A Unique thought on Trees

If you have seen this thought elsewhere, please let me know, and I’ll take the word ‘unique’ out of the header.

So I like the idea that the world is getting warmer, that it is overall beneficial and humans are responsible. Beneficial because more carbon dioxide means more warmth, higher levels of flora growth, less spent on central heating and clothing and the possibility of getting a decent cherry tree to grow north of the Tees. The latest models imply global wind speeds are rising slightly so more output from wind farms and reduced desertification as clouds carry more moisture and carry it further inland. So a greener earth.

The two main downsides are pests migrating northwards ( this is a rich world problem, so we should use a carbon tax for research to mitigate this ) and rising sea-level.

But roughly what effect does planting a tree have on sea-level? A tree contains a lot of water bound up in its structure, cellulose, sap, lignin, other organics and water itself. Let’s suppose every tree contains as much water content as this oak, about 6.5 tonnes, based on the difference given between its above ground living weight and its dead weight. If the tree had never existed that water content might otherwise have run downhill to the sea and raised the sea-level by a  micron or so. According to the Wikipedia tree entry there are 3tn trees in the world and let’s suppose we could magic into existence an extra 1% of that and each are as fabulous as that earlier oak tree – what would be the effect on water retention and hence water not making it to the sea?

30 billion trees, each retaining 6.5 cubic metres of water ( density of water is 1 ) is just under 200 billion cubic metres of water. Stop that amount of water from reaching the Oceans which cover about 362 million square kilometres of Earth, and you’ve reduced sea-level by about 0.6 of a millimetre. That’s about 1/3rd of the annual rise occurring at the moment. Not taken into account here is the water retained in tree roots, soil, and in the moisture of the surrounding air. On the other hand the oak linked to above is not your typical tree. So this 0.6mm estimate can easily be rubbished.

There are many reasons to want more trees, but holding back sea-level rise because of their internal water retention could be another one.


A lot of upland and northern Britain looks like this, so the UK itself could start to add 1% a year of tree cover for a great many years ( funding and people-power required of course ).