The effect of wind driven waves as a result of climate change could make Australia lose more of its coastland than previously thought, according to a new research by a University of Newcastle palaeoclimatologist.
As part of his study, Dr Ian Goodwin looked at how the changing direction and height of waves might affect coastal erosion. The findings, which were presented at the recent Greenhouse 2007 conference in Sydney, showed that in one scenario, storm surges had the possibility of eroding beaches on Australia's east coast by as much as 100 metres over the next 100 years.
Dr Goodwin said this was in addition to land loss due to climate-change related sea level rises. Current Australian models of how the coast will disappear rely only on sea level rises and don't take into account the effect of 'wave climate'.
Dr Goodwin said, "the impact of these wave climate changes was about half of the impact of sea level again". During the course of his research, Dr Goodwin, along with Dr Peter Cowell from the University of Sydney, also examined the evidence of ancient coastlines buried in coastal dunes along Australia's east coast.
With the help of CSIRO, they collected and dated sediment samples as far back as 3500 years taken from sites between Fraser Island in Queensland down to Newcastle in New South Wales.
The duo then determined when these sand grains were deposited. The researchers found a regular change in the shape and orientation of beaches and the amount of coastal retreat that correlated with changes in the Southern Oscillation Index.
Under El Niņo drought conditions, waves tend to come from the south, bringing more sand onshore, fleshing out the beaches. But under rainy La Niņa conditions, they found, less sand was brought onshore and storm surges ate up the beaches.
According to Dr Goodwin and Dr Cowell, the problem is that scientists don't agree whether La Niņa or El Niņo conditions will dominate in the future. So, it is difficult to predict which pattern of wind and sand will affect the coast, said Dr Goodwin, adding that the team has found that wave direction could change by 20 degrees.
"That presents a huge uncertainty in the magnitude of the potential change to the coastline. On the negative side, wave climate might be responsible for subtracting 100 metres of coastline over 100 years," he said. "Add that to the 120-130 metres lost due to a 0.5 metre sea level rise, and it can make a big difference to safe coastal developments," he added.
Dr Goodwin said current developments tended to favour the relatively protected southern end of beaches further up the coast. "But, it is the ends of the beaches that are most at risk when it comes to wave climate, and the effect of wave climate also gets worse the further north he studied. This in creases our vulnerability to climate change," ABC online quoted him as saying.