Now, what I want is Facts

The climate change discourse is awash with facts but since 2007 there has been scientific consensus around an important one that ‘most of the warming observed over the last 50 years is attributable to human activities’.  This was the statement issued by the authoritative Intergovernmental Panel on Climate Change (IPCC) in 2001 from which no national scientific body of national or international standing now maintains a dissenting position.

Here we look at some important figures and answer one of the questions we are asked repeatedly – how far have sea levels risen already?

The IPCC (2007) states that there was ‘little change’ in sea levels from 0 AD to 1900.  However, since the end of the Little Ice Age in the mid-nineteenth century sea levels have been rising at an accelerating rate.  A 2cm rise in the eighteenth century became 6cm in the nineteenth and 19cm in the twentieth.  Since the early nineties satellite technology has been used in addition to the measurements of tide gauges creating even greater confidence in our observations.  This data shows that in the 1990s the rate of sea level rise was equivalent to 30cm in a century and that today we are nearer to a 40cm rise.

Historic Sea Level Rise

This graph (IPCC, 2007) presents global mean sea level as a deviation from the average sea level for the years 1961 to 1990.  The red dots show reconstructed sea level fields since 1870; the blue curve shows coastal tide gauge measurements since 1950 and the black curve is based on satellite readings.  Error bars show 90% confidence intervals.

The figures presented here are of course global averages which mask important regional variations that indicate which parts of the globe will be worst hit.  We will turn to this in the next installment and answer questions such as why is sea level at the Caribbean end of the Panama Canal 20cm higher than at the Pacific end?  How is it that the sea level around Antartica appears to be going down but is in fact going up?  And what is it that’s so special about Weston-super-Mare?

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