Mind blowing potential

From The Guardian:

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.

“This new quantitative evaluation shows [forest] restoration isn’t just one of our climate change solutions, it is overwhelmingly the top one,” said Prof Tom Crowther at the Swiss university ETH Zürich, who led the research. “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.”

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.

[Read more here]

My comments:

1. Note how little of the maps are green.  Only a small proportion of land reforested is needed to remove 2/3rds of the CO₂ mankind has emitted in the last 150 years!
2. Crop land needn't be omitted.  The UK and Irish landscape, a mix of small copses and hedgerows as well as open fields hints at a pattern where the edges of fields (say 10% of the cropland) could be planted to forest
3. As I've mentioned before, the difficult part of reducing emissions to zero is the last 20%, which is agriculture.  Cutting emissions from power generation and transport will be easy.  As long as people want to eat meat (except vat-meat) agricultural emissions will be hard to cut.  But agriculture can still do its bit by planting 10 metre wide (the width of a two lane highway) strips around crop fields.  Although this will need to be subsidised, the cost will be tiny compared to the catastrophic costs of global heating.
4. I've talked about the benefit of an urban canopy here.  An urban canopy can reduce urban temperatures by 4 or 5 degrees C (6.4 to 7.5 degrees F).   Every street should be lined by a dense canopy of trees.  Every piece of spare municipal or state land should be forested.
5. In Australia, most of the native eucalypts are very flammable.  Given rising temperatures and increasing drought, we shouldn't plant inflammable species, because at the first bushfire, all their stored CO₂ will just be released back into the atmosphere.  Brisbane Box Gum isn't inflammable, nor is the Blackwood.  But here in Oz, and in southern California and Mediterranean, perhaps less flammable species like (most) oaks, beeches, birches, will be superior to eucalypts.
6. We can begin right now.  We don't have to wait for electricity generation to transition to 100% carbon-zero, which will take another 15 years.   We don't have to wait until 100% of transport is electric (or maybe, hydrogen-fuelled), which will take another 25 years.  
7. This report fills me with hope.  We can stop global heating.   A mixture of a rapid transition to a green electricity and transport system and of reforesting our landscape will do it.  And meanwhile, we can work on reducing emissions in air travel, iron & steel, cement production and agriculture.  It's doable and feasible, and will cost just a couple of percent of GDP.