen and colleagues conducted a novel study to understand the amount of sea-level rise that we might expect in the next 50-200 years. They used three lines of evidence to understand how CO2 emissions from human activities affect sea-level rise: 1) computer models - which are kind of like weather forecasts, 2) studies of past sea-level, and 3) studies of present climate and sea-level rise.
They used these different approaches because each one has strengths and weaknesses, but taken together the total information is greater than the sum of its parts. They found that sea-level rise over the next 50-200 years could be several metres or more.
This is significantly greater than the amount - up to around one metre - estimated in the most recent Intergovernmental Panel on Climate Change (IPCC) report.
Sea-level rise of this amount will have extremely serious consequences for coastal societies. 85 per cent of Australians live within 50 km of a coast, and over 1.3 billion currently live within 100 km of a tropical coastline.
Rapid sea-level rise will affect infrastructure, communities and ecosystems on coasts, which will have serious economic consequences for coastal societies. Early planning for sea-level rise is essential to minimise the costs and damage. Rapid sea-level rise will cause flooding, shoreline erosion, and loss of coastal habitats like mangroves, saltmarshes, seagrass and coral reefs, which people rely on for fisheries, building materials, clean water and protection from storms.
This study highlights that action to minimise CO2 emissions is urgently required to keep temperatures below +2°C warming, which will reduce the risk of rapid sea-level rise.
Dr Duanne White is an Assistant Professor at the Institute for Applied Ecology, University of Canberra
Information from past climates indicates that small changes in temperature (e.g. 1°C), given enough time, can produce several to tens of metres of sea level rise. However, in many ways, the speed of future changes will be the main control on the ability of people, economies and the environment to adapt to sea level rise. Projections from the IPCC provide a good minimum estimate of future rate of change. However, there are substantial, but poorly quantified risks on the high side, which may mean that the IPCC estimates are an order of magnitude too low and thus impacts on communities are underestimated. This paper provides an example of one of those risks, thoroughly documenting one potential, previously unconsidered, feedback mechanism around ice-ocean-atmosphere interactions that would mean we are currently underestimating the likely magnitude and affects of future sea level rise.
John Church is an Emeritus Professor in the Climate Change Research Centre, University of New South Wales.
My thoughts on this paper are in the IPCC chapter and also The Clark et al. update to this. Briefly, in these reports we expressed concern about large multi-metre sea level rise and long term commitments (consistent with the Hansen paper), but that the rise by 2100 is likely less than one metre (inconsistent with the Hansen assumptions). These multi-metre sea level rise commitments could well occur this century, particularly with the higher emission scenarios. Even with the lower emission scenarios we have committed the world to ongoing sea level rise for centuries.