A couple of years ago I posted* in response to a post on sea level rise at The Conversation
A senior geology professor in Miami, who also chairs the science committee for the Miami-Dade Climate Change Advisory Task Force, has views on future sea level rise that are way more extreme than the available evidence.
My Summary started
The claim by Professor Wanless at the Conversation that sea levels could rise by 1.25 to 2m by 2100 is way too extreme it is based on top-slicing the estimates on a NOAA 2012 report. The top-end estimates were not included by the UNIPCC in its AR5 Sept 2013 report. In fact, the UNIPCC report stated it had low-confidence in estimates of sea level rise above its top-end 0.82m.
The Task Force has now concluded. The Miami-Dade Climate Change website states
The Sea Level Rise Task Force, formed in July 2013, developed several important recommendations, which are being implemented in Miami-Dade County. The Task Force reviewed relevant data and prior studies and reports regarding the potential impact of sea level rise on public services and facilities, real estate, water and other ecological resources, and property and infrastructure.
The Introduction to the extensive report report states (with conversions into mm inserted):-
Since reliable record keeping began over 100 years ago at the tide gauge in Key West, the average sea level has risen approximately 228 millimeters (or 9 inches). This rise has been primarily due to thermal expansion (as warmer water occupies more volume) and to melting from glaciers and ice sheets. Over the next century, the rate of sea level rise is very likely to accelerate due to increased melting from land-based ice sheets, in particular Greenland. Recognizing the need for clear, consistent, and local information about future sea level rise projections, The Southeast Florida Regional Climate Change Compact developed the, “Unified Sea Level Rise Projection for Southeast Florida”. The updated projection, published in 2015, was developed by a panel of well-respected and informed scientists using the most recent and best available data. The projection (Figure 1) estimates that the region can expect to see average sea levels 6 to 10 inches (150 to 205 mm) higher by 2030 than they were in 1992, 14 to 34 inches (355 to 860 mm) higher by 2060, and 31 to 81 inches higher (790 to 2060 mm) by 2100. There is a more certain estimate for near-term changes and a greater uncertainty for estimates at the end of this century. This change in average sea levels will amplify the risks of storm surge and nuisance flooding.
This implies a massive acceleration in the rate of sea level-rise. In the last couple of years the rate of sea level rise has indeed accelerated. The NOAA data now shows a rate of 237 mm a century, by from 228 mm when the report was written. It is likely a blip and well with the margin of error.
To see how much sea level rise will have to accelerate to meet the forecasts, I will assume that from 1992 to 2015 the sea levels rose by 60 mm (2.4 inches) or 2.6 mm a year.
From 2016 to 2030 sea levels will need to rise by 6 to 10 mm a year on average, or about three or four times the current rate.
From 2016 to 2060 sea levels will need to rise by 8.5 to 23 mm a year on average, or about three or nine times the current rate.
From 2016 to 2100 sea levels will need to rise by 8.5 to 23.5 mm a year on average, or about three or nine times the current rate.
The impact of Professor Wanless on the Committee’s output should be clearly seen. A straight line forecast would be a 8 to 9 inch sea level rise by 2100. Many of the recommendations for planning will be based on a 2 foot 6 inch rise to a 6 foot 6 inch rise. Any reasonable person should take a measure to the Miami-Dade area – which is very low-lying and imagine the difference between a dyke 12 inches high and a dyke seven feet high along the Miami sea front.
Alternatively imagine the effect on property prices in Miami-Dade (2.6 million) and on neighbouring Broward and Palm Beach (3.1 million) if people really swallowed this whole. The tiny community of Fairbourne (724 people) in West Wales have had their properties made virtually value-less by a Welsh Government report and the alarmist reporting by the BBC.