So I was browsing recently, looking at the immense amount of information nestling in our Global knowledge cloud. For all that he is a pillar of a deeply conservative and frankly outdated and socially backward institution I still rather like Charles, the Prince of Wales. He supports a number of causes I hold as important such as the Organic movement and classical structures, be they buildings or collections of cottages arranged harmoniously as a village. Homeopathy, too, I think, though that’s gone very quiet!
Anyway, there exists “The Prince’s Rainforest Trust” and I was checking it out to find their line on rainforest protection and restoration. http://www.rainforestsos.org/about-rainforests/what-is-a-rainforest/
That’s right, they define “Rainforest” as being within the tropics and then paint the standard picture as to how crucial it is that these countries retain their forests as per my previous posting. They suggest “Tropical rainforests absorb nearly a fifth of all man-made carbon dioxide emissions around the world” a bold and rather unsubstantiated statement. It’s maybe derived from the publishings of Dr Simon Lewis (of Leeds University) and colleagues but is plainly just wrong for a number of reasons:
- There are far more forests outside the tropical rainforest region all of which also fix carbon from what is a globally shared resource (the atmosphere, I mean!)
- Retaining this carbon just in said tropical region would add an additional 6.4 tonnes to every hectare of tropical rainforest every year whereas spread globally it is still an extra one tonne per hectare. Even that is hard to gauge over and above natural growth and regrowth. At one hundred mature trees per hectare we’re talking a range of 10 to 64 kilogrammes annual ADDITIONALITY per tree, over and above the natural.
- Tropical rainforest soils vary but can be very carbon poor due to very rapid recycling of dead material unless acid/swamp conditions (mangrove) exist. In temperate and boreal regions there are more often conditions to encourage ground surface and soil accumulation of forest debris so retaining an ever increasing carbon store. Peat bogs act as a very effective “carbon sump” up to the northern steppes.
They are tremendously significant and I do not wish to discount their import but TRF account for only 16% of our total woodland. Like all tree cover it has been greatly reduced over the millennia by human development and is now standing at about 40% of its former maximum. The overall global figure is slightly better than that at around 50%, including all the most northerly boreal regions.
No-one actually knows the destiny of the portion of anthropogenic carbon dioxide released to the atmosphere each year which disappears from the ever growing “ppm” total as portrayed in that uniformly jagged, climbing curve we all know so well. The oceans, which already contain vastly more carbon than all that in the active, terrestrial carbon cycle, and vastly more than the atmosphere ever could, have a complicated temperature dependent relationship with the gas.
Essentially dissolved in the colder, polar waters the carbon dioxide exists in equilibrium within carbonate and bicarbonate chemistry, including the gaseous form. Ocean waters appear to have integral structure and travel – sinking when cool and flowing at some depth to resurface in warmer, tropical locations to replace solar warmed waters carrying equatorial heat away from said situation. For example the North Atlantic Drift emanating from the Sargasso Sea.
This global plumbing system can retain the carbon in deep water for a considerable time – centuries or longer – and different “bodies” of water tend not to mix. I love to quote the kids cartoon “Nemo” on this, as it shows it so clearly, albeit probably without intention! Suffice to say that in polar waters carbon dioxide enters the ocean system and concurrently cooler water surfacing in warm climes release the gas.
There is debate as to the natural balance of such a complex system but base line data derived from ice core analysis such as quoted by Prof William Ruddiman – his book “Plows, Plagues and Petroleum” being a useful starter on extensive academic study – indicate a steady contribution from the oceans to the atmosphere not quite balancing the deposition of carbon in biological carbon sinks (peats, silting to ocean continental shelves). Thus the tendency to a cycle of glacial periods as atmospheric carbon is steadily reduced over thousands of years. (With possible positive feed back and increased speed towards the end of the cycle.)
Now, though, it is suggested that a higher atmospheric carbon dioxide concentration drives increased polar solution of the gas to an unknown period of deep ocean solution. What is its release date? No-one knows, but it will resurface one day!
Otherwise the Northern Steppes increase in bulk. There’s some 4.5 trillion tonnes of permafrosted peats at present but higher global temperature may perversely lead not to more entering this sink but actually increase its rate of decay. My instinct, however, is that this remains a crucial carbon sink at present.
Without a doubt, though, the best carbon sink that we have any control over is to allow new forest creation. Along with advanced new lifestyles which will emerge from this we can look forward to actively compensating for the accumulated terrestrial damage of many millennia as we mop up a good chunk of present carbon emissions and restore woodlands worldwide and not just in the Tropics.