AR6 Sea Level Rise

WG1 Technical summary (Box 4.2)  states:

“Global mean sea level (GMSL) increased by 0.20 [0.15 to 0.25] m over the period 1901 to 2018 with a rate of rise that has accelerated since the 1960s to 3.7 [3.2 to 4.2] mm yr-1 25 for the period 2006–2018 (high 26 confidence). Human activity was very likely the main driver of observed GMSL rise since 1970, and new 27 observational evidence leads to an assessed sea level rise over the period 1901 to 2018 that is consistent with 28 the sum of individual components contributing to sea level rise, including expansion due to ocean warming 29 and melting of glaciers and ice sheets (high confidence)”

However if you look at the actual measurement data made by tidal gauges and satellite altimetry , then you find something quite different .

Tide Gauges and satellite data (Topex/Possieden)

You can see 3 distinct trends. Before 1925 a long term trend of increasing sea levels of 1.3mm/year is seen and from 1925 until 1993 the trend is 1.8mm/year. This appears to be  a systematic shift rather than any physical “acceleration” effect,  perhaps due to a more consistent set of gauges after 1925. There is no evidence of an accelerating trend up until 2000. Thereafter the satellite data from Topex/Jason-123 shows a small systematic step increase in trend to ~2.8mm/year. This increase from 1.8 to 2.8mm/year is interpreted as an “accelerating” sea level rise, but it looks suspiciously like yet another instrumental effect. Indeed there is no acceleration visible within the satellite series data itself.

This satellite data with seasonal effects removed shows a stable trend of ~3.3 mm/year. At this rate we would expect a sea level rise by 2100 of  only a further 26 cm. Yet AR6 is implying far larger rises. In fact the rises they project seem much larger because they all  assume  an accelerating rise.

Likely range between 1 and 1.7m rise in sea levels by 2150 assuming accelerating rise.

If instead we extrapolate the satellite data forward to 2150assuming a continuous linear rising trend of 3.3mm/yr than we get a net rise in sea level of 60cm since 1945. This  corresponds to just a 45cm rise on the AR6 baseline (zeroed at 2100)

Baseline is zero in 1950

Sea level rise is probably the most alarming climate change prediction because many major cities are located on coasts or estuaries with protected harbours. Sea levels have been rising continuously since  the last glacial maximum (100m lower than today). There is no firm evidence that convinces me this rise has accelerated significantly in recent decades. So if we assume that the satellite data are the most accurate measure of trends then we can expect a 45cm rise by 2150 relative to todays levels. The daily tidal range in London reaches as much as 7 meters, so the London barrage should easily be able to cope with an extra 45cm in 150 years time. If not we will have plenty of time to upgrade it.

 

Posted in AGW, Climate Change, SLR | 15 Comments

Global Temperature for June remains unchanged at 0.69C

After the first 6 months 2021 looks set to be the coldest year since 2014. The annual global average temperature calculated so far is 0.64C relative to a baseline 1961-1990. The June monthly temperature has remained unchanged since May (0.69C), although there are differences in the spatial distributions.

Annual global temperatures (2021 – first 6 months)

The monthly temperatures show an insignificant change relative to the May value keeping the annual average essentially the same as well.

Monthly temperatures. May and June 2021 are essentially the same.

There are however changes in the spatial heat distribution since May, but a strong La Nina effect remains in place. Here is an animation of the 3D temperature distribution in June. The southern hemisphere remains much cooler than normal. There is also evidence of a ring of warmer temperatures encircling the earth  at ~40N.

The southern hemisphere remains “cooler” .

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Global Temperatures – May 2021

The Global average temperature for May was 0.69C an insignificant rise of 0.05C since April.

Monthly temperature anomalies relative to a 1961-1990 baseline. See this post for details

After the first 5 months 2021 is already significantly cooler than 2020. Here is the annual average up to May.

Annual Global Temperature Anomaly (first 5 months of 2021)

Europe and Eastern US were colder than normal

As was the Southern Hemisphere

May temperatures in the Southern Hemisphere.

There is also  a strong La Nina effect  in 2021

Strong La Nina ?

At least we have had a few warm days in the UK to cheer us up a bit and take our minds off the Global Pandemic “Emergency” and loss of most civil liberties !

Posted in AGW, Climate Change | Tagged | 13 Comments