How do we know how fast sea levels are rising?

Rising sea levels is one of the most worrying consequences of global warming, threatening over 100 million people living in vulnerable coastal areas. But measuring the rate of the rise is fraught with difficulty.

3rd December 2015
How do we know how fast sea levels are rising?

Asked by: Will Robinson, Southampton

Rising sea levels is one of the most worrying consequences of global warming, threatening over 100 million people living in vulnerable coastal areas. But measuring the rate of the rise is fraught with difficulty. For over 150 years scientists relied on so-called tide gauges, which monitored the rise and fall of floats in tubes. However, such gauges proved vulnerable to errors – not least the rise and fall of the land. Satellite measurements based on radar are now used but these too suffer from subtle errors caused by orbital, instrumental and atmospheric variability.

The need for precision is vital as the expected change in global sea levels is no more than a few millimetres a year. Earlier this year, the journal Nature Climate Change published the latest attempt to iron out the problems and the report suggests the Earth’s oceans are rising by around 2.8mm per year. While this might not sound much, it’s enough to prove a serious threat over the next 100 years.

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