Planting billions of trees around the world has been proven to be one of the biggest and cheapest ways of tackling climate change. According to scientists, planting billions of trees is possible and is an effective, nature-based approach to removing CO2 from the atmosphere to mitigate the climate crisis.
Quick facts about planting billions of trees:
- Enough space is available outside of urban and non-forest land requirements
- Treeless land represents 1.7 billion hectares on which 1.2 trillion native tree saplings would naturally grow.
- Treeless land covers about 11% of all land. This is equivalent to the size of the US and China combined.
As trees grow, they absorb and store increasing amounts of atmospheric CO2, a greenhouse gas that is one of the main drivers of global heating. The global impact of an international tree planting program would be transformational, removing almost one-third of all anthropogenic CO2 in the atmosphere today.
The global impact of an international tree planting program would be transformational, removing almost one-third of all anthropogenic CO2 in the atmosphere today.
But trees and forests do so much more than “just” sequestering atmospheric CO2.
Trees help cool our communities by mitigating the heat island effect. Human-built environments, such as buildings, streets, and parking lots, absorb more heat than natural surfaces and radiate this heat throughout the day and night, creating urban heat islands that are often several degrees warmer than nearby rural areas. Trees lower surface and air temperatures through evapotranspiration – the sum of all processes by which water travels from the land to the atmosphere via evaporation and transpiration – and by providing shade. For example, shaded surfaces may be 11 to 25°C cooler than the peak temperatures of unshaded surfaces. In addition, evapotranspiration, combined with shading, can help reduce peak summer temperatures by 1 to 5°C. Trees are most effective as a mitigation strategy when planted strategically around buildings or shade pavement in parking lots and streets. Especially, trees planted on the west and south-facing sides of buildings are very effective.
As mentioned, trees contribute to cooler communities through evapotranspiration in addition to providing shade. Trees do not breathe, but they do something similar, called transpiration. The root system of a tree absorbs water from the soil that travels up through the tree. Transpiration is the process in which some of that water is released back into the atmosphere through tiny pores in the tree’s leaves, called stomata. Evaporated from a liquid with energy from the sun, the released water vapour cools the surrounding air temperature. This cooling effect is potent. For example, a 2016 study from central Montreal confirmed that streets lined with dense urban canopy experienced a lower ground level and cooler air temperatures up to 20 storeys above ground level.
However, trees in an urban environment bring benefits far beyond mitigating urban heat islands. For example, trees that shade buildings decrease the demand for cooling. Also, trees improve stormwater management, reduce runoff, and improve water quality by absorbing and filtering rainwater. Finally, trees enhance the quality of life by providing aesthetic value and habitat for wildlife, removing air pollutants, and reducing noise.
Trees, urban parks, and forests also strengthen the livability of our communities. Urban forests provide a space for kids to play and families to get together. They are a place for learning where children and students and their parents can observe nature and wildlife. There is also plenty of evidence that trees make people feel safer. For example, the presence of large trees in the community reduces crime.
Trees and forests are also powerful contributors to physical and mental health. Research consistently shows that exposure to forests boosts our immune systems. Trees emit airborne chemicals called phytoncides, which they use to protect themselves against insects. When we inhale these phytoncides, our bodies respond by increasing the number and activity of a particular kind of white blood cell. These white blood cells have been cited to kill tumour and virus-infected cells in our bodies. Forests can also improve our lung function. According to the World Health Organization, air pollution kills more than seven million people annually. So ensuring enough trees and forests are located in or around urban and suburban areas to clean our air is paramount.
Spending time in forests also benefits our mental health and how we feel. A growing body of scientific research shows that spending time with trees and in forests benefits our mental health in many ways. For example, walking for 15 minutes in a forest significantly reduces anxiety and depression symptoms compared to walking in an urban setting. Finally, spending time in a forest can also increase our ability to recover from stress.
I hope you agree that the case for planting trees and forests on a large scale is irresistible – an absolute no-brainer! This is especially true because – according to McKinsey’s marginal abatement cost curve – afforestation and reforestation are some of the lowest-cost CO2 sequestration solutions. Also, in July 2022, the OECD and Harvard’s Social Economics Lab published a report on international attitudes towards climate policies that shows that people are most inclined to donate to reforestation causes. So, what are we waiting for?