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.
Expert reaction to study looking at trees, carbon storage and climate change
For full text of the criticisms go to this link…
Here are some are shortened extracts:
Dr James Borrell, Researcher at the Royal Botanic Gardens, Kew, said:
“One of the most startling findings is that more than half of forest restoration potential is in just six countries; Russia, the US, Canada, Australia, Brazil and China. A huge responsibility rests on these countries to lead the way if we are to use forest restoration as a tool in the fight against climate change.
“a major criticism of many reforestation plans is that they might compete with other land uses, such as crop land. Here, the authors are explicitly identifying areas for reforestation that exclude cropland and urban areas using a global land cover model. There may however still be some level of conflict with areas used for grazing or livestock.”
Prof Myles Allen, Professor of Geosystem Science, University of Oxford, said:
“In the paper, the authors compare the extra CO2 in the atmosphere with the amount they assess could be stored in forests, but this is misleading, because it neglects the fact that only about 50% of the carbon we release into the atmosphere stays there, the rest being mixed into the near-surface oceans and the like. To date, we have emitted 600 GtC and an additional 300 GtC (50%) of that CO2 remains in the atmosphere. If we had emitted 600 GtC and removed 200 GtC, there would be 200 GtC (50% of 600-200) remaining in the atmosphere. Comparing removal potentials with “atmospheric burden” exaggerates their importance by around a factor of two.
“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. The additional 200 billion tonnes of carbon the study highlights represents less than one third of human-induced carbon dioxide emissions to date, and less than 20 years of emissions at the current rate. So, yes, heroic reforestation can help, but it is time to stop suggesting there is a “nature-based solution” to ongoing fossil fuel use. There isn’t. Sorry.”
Dr Phil Williamson, Honorary Reader, University of East Anglia, said:
Whilst reforestation can undoubtedly assist in achieving net-zero, and subsequently net-negative emissions, it is potentially misleading for the authors to claim that “ecosystem restoration is the most effective solution at our disposal to mitigate climate change”. The most effective solution remains as before: ending emissions, through the worldwide phase-out of fossil fuels within a few decades. Unless that is also done, the newly-planted forests won’t survive for long enough to have the desired effect.”
Prof Simon Lewis, Professor of Global Change Science, UCL, said:
“The estimate that 900 million hectares restoration can store an addition 205 billion tones of carbon is too high and not supported by either previous studies or climate models (e.g. Lewis et al 2019 Science, Arora & Montenegro 2011, Nature Geoscience). The authors forgot to subtract the carbon already on the land and in the soil that was there before any restoration happens. Plus the biome specific carbon storage estimates are too high as they are the end points of hundreds or years of succession, not a couple of decades of forest growth. But, the median estimate from the IPCC 1.5C report scenarios to meet the 1.5C target is 57 billion tones of carbon sequestered by new forests this century, which is certainly possible, if these new forests are adequately protected into the long-term.
“To curb climate change means keeping fossil carbon out of the atmosphere. That means ending the burning of fossil fuels and the dumping of carbon in the atmosphere. New forests can play a role in mopping up some residual carbon emissions, but the only way to stabilise the climate is for greenhouse gas emissions to reach net zero, which means dramatic cuts in emissions from fossil fuels and deforestation.”
Prof Martin Lukac, Professor of Ecosystem Science, University of Reading, said:
“Finally, the paper presents a risk assessment of future changes in potential tree cover. This is the weakest part of the report, and beautifully illustrates the danger of extrapolation – as the authors admit themselves. Looking at their map of the world in 2050, large parts of the Amazon have nearly 100% chance of losing continuous forest cover purely for climatic reasons. We have examples of forest dieback driven by climate change, but I find it very hard to believe that this colossal scale of forest ecosystem disruption can happen in three decades from now.”