The Met Office’s Sea Level Trick

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By Paul Homewood

Sea levels have risen by around 16.5cm (6.5 ins) since 1900, but the Met Office says the rate of rise is increasing. They are now rising by 3-5.2mm a year, which is more than double the rate of increase in the early part of last century.

UK Sea Level Rise Speeding Up–Claim Met Office: Data Proves Otherwise

You will recall this BBC report last week, which I debunked here.

One of our readers asked the Met Office for evidence of their claim. They wrote back:

We have heard back from our relevant team. Please see below:
There is a clear acceleration in reconstructions of global mean sea level change based on global tide gauges since about 1960, as can be seen in Figure 1 of this paper:
https://iopscience.iop.org/article/10.1088/1748-9326/abdaec
The following statements, which represent the scientific consensus on climate change, come from the IPCC Sixth Assessment Report of Working Group I, Summary for Policy Makers [IPCC AR6 WG1 SPM, available from: https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf]:
“Global mean sea level increased by 0.20 [0.15 to 0.25] m between 1901 and 2018. The average rate of sea level rise was 1.3 [0.6 to 2.1] mm yr–1 between 1901 and 1971, increasing to 1.9 [0.8 to 2.9] mm yr–1 between 1971 and 2006, and further increasing to 3.7 [3.2 to 4.2] mm yr–1 between 2006 and 2018 (high confidence). Human influence was very likely the main driver of these increases since at least 1971.”
The acceleration in global mean sea level rise is in part related to the observed increase in ice sheet mass loss in the recent two decades: “The rate of ice-sheet loss increased by a factor
of four between 1992–1999 and 2010–2019. Together, ice-sheet and glacier mass loss were the dominant contributors to global mean sea level rise during 2006–2018 (high confidence)” [quote also from IPCC AR6 WG1 SPM].
At local scales, there are a number of additional factors than can shape the rates of sea-level rise, including internal variability at decadal timescales. This means that it can take longer for accelerations to manifest in individual tide gauge records.

Note that they are comparing the period since 1971, with the period 1901 to 1971. This, however, is the worst sort of cherry picking, because the 1970s were in the middle of a slow down in sea level rise, caused by global cooling in the 1960s and 70s. Some researchers also point to the era of global dam projects at the time being responsible for impounding water, thus lowering sea levels.

This slowdown is readily apparent on the chart below, which the Met Office has linked to:

https://iopscience.iop.org/article/10.1088/1748-9326/abdaec

It is also clear that the rate of sea level rise between 1920 and 1960 was similar to recent decades.

The effect of that slow down in the middle, of course, is to depress the average rise between 1901 and 1971, while at the same time increasing the trend since 1971.

The Met Office was, you may recall, talking about UK sea level rise, and we can see the very same pattern here. At North Shields, for example, the rate of rise peaked between 1920 and 1970, then fell to its lowest for 1945 to 1995:

And we can see similar trends at other tide gauges around the world:

What the Met Office have essentially done is to measure the rise over the upward part of the cycle, and compare it with the full part of the previous cycle. Look again at that graph: