Climate Crisis & Trees

You likely sensed that trees are both helpful for the environment and for our health. On our little 5-acre, 7-home garden atrium site, we’ve actually added over 200 trees … without in any way stressing our pocketbooks.  They add beauty and summertime shade, with very little demand for maintenance.  Now, some new research actually quantifies the beneficial effects of trees – without disturbing either farm land or urban land.

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Tree planting ‘has mind-blowing potential’ to tackle climate crisis


Research shows a trillion trees could be planted

to capture huge amount of carbon dioxide


Damian Carrington

The Guardian

4 Jul 2019


Planting billions of trees across the world is by far the biggest and cheapest way to tackle the climate crisis, according to scientists who have made the first calculation of how many more trees could be planted without encroaching on crop land or urban areas.

As trees grow, they absorb and store the carbon dioxide emissions that are driving global heating. New research estimates that a worldwide planting programme could remove two-thirds of all the emissions that have been pumped into the atmosphere by human activities, a figure the scientists describe as “mind-blowing”.

The analysis found there are 1.7bn hectares of treeless land on which 1.2tn native tree saplings would naturally grow. That area is about 11% of all land and equivalent to the size of the US and China combined. Tropical areas could have 100% tree cover, while others would be more sparsely covered, meaning that on average about half the area would be under tree canopy.

The scientists specifically excluded all fields used to grow crops and urban areas from their analysis. But they did include grazing land, on which the researchers say a few trees can also benefit sheep and cattle.

Prof Tom Crowther at the Swiss university ETH Zürich, who led the research, said …


“This new quantitative evaluation

shows [forest] restoration isn’t just

one of our climate change solutions,

it is overwhelmingly the top one.


“What blows my mind is the scale.

I thought restoration would be in

the top 10, but it is overwhelmingly

more powerful than all of the other

climate change solutions proposed.”


Crowther emphasised that it remains vital to reverse the current trends of rising greenhouse gas emissions from fossil fuel burning and forest destruction, and bring them down to zero. He said this is needed to stop the climate crisis becoming even worse and because the forest restoration envisaged would take 50-100 years to have its full effect of removing 200bn tonnes of carbon.

But tree planting is “a climate change solution that doesn’t require President Trump to immediately start believing in climate change, or scientists to come up with technological solutions to draw carbon dioxide out of the atmosphere”, Crowther said.


“It is available now, it is the

cheapest one possible, and every

one of us can get involved.”


Individuals could make a tangible impact by growing trees themselves, donating to forest restoration organisations and avoiding irresponsible companies, he added.

Other scientists agree that carbon will need to be removed from the atmosphere to avoid catastrophic climate impacts and have warned that technological solutions will not work on the vast scale needed.

Jean-François Bastin, also at ETH Zürich, said action was urgently required:


“Governments must now factor [tree

restoration] into their national strategies.”

Christiana Figueres, former UN climate chief and founder of the Global Optimism group, said:


“Finally we have an authoritative assessment

of how much land we can and should cover

with trees without impinging on food produc-

tion or living areas.  This is hugely important

blueprint for governments and private sector.”


René Castro, assistant-director general at the UN Food and Agriculture Organisation, said:


“We now have definitive evidence of

the potential land area for re-growing

forests, where they could exist and

how much carbon they could store.”


The study, published in the journal Science, determines the potential for tree planting but does not address how a global tree planting programme would be paid for and delivered. Crowther said:


“The most effective projects are doing

restoration for 30 US cents a tree. That

means we could restore the 1tn trees

for $300bn [£240bn], though obviously

that means immense efficiency and ef-

fectiveness. But it is by far the cheapest

solution that has ever been proposed.”


He said financial incentives to land owners for tree planting are the only way he sees it happening, but he thinks $300bn would be within reach of a coalition of billionaire philanthropists and the public.

Effective tree-planting could take place across the world, Crowther said:


“The potential is literally everywhere –

the entire globe. In terms of carbon capture,

you get by far your biggest bang for your

buck in the tropics [where canopy cover is

100%] but every one of us can get involved.”


The world’s six biggest nations, Russia, Canada, China, the US, Brazil and Australia, contain half the potential restoration sites.

Tree planting initiatives already exist, including the Bonn Challenge, backed by 48 nations, aimed at restoring 350m hectares of forest by 2030. But the study shows that many of these countries have committed to restore less than half the area that could support new forests. Crowther said …


“This is a new opportunity for those

countries to get it right. Personally,

Brazil would be my dream hotspot to

get it right – that would be spectacular.”


The research is based on the measurement of the tree cover by hundreds of people in 80,000 high-resolution satellite images from Google Earth. Artificial intelligence computing then combined this data with 10 key soil, topography and climate factors to create a global map of where trees could grow.

This showed that about two-thirds of all land – 8.7bn ha – could support forest, and that 5.5bn ha already has trees. Of the 3.2bn ha of treeless land, 1.5bn ha is used for growing food, leaving 1.7bn of potential forest land in areas that were previously degraded or sparsely vegetated.

Joseph Poore, an environmental researcher at the Queen’s College, University of Oxford, said …


“This research is excellent. It presents

an ambitious but essential vision for

climate and biodiversity.”


But he said many of the reforestation areas identified are currently grazed by livestock including, for example, large parts of Ireland.


“Without freeing up the billions of

hectares we use to produce meat and

milk, this ambition is not realizable.”


Crowther said his work predicted just two to three trees per field for most pasture:


“Restoring trees at [low] density is not

mutually exclusive with grazing. In fact

many studies suggest sheep and cattle do

better if there are a few trees in the field.”


Crowther also said the potential to grow trees alongside crops such as coffee, cocoa and berries – called agro-forestry – had not been included in the calculation of tree restoration potential, and neither had hedgerows:


“Our estimate of 0.9 bn hec-

tares [of canopy cover] is

reasonably conservative.”


However, some scientists said the estimated amount of carbon that mass tree planting could suck from the air was too high. Prof Simon Lewis, at University College London, said the carbon already in the land before tree planting was not accounted for and that it takes hundreds of years to achieve maximum storage. He pointed to a scenario from the Intergovernmental Panel on Climate Change 1.5C report of 57bn tonnes of carbon sequestered by new forests this century.

Other scientists said avoiding monoculture plantation forests and respecting local and indigenous people were crucial to ensuring reforestation succeeds in cutting carbon and boosting wildlife.

Earlier research by Crowther’s team calculated that there are currently about 3tn trees in the world, which is about half the number that existed before the rise of human civilisation. Crowther said …


“We still have a net loss of about 10bn trees a year.”


Visit the Crowther Lab website for a tool that enables users to look at particular places and identify the areas for restoration and which tree species are native there.

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In terms of recommendations, begin by identifying places on your home site or near where you walk or drive that could readily support trees. Where an available site is owned by some governmental agency, we’ve found that bureaucratic staff are often resistant to anything that would change their domain – even if it costs them nothing. However, not all agency staff may be that way, so at least ask.


  • Often, a parks & recreation department may welcome additional trees in specific locations.


  • Schools may wish to add trees to enrich their botanical educational programs.


  • Highway departments may also welcome additional trees – perhaps with caution about planting trees that would not create a visibility problem or a falling branch danger as a result of certain storms.


In addition …

Many tree-planting organizations exist. For example, “Tree Sisters” plants three million trees a year, largely in tropical areas that can support a 100% canopy. Their efforts are totally supported by private donations. While most such organizations lie outside the U.S., here are three examples of such organizations within the U.S.:



  • National Tree Foundation. They work mostly in National Forests and National Parks, especially after fires.


  • American Forests. They work in all 50 states, creating resilient forests, from cities to wilderness. Since 1990, they’ve planted 60 million trees.


  • Arbor Day. They “plant, nurture and celebrate trees.” They give trees away to be planted. Since 1972, they have distributed 250 million trees.


Each has a web site. Just Google to get more detail. And then contribute in whatever way feels most comfortable to you.

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