Around the world, several technologies and processes are being applied to create climate change solutions. For example, some players in the manufacturing industry are working to reduce water waste and carbon emissions4. Numerous countries are now adopting renewable energy sources that perform best in their regions to generate their electricity needs. There’s one more approach that promises great results so far; planting trees to mitigate climate change.
Most people are well aware that human life is dependent on trees. Plants provide the oxygen we breathe as well as food and medicine for us. And trees being amongst the biggest and most numerous do most of this work. But trees serve other significant purposes.
Carbon Dioxide (or CO2) is one of the greenhouse gases responsible for global warming. The major source of the CO2 polluting our atmosphere comes from our use of fossil fuel derivatives to power cars, homes, factories, and more. With the growth of industrialization, more and more CO2 is being released with nowhere to go but up.
Meanwhile, a tree stores carbon during its photosynthesis process. It is estimated that the forest biomass in the EU27 countries contains 9.8 billion tons of carbon (tC). New and regrown forests also seem to be able to absorb more carbon dioxide from the atmosphere than old forests3. With more trees planted, current estimates predict a high rate of success in reducing global warming.
The preservation of forests is directly tied to the availability of clean/drinkable water for communities. This includes both rural and urban areas. For example, New York, one of the most urban cities in the world, sources its drinking water from the Catskill Watershed1; a forested area.
Such water systems around the world are disappearing due to the decline in tree population and forested areas. These trees are either lost to deforestation or left to die of diseases, fires, and insect activity. The resulting effect includes poor soil quality for agriculture and impacts on the scarcity and quality of our drinking water.
By planting trees, we can improve the quality of our water. We can provide tree cover, and restabilize the soil in affected places. More trees will keep our streams, lakes, and rivers thriving.
Climate change is partly responsible for the loss of several animal and plant species that are essential for our eco-systems to flourish. And there are many more at-risk species. As global forests disappear, we can record increasing temperatures, changes in biotic interaction, and lack of protection for wild animals. By planting more trees, we can reverse these effects and protect our wildlife.
Planting trees can have a major impact on environments. It can help to restore degraded watersheds and mend natural cycles (the carbon cycle, the water cycle, the nitrogen cycle, etc.). Often these have been damaged by human activity.
Habitat restoration can help decrease biodiversity loss, and build resilience not only in natural systems but also in human society. Ecosystem restoration is important for humanity moving forward. But this is largely an issue of adaptation, rather than mitigation.
In the big picture of climate change mitigation and adaptation, tree planting plays an important role. Further, tree planting will help us transition to a more sustainable way of life, But as relates solely to greenhouse gas emissions, tree planting is by no means a panacea. The extent to which trees can sequester carbon is a complex issue and one that is often oversimplified.
It is important to understand that a forest is not just a collection of trees. All too often, global tree planting schemes fail to take a holistic approach. Trees are planted like industrial farms, with mono-crop plantations which are unsustainable long term. We need forests, not just trees if we are to truly create resilient landscapes and restore balance moving forward.
By moving blindly forward in planting huge numbers of trees, we may risk covering vast swathes of land with tree plantations that are not ultimately sustainable. Rather than true, rich, biodiverse, resilient forest ecosystems.
Of course, we also have to think about carbon emissions associated with the initiation of tree planting schemes. Where the schemes are taking place and potential societal or environmental negatives of a change of land use can become complex factors.
In certain cases, other landscape management and planting may be more efficacious for carbon sequestration than tree planting. For example, when planted in large groves, bamboo can store four times the amount of CO2 as a stand of trees of similar size5. One hectare of bamboo will sequester 62 tonnes of CO2 per year, while in comparison a young forest covering the same land area will sequester only 15 tonnes.
Carbon farming or agroforestry may also be a more sustainable solution for land use than forestry alone. It will involve tree planting but also integrate other carbon sequestration techniques and more effective land management, which can also help meet human food needs.
Planting trees and restoring habitats is clearly something that we need to do, and urgently, to survive the climate crisis we have created. But it is important to realise that tree planting alone will never be able to keep up with the staggeringly high emissions generated around the globe.
Land use is a hot topic. Land is often in high demand. So dedicating huge swathes of it to tree planting may be impracticable. To put things into perspective, the US – which is one of the world's highest emitters – emitted around 5.8 billion tons of emissions last year.
To tackle that with tree planting alone would involve permanently dedicating an area of land well over twice the size of Texas to forests2. This comes from a study on Negative Emissions Technologies and Reliable Sequestration published by the National Academies of Sciences, Engineering, and Medicine.
Other issues that may arise from planting trees to mitigate climate change include:
There are a huge number of factors that determine the rate of carbon sequestration relating to the climate, the soil, and other environmental characteristics of a tree planting site. Things shift and change over time and measuring efficacy is a challenge.
