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Why is the baseline period for the sea level rise projections different from the UKCP09 1961-1990 baseline?

The sea level rise estimates are based on IPCC Fourth Assessment Report results, it is therefore appropriate to use the same present day baseline of 1980–1999 for absolute sea level rise for consistency purposes.

In detail

Much of the UKCP analysis uses a baseline for present-day of 1961–1990, for consistency with earlier and UKCIP02 scenarios. Because the time-mean sea level rise estimates are based on IPCC Fourth Assessment Report results, it is appropriate to use a present day baseline of 1980–1999 for absolute sea level rise for consistency. This difference in baseline will not greatly affect the results.

Users wishing to translate the absolute sea level rise results to the 1961–1990 baseline period are recommended to add a further 2.5 cm of sea level rise to the future projection. This is based on there having been an observed global rate of sea level rise of approximately 1.8 mm/yr for the period 1961–2003 (IPCC 2007, Chapter 5). To correct the relative sea level rise, take the appropriate vertical land movement from Figure 3.5 of the Marine & coastal projections report (see Find out more, below) and multiply this by 15/10 (15 yr from 1975 to 1990, 10 mm/yr = 1 cm/yr). This value should be subtracted from the corrected absolute sea level values to give the local relative sea level rise in 2095 with respect to the 1961–1990 period.

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