How good soil helps our climate
We talk a lot about carbon these days. Too much up there, not enough under our feet. And yes, it’s super important to draw carbon from the atmosphere (where there’s an excess) and fix it into the ground instead. It’s fantastic, actually.
But, there’s more to carbon than the value of simply taking it out of the atmosphere. The role it plays within the soil is what’s really important, for a few different reasons.
How does carbon in the ground cool the atmosphere?
Let’s bring it back to global warming and the greenhouse effect. The earth receives a certain amount of heat from the sun everyday, and to maintain a steady temperature, it has to radiate that back into space. Kinda like a dog panting. The greenhouse effect is basically when this cool-down system isn’t 100% efficient, and heat stays trapped in the atmosphere.
This has been fundamental to the development of life on earth, but, as we all know, it is getting out of hand (climate change).
It’s not all about C02
Rising levels of C02 in the atmosphere get a lot of the blame for this greenhouse effect, but they actually only contribute to about 4% of the planet’s heat dynamics. Water vapour, on the other hand, is responsible for 85% of them. To put it simply, the more water in the soil, the better it can hold onto heat, and this is where soil carbon comes back into play.
Soil that’s rich in carbon has more organic matter - roots, humus and organisms like bacteria and fungi. These wee organisms do more than their fair share of work, and part of that is creating a strong soil structure.
A strong sponge can hold more water
We can think of organic matter as the building blocks for a healthy soil food web, one with strength and structure and lots of space in between - one that’s designed perfectly to hold on to heaps of water. Like a sponge! We went into the nitty gritty of how this works in our post about healthy soil ecosystems.
But for now, let’s dive into why that matters. At the moment, most soil on the planet has about 0.8 % organic matter, which can hold roughly 10 days of water. If we increased that to 3%, that same soil could hold water for 100-150 days. That’s a hefty increase. Soil with more carbon and therefore a greater water capacity is like a great big sponge.
So why does this matter?
There are many, many reasons we want our soil to hold more water. Firstly, if we’re thinking about the greenhouse effect, the more hydrated soil covers the land, the more solar energy can be absorbed. This keeps that heat in the ground and out of the atmosphere.
Now let’s look at what can happen if our soil sponge only has enough carbon to hold 10 days worth of water:
Any more rain will lead to what we call run-off. It’s pretty self-explanatory - the water runs off the soil, taking the carbon-rich top layer away and leaving potential flooding and a carbonless desert.
When this top-soil layer is lost it’s called erodification, and without a carbon sponge, the soil can’t absorb more water.
No moisture in the soil means no moisture to stop the spread of bushfires.
Basically a whole lot of stuff we don’t want, but it’s happening to farmers all over the world, and could be saved by a small increase of organic matter in the soil. Remember, upping it from 0.8% to 3% is the difference between 10 and over 100 days of water storage.
So how can we increase soil carbon?
Compost! When you add compost, you’re feeding your soil organic matter. Read more about the benefits of composting here.
Ditch the chemicals to keep your soil’s organic matter alive and kicking
Increase biodiversity (by having lots of different types of organic matter)
Keep your soil planted all year round to help build up that carbon sponge
Avoid tilling, which can compact and break down soil structure
So yes, the mighty carbon in our soil does so much more than being ‘out of the atmosphere’. With its complex relationship to water, it has the potential to play a powerful part in slowing or reversing climate change.
As guardians of the soil beneath us, we too have a big role to play. By nourishing it with organic matter, we can hydrate the soil that covers the land and help to cool our planet.
