Wednesday, April 20, 2016

This is how far seas could rise thanks to climate change

Picture yourself on a beautiful beach, anywhere in the world. Your favourite beach, maybe. The waves are lapping on the shore, the Sun is sparkling over the water and there is a refreshing ocean breeze.

Now imagine this beach has gone forever. Sea level has risen and the shoreline has moved inland by hundreds of metres, drowning stretch after stretch of former coastline in the process.

It might be a struggle to envision dramatic transformations to such familiar places, but climate change scientists say there is overwhelming evidence that sea levels are indeed rising, and at a rapid rate. So how high will sea levels go? And at what cost to coastal communities?

It was in the early 20th Century that scientists first realised that sea levels were on the move.

In 1941 Beno Gutenberg, a geophysicist, analysed the data from tide gauges – instruments along coastlines that measure sea level – and noticed something odd. Over the period that reliable tide gauge data existed at the time – about 100 years – sea level was rising.

The melting of the world’s glaciers and ice sheets could release vast quantities of water into the oceans 

Tide gauge data is now considered quite unreliable, but in 1993 NASA and the French space agency sent satellite-borne radar altimeters into space. Consequently we now have a much more accurate picture of sea level over the entire globe. These instruments confirmed that sea level is rising.

We now know that our warmer climate is driving the change. For instance, simple physics tells us that as water warms up, it expands.

“Thermal expansion through warmer ocean waters was the largest contributor to global sea level rise over the past century,” says John Krasting, a physical scientist at the US National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory.

This thermal expansion will continue, but there is another, more notorious problem that could lead to really dramatic changes in sea level in the future: the melting of the world’s glaciers and ice sheets could release vast quantities of water into the oceans. How bad could it get? More