There is plenty of evidence that many cap-and-trade, carbon offset and carbon credit schemes vastly overestimate the amount of carbon sequestered. The complex picture of the environment, biology and human action (or inaction) mean that schemes are credited with far more carbon-capturing than is actually going on in the real world.
One of the issues with tree planting for carbon offsetting is uncertainty over the time scale of a project. Though planting trees could potentially offset at least some emissions – it definitely is not a short term solution.
Carbon offsetting is now a growing marketing trend in the travel industry. Travel booking sites often promise to donate funds to plant a number of trees for every flight booked on their service.
One company, which will not be named, estimates that the average tree sequestered a little less than one metric ton of CO2. This is around the same as one passenger's share from an average flight purchased through the app. The problem is that the tree would have to be growing for around 40 years to offset this amount. Given varying factors and conditions, the company estimates that it will take around 25 years with the four trees per passenger to offset the emissions from each flight.
It would be folly, therefore, to think that offsetting of this type immediately negates the emissions we generate. The lengthy timescale required to offset carbon emissions with trees, coupled with the urgency of reducing greenhouse gases in our atmosphere makes it clear that tree planting cannot ever be a complete solution to our current crisis.
Of course, it is also incredibly difficult to guarantee that these trees will remain standing. And therefore sequestering carbon for the required period of time. Trees only sequester carbon while growing. Once they die and fall naturally, or are consumed by fire, the carbon they contain simply returns to the atmosphere.
With wildfires rife in Australia, in the Amazon, in the Arctic and elsewhere last year tree planting cannot be viewed as an error-proof, permanent solution. Sadly these climate events look set to grow even worse moving forward,
What is more, there are also uncertainties relating to human activity in newly reforested areas. There is a danger that carbon-sequestering forests could be felled – especially where there is ever-increasing pressure on land and resources.
It is clear that trees will have to play an important role in mitigation and adaptation moving forwards. We have a lot to learn from them, and from the complex interactions of natural systems. But when it comes to combating global greenhouse gas emissions and sequestering carbon, it is clear that they can only serve, in part, as a solution.
There are existing and developing technologies to support trees in sequestering carbon from the atmosphere. These lend new ways to capture carbon through holistic land management and ecosystem restoration. We'll also likely have to use direct-air-capture machines, and other innovative technologies.
We simply cannot afford to be completely dependent on tree planting as a solution. But more importantly, we will have to strive hard, and quickly, to cut off emissions at its source, and transition swiftly to a zero-carbon society.
Planting trees is an important element in climate change mitigation and adaptation. But there is a danger that in diving headlong into tree planting, we can lose sight of the big picture. Tree planting is definitely crucial, but as an article in MIT Technology Review recently noted, it should not become a distraction from the vital task of reducing emissions.
In the article, Jane Flegal, a member of the School for the Future of Innovation in Society at Arizona State University, spoke of the dangers of tree planting schemes fostering a sense of complacency.
Flegal argues that the biggest risk is that people are lulled into a false sense of security by natural-sounding solutions. This confuses us into thinking we are taking more meaningful action than we really are. Flegal also argues that it is a danger for people to view tree planting as a substitute for the sweeping changes we need to make to reduce emissions in the first place.
We have enough evidence to support tree planting as an effort to mitigate climate change. However, the trees we plant today are not for the carbon we emit today. Tree planting is a long-term effort that will mostly help the coming generations.
Reforestation and ecosystem restoration will definitely play a role in tackling our climate crisis. But the level to which these efforts alone can 'save us' is lower than many imagine.
So while we should definitely plant more trees, and work to reforest and conserve our world's woodlands and forests, it is important to realise that they can only ever be part of the solution. Also, we have to make more science-based decisions about where and how trees are planted moving forwards.
|Albert F. Appleton. (2002). How New York City Used an Ecosystem Services Strategy Carried out Through an Urban-Rural Partnership to Preserve the Pristine Quality of Its Drinking Water and Save Billions of Dollars And What Lessons It Teaches about Using Ecosystem Services.|
|National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. https://doi.org/10.17226/25259.|
|Thomas A. M. Pugh, Mats Lindeskog, Benjamin Smith, Benjamin Poulter, Almut Arneth, Vanessa Haverd, Leonardo Calle. (2019). Role of forest regrowth in global carbon sink dynamics. DOI: 10.1073/pnas.1810512116|
|United States Environmental Protection Agency. Using Water Efficiently: Ideas for Industry|
|Designing and Building with Bamboo. Jules J.A. Janssen. Technical University of Eindhoven, Eindhoven, The Netherlands|