A tale of three models

Sea level rise models show that climate change science is hard

Andrew Zolnai
Nov 5 · 4 min read
East Anglia coastal inundation models +5m sea level rise: CReSIS 2005, Firetree 2006 & ClimateCentral 2019

A tale of two maps contrasted CO2 emission by country and over time, in simple yet visually compelling bubble animations. Tech posts on my pro channel detail the means to do so: here we’ll post open data web maps, and the contrast will be in the modelling used to derive three maps.


I have blogged on East Anglian geo-history for almost a decade, initially to provide open source maps based on open data for the now defunct Fenlands Heritage Environment Project.

East Anglia is a contrast of of a flat expanse at or near sea level south of the Wash, and uplands of low cliff-forming coastlines that are rapidly eroding in Norfolk to the east.

Coastal inundation is thus very topical and I continue web maps using available open data.

Part of the climate change risk & mitigation efforts revolve around coastal inundation. I first mentioned this almost a decade ago , when I highlighted flood.firetree.net sea level rise map based on NASA SRTM digital elevation data — more recent example using same is shown on Climate Central Surging Seas Risk Zone Map — Firetree used NASA data to map various sea elevations at 1, 3, 5 etc. m. above current sea level, and every point above each level is left white, while those below are posted blue: Simple yet compelling coastal maps.

I could not, however, source the original data — an issue around openness and web services discussed five years ago — but I did find a version on Esri’s ArcGIS Online. Toggle on the WWF / NASA 4 and 11 m. sea level rise below left, and half of Cambridgeshire in pale yellow is inundated!

Coastal inundation models by Firetree and CReSIS, view original (click all images to enlarge)

When I was doing Arctic sea ice maps, however, I found NGDC-based CReSIS sea level maps. In contrast to Firetree, here a flood model was applied to ETOPO2 digital elevation data in coastal areas (see Overview and credits under here). Desktop mapping showed me a far more conservative coastal inundation of East Anglia: measured from 1 to 6 m contrasts with the 4 and 11 m above sea level. Luck would have it that Kenneth Field had already posted the 1 and 5 m levels of the same data. Toggle those two on in the map above, and you’ll only see the north tip of Cambridgeshire inundated!

CReSIS and Firetree maps were created in 2005 and 2006 respectively, before this became a hot topic. Climate Central’s Risk Zone Maps are today very much in the news. They report NASA’s re-calibration of digital elevation data, released as CoastalDEM 1.1, which is 1–2 m lower than previously thought. They offer also a handy tool to compare old and new inundation models.

Firetree (NASA) and ClimateCentral (legacy & CoastalDEM) flood models for Cambridge & villages north

While the difference doesn’t appear to be huge in the banner illustration, it’s quite apparent in localised maps above. I used the left one to inform Extinction Rebellion locally and the public in general in Cambridge UK: the purported shoreline would lie along the villages where I live just North of Cambridge, or in Cambridge itself depending on the modelled sea level rise. These raised outrageous speculations locally, which I was keen to correct with facts.

These three maps highlight the issues in modelling data to document, interpret and predict the effects of climate change. A patent example was a NASA paper on greening of the earth through CO2 emissions, mitigated by a later one on the human contribution, which were used for political purposes.

I wrote five years ago in Anthropocene Review that map stories provide dynamic visualisations and broaden factually based public understanding. My posting a couple of years ago on flood data interpretation further shows how complex an area this is, as is anything around climate change, I said recently on Medium here. All of these are, however, based on relatively simple maps that can be derived by you, the concerned citizen, to help you sort fact from fiction.

Following ye olde “think globally, act locally”, in addition to contributing maps above, I’m blending such concerns in my Cottenham Open village outreach project with Terry Jackson, and will cooperate with local initiatives such as Cambridgeshire Climate Emergency. Do seek out your local initiatives to address sustainability, community engagement, simple living etc.

Andrew Zolnai

Personal posts on Current Affairs and World Views

Andrew Zolnai

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Citizen of the World, geologist, entrepreneur and volunteered geographer.

Andrew Zolnai

Personal posts on Current Affairs and World Views

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