Skip to navigation | Skip to content


Hedging bets against sea level rise

Cairns flooding

Sea level rise leads to more frequent coastal flooding, say experts (Source: Cairns Regional Council)

Rising seas While science is zeroing in on the relationship between global warming and sea level rise, planning for coastal flooding is still a bit of gamble, according to new research.

A new report, by the Antarctic Climate and Ecosystems Cooperative Research Centre, summarises the latest data on sea level rise.

"The science is advancing all the time," says report co-author, oceanographer Dr John Hunter. "That's why we've produced an update."

Hunter says sea levels are currently rising at 3 millimetres per year and the most recent research has found that about half of this is due to expansion of the warming ocean, and about half is due to melting of ice.

"Being able to identify the individual components of what's going on at the moment is a big advance in enabling us to improve our models of sea level rise," he says.

"Now we really can explain why sea levels are rising."

Hunter says according to the best available evidence if nothing is done to curb greenhouse emissions, global average sea levels will rise by about half a metre over the next century.


Research shows that different parts of the globe will experience different degrees of sea level rise.

For example, while most of Australia is expected to get sea level rises close to the global average, he says the eastern states will have a slightly higher rise.

Research by the Centre and the CSIRO suggests that the east coast could experience a sea level rise of about 10 centimetres greater than the global average over the coming century.

Hunter emphasises humans will not experience a gradual increase in sea level but instead see an increase in the frequency of coastal flooding.

As a rule of thumb, he says, for every half-metre increase in sea level, there is a 300 times increase in frequency of coastal floods.

So, for example, a flood that normally occurs once every 100 years would occur instead several times a year.


Hunter says while the scientific models are "not bad", there is still huge uncertainty in them and actual sea levels could rise by as little as 0.2 metres to as high as 0.8 metres, or even more, over the next century.

He says this range exists because of scientific uncertainty over how fast the polar ice sheets will melt, as well as uncertainty over how greenhouse emissions will change.

To complicate matters there is a big lag between any change in emissions and change in sea level.

"If we change our emissions today, you won't see it in the rate of sea level change for many decades," says Hunter.

Hedging bets

But, Hunter says, all this uncertainty doesn't mean we can't plan for sea level rise.

By combining information on sea-level rise with that on present storm surges and tides, scientists can estimate a statistical likelihood of future flooding events to help with risk assessment.

"What you get at the end of the day is the number that a gambler would use," says Hunter.

"It's the same order of uncertainty as we have to deal with in our daily life," he says, likening the uncertainty around climate change to that around life expectancy.

"We gamble with life expectancy all the time," he says. "We don't know when we're going to die so we take out insurance."

"We have a big uncertainty around sea level rise but we have just got to learn to deal with it in a rational way like we would deal with any other risks that aren't uncertain."

Tags: floods, climate-change, erosion, oceans-and-reefs, research