Trees to the Rescue

Planting a trillion trees would remove from the atmosphere two thirds of the emissions put into it by human activity.

A Tree Aid project

It would be by far the most powerful method for slowing global heating and the consequent disasters.  It is also by far the cheapest, does not need to wait for technological breakthroughs, and individuals can help it along.

This is the conclusion of the first thorough survey of the world’s areas that could be tree-planted.  The research was led by Professor Tom Crowther of ETH (Eidgenössische Technische Hochschule, the Federal Institute of Technology, at Zürich in Switzerland).  It was published in the authoritative journal Science, and welcomed and endorsed by other scientists.

The researchers measured tree cover in 80,000 high-resolution satellite images.  They used soil and climate data to compute the tree-growability of each area.

Some numbers that I gleaned and sorted into logical order:

3 trillion (3,000,000,000,000) trees in the world now.

6 trillion (6,000,000,000,000) trees before humans started destroying them, mainly with agriculture; the world’s natural tree population in the present geological age.

10 billion (10,000,000,000) trees are being lost per year (the net loss, allowing for planting that is going on).

8.7 billion (8,700,000,000) hectares of the world’s land surface (2/3 of it) is able to support trees.

5.5 billion (5,500,000,000) hectares of that now has trees.

3.2 billion (3,200,000,000) hectares of it, therefore, is treeless.

1.5 billion (1,500,000,000) hectares of that is used by humans for food-growing and residence and “infrastructure.”

1.7 billion (1,700,000,000) hectares, therefore, is the area that is now treeless – degraded or sparsely vegetated – and could be tree-planted.  It is about 11% of the land surface; the size of the USA and China combined.

1.2 trillion (1,200,000,000,000) native trees could be planted on those areas.  I’ll call that the Tree Archipelago.

200 billion (200,000,000,000) tonnes of carbon would be absorbed out of the atmosphere by that number of trees.

4.2 trillion (4,2000,000,000,000) trees would then be in the world; 70% of the pre-human tree population.

(These figures obviously are rough.  There must be an assumption as to how “tree” is defined, since so many seedlings and saplings in forests die.  The words “billion” and “trillion” now have their “short-scale” meanings in Britain as well as America, explained in my Portrait of a Million, yet they remain dangerously ambiguous.  Abbreviations like “1tn” look dangerously tiny.  That’s why I spell them out.)

Excluded from the Forest Archipelago are all cropland and all urban land – all areas that we now use to grow vegetable food or to live on.

Pasture land is slightly included.  At least some of it can be used for sparse tree-planting.  “Many studies suggest” that grazing animals such as cattle and sheep do better if there are two or three trees in a field.

Not included in the calculation were hedgerows, along which so many trees can stand.  Nor “agro-forestry”: the beneficial growing of trees alongside crops such as berries, coffee, and cocoa.  Increasing these would help.

The scale of the Forest Archipelago’s benefit was unexpected and astonishing to the researchers themselves.  They had thought it would be among the top ten best climate-change solutions.    But it is “overwhelmingly” the most powerful.

It certainly does not mean that we can cease trying to reduce greenhouse-gas emissions, or tolerate the ongoing destruction of forests.  The baseline over which the Forest Archipelago is an improvement is the present number of trees and the present amount of carbon in the atmosphere.  Obviously, if old forests keep on being cut, and emissions aren’t reduced, the Forest Archipelago is in a race against them; will take longer to be achieved, or will never be achieved.

The full Forest Archipelago may take fifty to a hundred years to achieve.  It depends on human cooperation.

Sample maps that you can see in the Guardian article show what the Forest Archipelago is like – myriad dots scattered across all lands.  There are noticeable densities of them in, for instance, Texas, the Appalachian mountains, Ireland, the Alps, eastern Australia.  But there are some of them almost everywhere!

The calculations took account of differing tree densities in climates.  They are higher in the tropics, where tree “canopies” can be 100% – more foliage per hectare.

There are existing reforestation programs.  The Bonn Challenge, backed by Germany and begun in 2011, aims to restore 150 million hectares of the world’s degraded and deforested land.

Experience like this shows that the cost per tree is $0.30.  For a trillion trees, that’s $300 billion [(£240 billion).  The same average efficiency is not likely to be achieved by the vast mixed activity of the Forest Archipelago.

Yet the cost is far less than for any other large solution, such as carbon capture or space mirrors.  Those depend on technologies that have problems and will not work on the scale required.  The Forest Archipelago needs no sophisticated technology,

The ETH researchers did not speculate on how this global project might be planned and funded.  But they point out that “$300 billion would be within reach of a coalition of billionaire philanthropists and the public” – a consortium of existing organizations? – some crowd-funding?

Governments don’t have to be relied on.  But those that are not in climate-change denial could help, with “financial incentives to land owners for tree planting.”

And individuals can participate, on the fringes and in the little glades of the Forest Archipelago. We can plant trees in whatever small or large bits of land we’re lucky to lown (as my son and daughter do. and contribute to tree charities – I am now doubling the monthly standing-order donation I’ve made since 2004 to Tree Aid.

(Wherever you live you can support TreeAid, which grows trees in dryland Africa.  There are also Trees for the Future, and One Tree Planted.)

Notice that the trees planted would be native to their regions, able to flourish there.  Not monocultures of pine or eucalyptus.  As scientists from other fields commented, it will be crucial to respect the traditions of local and indigenous people.  That is likely to help restore biodiversity.

There is a “tool” by which you could look at any selected area – and the tree species native to it.

If the Forest Archipelago is achieved in full, and if the present human-used area – farmed and occupied – grows not too much, the result would be a world in which both climate and biodiversity would be stabilized or would even begin to return toward their better pre-industrial states.

But I think it could be even better than that.  So much agricultural land is not needed.  The Forest Archipelago is compatible with vertical farming.

Vertical farming – inside cities, in greenhouse buildings but also, like tree-planting, contributable to by individuals – could mean that the bulk of the vast areas that humanity has converted into fields could return to nature.

I won’t live to see it.  But my present happiness is strongly affected by either future  possibility:

That the world will be one in which civilization is a forgotten luxury, because inhabitants of the survivable countries battle to keep out desperate hordes from the torrid lands of hunger and thirst.

Or that civilizations of probably happier humans flourish in islands amid green landscapes of richer natural diversity.

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