November 2021 - COP26
by Nigel Williams
COP26 has highlighted a vast array of issues, but the prominent one in people's minds is the rise in sea level. I have covered this in a previous blog. Since all altitudes on land are measured from mean sea level, every spot height in every country will need to be re-numbered. Every ring contour within 1-2 metres of a summit will need to be removed and possibly replaced with a spot height ending with the number 9. (Spot heights are marked on HARVEY 1:40k and OS 1:50k maps with a black dot and number from air survey. Oddly, OS 1:25k use a brown dot and number for air survey and black for ground Survey).
Until recently, sea level rise has perhaps been talked of in terms of having an end of century impact. Now it seems to be talked of in terms of the next 30 or so years, a much more comprehendible time scale within peoples' life time. Between 2013 and 2021, the rise in sea level has doubled compared to the rise in the period 1993 to 2002. There have been average rises of 4.4 millimetres each year in the last eight years, and it continues to rise.
There are other forces at work that have had less publicity, "glacial isostatic adjustment".
Essentially, as the ice sheets melt the land rebounds. In parts of Alaska, it is estimated to be about 2.5cms per year, 2.5m over the next century, so in part it may reduce the impact of sea level rise. In parts of northern Canada, it is estimated to be around 1.3 metres. Although marginal, I would presume land mass emerging will further contribute to sea level rises.
"Glacial Isostatic adjustment" is the preferred scientific term rather than using the word "rebound" as it appears that glacial loading and unloading is not limited to the upward rebound movement. Scotland is still rebounding and is estimated to rise by around 10cms in the next century, whilst parts of southern England may sink by around 5cms. The country may not be tilting. It seems that displacement of land caused by weight of ice over the north of UK transferred horizontally to push up southern areas of UK, and this is merely a re- adjustment of that. Presumably at some point the adjustment will settle.
It's not just rebound and downward and horizontal crustal motion and changes in global sea level. These processes also affect the Earth's gravity field, induce earthquakes and changes in the Earth's rotation. These other affects are clearly all very subtle. However, judging by news reports it would seem that we are seeing an increase in volcanic activity as evidence.
There are further factors at play, groundwater withdrawals, oil and gas extraction, sand mining and the construction of flood barriers. Groundwater removal in particular can cause the land to sink faster than it would through isostatic rebound alone, because it causes sediments in aquifers to compact together and the land above it to sink. For low lying coastal areas with high populations, the demands on fresh drinking water and irrigation add to the issue. Jakarta for instance was sinking at a staggering 17cms per year. However, these are local issues rather than resulting from global changes. A number of cities around the world, Tokyo for example, have been able stop, and in some cases reverse this through ingenious water management systems.
On a clear day I reckon it may now be possible to see a windfarm from the top of almost every Munro. Whilst they may be contentious, the Geo politics of energy supply is perhaps influencing our acceptance of them. The latest proposals for a couple of around 20 windmill projects in the Highlands are giving a maximum tip of blade height at a staggering 185m!
As one who is working to get a walking cycling path between our village and the local town all of 3km away, it has become apparent that Sustrans are becoming extremely busy whilst struggling to financially meet the demand from communities across Scotland. I hope with Patrick Harvey of the Greens having responsibility for sustainable transport, and the COP26 event, that these projects will come to fruition.
Plans to rewild large areas of the UK are already starting to make a visible impact. I was in the beautiful Glen Feshie the other day. In order to remove a non-native fir plantation a timber lorry track is being constructed across the hill side. I believe it is expected to be removed after some replanting of natural species for re-wilding rather than as a commercial crop.
There are plenty of other examples of changes to the UK infrastructure and landscape that our climate crisis is creating. All of these things are taking place all over the UK. It seems a phenomenal task for our cartographers to keep on top of it all.
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