London Thames Barrier update

Update: here is the transcript of Hansen's latest "in plain English" (here if PDF download fails)

Two weeks ago I recreated Sea Level Rise (SLR) and Risk of Flooding (RoF) maps for the lower Thames River near the Thames Barrier (blog) for a WhatsApp Group considering the future of its ageing infrastructure w.r.t. recent climate extremes. This week came a global and urgent update affecting Sea Level Rise, by James Hansen who sounded the alarm ~ 35 yrs ago (go to 1981 & 1988 in Medium): a paper incl. supplementary materials "Global Warming Has Accelerated" (Columbia) c/w companion webinar (Columbia).

I mapped conservatively up to 6 m. SLR in my previous blog. But as Extinction Rebellion Scientist in Cambridge UK, I mapped up to 12 m. SLR from increased polar ice melt before the Pandemic. The recent discussion by Hansen above led not only to further upgrade that to 15 m. SLR, but also to shorten IPCC anticipated end-century timeframe to mid-century!

PDF here

Here is the original SLR & RoF map blogged recently based on Ordnance Survey (OS) topography; as a reminder, SLR is a simple model intersecting incremental elevations against topography:

click to enlarge (full A0 plot here)

Here is the updated SLR & RoF map with two key differences:

• the topography used here is Climate Central's on a no-cost non-commercial license (75 m. resolution slightly down from 50 m. OS): it removes infrastructure and vegetation for better ground-truthing - see the consequence here at a global level of those new calculations published in 2019
• the timeframe is moved up from 2100 to 2050 due to the combined factors discussed above

click to enlarge (full A0 plot here)

If risk of inundation looks more severe here, it's because it is... for two reasons:

• SLR is modelled via incremental elevations against topography: the latter, lowered by an avg. 2m. globally, vastly increases the affected areas as discussed by Climate Central above
• SLR increment is raised to 15 m.: warmer El Niño, accelerated polar ice-melt, lesser cloud albedo and potential AMOC reversal discussed in the opening paper / video caused this upward revision

Here is what the difference looks like, using the same map plotting trick for SLR as for RoF:

• the original RoF opaque blues are now the original SLR opaque rainbow colors
• the original up-to-6 m. SLR halftones atop are now the up-to-15 m. SLR halftones to show the wider affected areas

click to enlarge

The stark contrast between the original mustard color overlays against the new rainbow color extents, shows the significant range increase due to this update. Even without running statistics, it underscores Climate Central's estimates of increased areal impact. 

An update will be run on CoastalDEM v.3 licensed this year, against v.2.1 used in 2020 and currently shown. All sources and attribution appear on A0 maps linked above.

To recap, what was a "far-tail" scenario at 12 m. SLR ca. 2150, is now drastically brought forward to 2050, due to newly studied and combined accelerated climate effects. In addition, the targeted 1.5°C annual increase has already been reached and replaced by possible 4°C annual increase that is not sustainable.