Matthew Lambourne, Mullumbimby
Jim Mangleson seems to be a bit confused about rising sea levels (Letters, 35.27). He is quite right to say the sea level in Sydney has risen around 65mm over the last 100 years, but that is only one place around Australia’s thousands of kilometres of coastline.
Taking other gauges into account, the rise is around 200mm, not far from the global average of about 250mm. Jim goes on to say ‘the water was much warmer and the sea level much higher’ 6,000 years ago.
Quite right, and nothing to do with ‘diesel cars’, but it was the ending of the last ice age. Since then, temperatures and sea levels have been slowly dropping as we headed towards the next ice age, until around 150 years ago when land clearing, agriculture and fossil fuel burning changed things around.
Temperatures, after dropping maybe 2°C over 6,000 years, have risen more than 1°C in 150 years. If Jim’s 3 metre drop in sea level is right, that is 0.5mm per year over those 6,000 years – now sea level is rising at about 4.5mm per year, including in Sydney.
That is the problem – a natural slow drop in temperatures and sea level has been changed, by us, in 150 years to rapidly rising temperatures and sea level.
These rates of rise are accelerating, particularly sea level which lags behind temperature as higher temperatures penetrate into the deep ocean.
We don’t need computer models to see where this is going, a simple sea level/temperature correlation including an appropriate time lag shows we are heading for the same sort of future sea level rises as the computer models suggest.
We have been warned.