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Potential of tree planting to combat climate change

Restoration of forests has been considered one of the most effective strategies to mitigate climate change, states a new report published on Friday.

The report, published in the peer-reviewed journal Science, found that there is room on Earth for an extra 0.9 billion hectares of canopy cover; when existing trees, agricultural and urban land were excluded.

This large amount of continuous forest would represent a more than 25% increase in the total forested area and would require in excess of 500 billion trees.

It was also projected these trees have the potential to store 205 billion tonnes of carbon, in areas that would naturally support woodlands and forests. Storage of this magnitude has the potential to cut atmospheric carbon pools by around 25%.

Once the forests are fully matured, they have the potential to capture high amounts of carbon through photosynthesis. Carbon dioxide, water and light are all needed for photosynthesis to occur and thus this is a potential sink for carbon, which is then stored within the trees.

The report said: “Photosynthetic carbon capture by trees is likely to be among our most effective strategies to limit the rise of CO2 concentrations across the globe.”

Senior author of the study, Prof Tom Crowther, said: “Our study shows clearly that forest restoration is the best climate change solution available today and it provides hard evidence to justify investment.”

The scientists found that over 50% of the forest restoration could be found in six countries: Russia, USA, Canada, Australia, Brazil and China. Thus, showing the vital responsibility of many of the world’s leading economies.

Although, climate change is expected to alter the amount of potential tree coverage that can be achieved. If current climate trajectories are not deviated from, the report estimates the global potential coverage may shrink by around 223 million hectares by 2050; with the tropics seeing the highest losses.

New forests take decades to mature and then reach their full potential, showing the short time scale we have to achieve this potential carbon sink.

Therefore, this brings in to question how realistic the restoration goals are, as we are currently unsure how much tree cover will be possible under future climate conditions and where the trees will be able to exist.

There are large uncertainties linked with the modelling used within this paper, due to them relying on machine-learning models extrapolating estimates outside of the existing range of climate circumstance.

Former UN climate chief, Christiana Figueres, an instrumental figure in delivering the Paris climate agreement has welcomed the report.

She was pleased to finally see “an authoritative assessment of how much land we can and should cover with trees without impinging on food production or living areas.”

Others have expressed reservations to the study’s findings:

Prof Myles Allen, University of Oxford, said: "Restoration of trees may be 'among the most effective strategies', but it is very far indeed from 'the best climate change solution available,' and a long way behind reducing fossil fuel emissions to net-zero.”

While Prof Simon Lewis, University College London, was critical of the estimates achieved for the potential storage of carbon.

He said: “The estimate that 900 million hectares restoration can store an addition 205 billion tonnes of carbon is too high and not supported by either previous studies or climate models.”

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