Tree-planting - a panacea for global warming or not?

01/02/2024

Tree-planting is offered as a panacea for global warming but, unless handled correctly, it might actually have the opposite effect. Tom Pashby reports Planting trees has entered the public psyche as an overwhelmingly good thing to do. Indeed, the marketing pitch for some products and services now involves the retailer pledging to plant a tree for every x number of units sold. Trees are generally great! They can host massive communities of animals and plants, they can provide a swathe of ecosystem services, such as flood defence and habitat creation, and their fruits and wood can produce economic benefits. And, of course, looking at a tree can improve the viewer’s mental health. However, all this presents an oversimplification of the impacts of tree-planting when you take it to the regional, national or international scale, especially in respect of the climate and biodiversity emergency. Reports from the Intergovernmental Panel on Climate Change (IPCC) include BECCS (bioenergy with carbon capture and storage) as an assumed component of many carbon-budget scenarios. Some of these scenarios involve planting trees in areas that are many times the size of India. Tree-planting in enormous quantities could result in carbon dioxide being sucked out of the atmosphere to allow for continued burning of fossil fuels, to keep us within a 1.5°C global heating scenario, as called for by the Paris Agreement. It’s as good an idea as any other form of geoengineering. Other proposals include huge mirrors in space to reflect the sun’s energy back into space, or pouring iron filings into the ocean to promote the growth of CO2-eating organisms. But they all come with downsides. Just because trees have a good public image doesn’t mean they are perfect. Planting trees on that scale would probably be disastrous for local people and ecosystems. They could easily be monocultures – as we see in the cereal-growing regions of the US and other agricultural countries. Having huge swathes of land dominated by a single type of organism would displace people who live there and would change the local climate. The situation I’ve described is already happening, albeit in a more piecemeal manner. A significant proportion of carbon offsetting uses tree-planting to create carbon credits. If it’s done correctly, tree-planting as a negative emissions technology could be a legitimate form of climate action. However, there are already too many examples of inappropriate species of tree being planted in an inappropriate way and then not looked after long enough for a forest to grow. At least 7,500 trees and shrubs planted next to a new road in Norfolk were found to have died this year because they were put in the ground but then not cared for. It’s not just human malpractice that can lead to tree-planting ending in failure. Extreme weather can wipe out woodlands and leave ground unable to support trees. Uncertainty around whether a tree will grow to maturity after being planted is a major risk when thinking about carbon offsetting on the path to net zero. Carbon offset creators and brokers are aware of this. This is one reason why carbon offsets have a bad name. An individual or an organisation can buy carbon offsets, some of which can be linked to a physical instance of a carbon sink, such as a new forest, and then that forest can be wiped out, at which point the buyer of the carbon offset may have already put more carbon dioxide into the atmosphere. It’s not just the physical risk to trees that creates problems for those in the offsetting sector. There’s also administrative and financial risk. One tree-planting project can be so far removed from the final buyer, both in terms of geographical distance and supply chain bureaucracy, that the trees (which might die) could be counted more than once towards a carbon-accounting balance sheet. The carbon credit market is growing, but I worry about the inclusion of BECCS in IPCC scenarios, because it sends a message to governments and corporations that tree-planting might be the silver bullet that saves us from a dangerously heated world. It takes decades for trees to grow to maturity. There’s an old saying that the best time to plant a tree was yesterday. And that is true. But we need to make sure we are planting them in a responsible way and with due care and attention given to local communities of people and wildlife. Tom Pashby AIEMA is a freelance journalist