The Role of Vegetation and Soil Organic Matter in Regulating Climate
On scorching days like these, as new temperature records are being broken across the country, it's easy to feel powerless in the face of global warming. When we talk about climate change, most discussions focus on reducing CO₂ and other greenhouse gases, since they act like a blanket that traps heat in the atmosphere. That's certainly true. However, we often focus solely on removing that "blanket" by cutting emissions, while overlooking another critical issue: how we are changing the way the Earth's surface absorbs and processes solar energy.
Over the past few decades, we have dramatically and rapidly increased the amount of heat accumulating at the Earth's surface. What I'm referring to is the way we use and manage land. Deforestation, urban expansion, and covering the ground with concrete have disrupted the natural mechanisms the Earth relies on to cool itself.
This warming occurs when sunlight reaches the ground and is converted into heat. How much heat builds up depends largely on the moisture and vegetation covering the land. When soil is dry, low in organic matter, sparsely vegetated, or sealed beneath concrete, most of the sun's energy is converted into sensible heat, directly warming the surrounding air. In contrast, when soil is moist and covered by deep-rooted vegetation and natural ground cover, much of that energy is used for evaporation and transpiration (latent heat), which provides a powerful cooling effect.
One of the natural systems we've disrupted is the small water cycle. When land is covered with diverse, multi-layered vegetation and deep-rooted plants, the soil is able to retain water. Plants draw that water up through their roots and release it back into the atmosphere through evapotranspiration. This process cools the environment in much the same way that sweating cools the human body. In addition, the water vapour released by plants helps form clouds and rainfall, further cooling the landscape. This is why rainforests are capable of generating much of their own rainfall.
The clouds created through this process also reflect a portion of incoming sunlight back into space through the albedo effect, further reducing the amount of heat absorbed by the Earth's surface.
A key factor that keeps this entire system functioning is soil organic matter (SOM). Organic matter greatly increases the soil's ability to retain water while maintaining healthy soil structure and a thriving microbial community. For every 1% increase in soil organic matter, the soil can store up to 95,000 litres of additional water per hectare, transforming heavy rainfall from a flooding hazard into a valuable water reserve.
When soil organic matter is lost, soils become dry, compacted, and unable to absorb rainfall effectively. Instead of infiltrating the ground to replenish groundwater supplies, rainwater runs off the surface, carrying away fertile topsoil and contributing to erosion, flooding, and landslides.
This process can be seen remarkably clearly in Australia's accidental Rabbit-Proof Fence Experiment. More than a century ago, Australia built a 3,256-kilometre rabbit-proof fence to stop the spread of invasive rabbits introduced by European settlers. Although the enormous fence ultimately failed to stop the rabbits, it unintentionally created a sharp boundary limiting the expansion of mechanised agriculture.
On one side of the fence, native vegetation was repeatedly cleared to grow seasonal wheat. On the other side, native ecosystems remained largely intact.
Years later, the contrast between the two sides became impossible to ignore. The untouched side remained green and rich in biodiversity, while the agricultural side became noticeably hotter and drier, with fewer clouds and 20–30% less rainfall than the naturally vegetated landscape.
In my view, we don't necessarily need to rewild the entire planet. We can still produce food while protecting soils and vegetation through sustainable farming practices. Intercropping, planting diverse species, preserving large trees and ground cover, creating multi-layered planting systems, applying biochar, making compost, and regularly pruning biomass are all effective ways to maintain high levels of soil organic matter and keep the water cycle functioning.
These practices also have the added benefit of improving crop productivity while reducing farming costs over the long term.
These principles should also be applied in our cities. We need to plant and protect large trees, preserve as much vegetation as possible, and create biodiverse green spaces throughout urban areas.
Doing so will reduce the amount of heat accumulating at the Earth's surface and help lessen the impacts of climate change. This doesn't mean we no longer need to reduce greenhouse gas emissions. Rather, it gives us another practical perspective—and another set of solutions—so we can tackle this challenge from multiple angles.
Finally, I'd like to emphasise that restoring vegetation and repairing the water cycle is only one part of the solution. It must go hand in hand with reducing global CO₂ emissions, since greenhouse gases continue to trap heat higher in the atmosphere. But if we focus only on cutting emissions while allowing our soils to continue degrading, we will lose one of the Earth's most effective natural cooling systems.
"The best time to plant a tree was 20 years ago. The second best time is now."
References
The Impact of Changed Land Cover on the Regional Climate of Southwest Western Australia
https://www.researchgate.net/publication/228849065_The_impact_of...The Impact of Land Management Change on Rainfall and Cloud Formation in Australia
https://agupubs.onlinelibrary.wiley.com/.../2010JD014950Ground Breaking: Soil Security and Climate Change by soil scientist Phil Mulvey.
https://onesearch.slq.qld.gov.au/discovery/fulldisplay?docid=alma99184350858602061
