Sea level rise creeps up… very slowly… at first
As with many people climate change science has been on my mind with the devastation of the floods and now hurricane Yasi in Queensland.
Sea level rise is one of the likely impacts of climate change, driven by a melting of the Greenland Ice cap. The melting of the Greenland Ice cap will lead to a sea level rise of around 7 metres. I was a bit sceptical about this number when I learnt of it. How could the ice melt from such a seemingly insignificant place on the world (after all, who do you know who has been to Greenland?) cause such a high sea level rise? So I did some quick investigation, found out that most of the Greenland ice shelf was over one km thick, and a rough calc showed that this estimate of sea level rise was about right. But how long would this take? Surely it would be over hundreds or thousands of years?
If you have ever seen a presentation by David Suzuki or can remember your high school science, or understand compound interest, you should appreciate the concept of exponential growth. For example, which would you prefer – $1 million or 1 cent that doubles every day for the next thirty days? If you opted for the 1 cent that doubles after 20 days you’d only have a little over $5,000, but after 30 days you would have over $5 million. With exponential growth nothing much seems to be happening, then suddenly things seem to change very quickly.
The Climate Code Red blog has recently reported on research by NASA scientist James Hansen that indicates that the rate of mass loss from the Greenland ice shelf is doubling roughly every 5 to 6 years. Hansen is quick to point out that the data records are too short to be sure of the doubling time. But if the rate of mass loss does double every 6 years, after 60 years the rate of mass loss will be over 500 times what it is today. And this exponential growth in the rate of loss of ice is what Hansen has predicted could translate into a 5 metre sea level rise by 2095.
Over the last century the sea level rose by somewhere between 150 to 200mm (according to the USA’s environment protection authority). Lets assume that that the sea level rose by say 2mm in 2010, in line with the average yearly rise in the century before. If we take the crude approximation that sea level rise also takes place exponentially, and we are looking at a sea level rise of 5 metres by 2095, by how much will the sea have risen between 2010 and 2020? By just 30mm – surely nothing to make the alarm bells ring or make coastal property values plummet. By 2030 the rise will be 80mm – mmm. By 2050 the rise would be 330mm. Probably still not enough for some sceptics to acknowledge climate change. In fact it would only be until 2068 that sea levels were a metre above 2010 levels.
Now I’m not a climate change scientist and the numbers above have been generated from some very rough calculations that wouldn’t stand up to peer review. But my point is that sea level rise – seen as one of the great threats of climate change – will probably creep up on us. Just because its happening slowly now doesn’t mean sea level rise will always be slow.