How land-use change affects the climate

When people talk about greenhouse gas emissions, one of the sectors often mentioned is land-use change. And while the energy sector is responsible for almost three-quarters of the emissions, agriculture, forestry, and land use make up another 18.4%. In this article, I plan to finally shed some light on what this cryptic land-use change actually is.

Agriculture, forestry, and land-use change make up way too much of our stupid greenhouse-gas pie diagram. But if you ask people, what land-use change actually is, most draw a blank or answer with a variation of "Um, changes to the land?" I mean, yeah, sure. Not incorrect, but also a bit too vague for my liking.

Some people talk about land-use change, some people just go with land use, some people talk about land-cover change. There are different acronyms like LCLUC, LULUCF, or LULUCC, too, but as "lulu" is the child term for a penis in German, I won't be using LULUCC for this article to spare myself some childish giggling fits. We'll go with land-use change.

To use the definition of ScienceDirect, "Land use change is a process by which human activities transform the natural landscape, referring to how land has been used, usually emphasizing the functional role of land for economic activities."

The problem is that it's pretty hard to actually figure out what the emissions of land-use change are, as you need to untangle the figures from the carbon-sinking capabilities of the natural world.

The essential problem is this: you've got a real forest. When I say real forest, I mean one that hasn't been cut down and replanted by men but has been left to flourish, a forest with ancient trees, younger trees, underbrush, and all the little critters that live in the soil. So, you've got a real forest. This forest acts as a carbon sink. Animals and other plants use the old growth as their habitat. It's a give and take of nutrients, an ecosystem in balance. Now, enter humans. You know how good we humans are at fucking this shit up. We roll in with our heavy machines and take down the trees, especially the older ones with a lot of wood. We compact the soil with our machines, considerably modifying the soil structural characteristics along with a reduction in macro-porosity and thus water retention abilities. The strong compaction of the wheel tracks reduces the water conductivity to 10% of the original level. Not to mention all the tiny organisms that no longer have a habitat to inhabit. Fewer trees also mean less carbon dioxide sequestration. Often, we then add agriculture with heavy pesticide use or ruminating animals to get us from a carbon sink to a carbon-emitting land area.

Even in areas where the forest is cut down and then replaced with young trees, the ability of the forest to store carbon is greatly reduced. While it is true that older trees are less efficient at photosynthesis, their sheer mass makes up for that slight inefficiency. It's another lovely example of an exponential function. I love exponential functions. Seriously, if more people were able to get exponential effects, we'd be in a better place. If an average tree grows to 10 times it's size, it gets 100 times as many leaves. The leaves are the main factor for the tree's photosynthetic ability, so having a shitton of leaves means a shitton of photosynthesis.

Similarly, tall trees convert more carbon into oxygen than shorter trees. This is both due to what I just said and to the fact that they just get more light at the top of the canopy and thus more energy for photosynthesis.

Deforestation, the soil disturbance of agriculture, and biomass burning (such as with controlled burns of forests) add a vast amount of carbon dioxide to the atmosphere (and thus the ocean). But how bad is this problem?

An evergreen tropical forest stores about 202 tonnes of carbon per hectare and even a deciduous forest, so a forest with seasons, stores about half of that. On the other end of the spectrum, cropland only stores between 8 and 30 tonnes per hectare. We don't even want to talk about grazing land for farting cows. But even if the deforested land is used for a plantation, it can only maintain between 30 and 90 tonnes of carbon per hectare.

And as I said, if the land is used for agriculture or plantations, we are introducing more than just a lack of old growth. Fertilizers contain a lot of nitrogen oxide, a potent greenhouse gas. The fertilizers also run off into rivers and lakes or get washed into the ocean where the extra nutrients lead to algae blooms, but that's a topic for another day. Disturbing the soil during tilling releases more of the carbon stored in the soils. And flooding rice fields emits methane, another potent greenhouse gas. So no matter what you put on the land you just deforested, it only gets worse. And I don't care the land is still able to maintain maybe half of the carbon sequestration as a plantation, the scale leads all the way to ruminating animals and actually adding greenhouse gasses instead of sequestering them. And in any case, we are worse off than before.

And while I agree that it is important to have food and a roof over your head, I believe that we need to be more careful with where we put our cities and fields. We need to get creative with how to grow food, reduce animal consumption (remember, 70% of crops like soy, corn, wheat, and rice go into animal feed), and stop destroying our remaining few untouched forest areas for profit and overconsumption.

So, what can you do?

I feel like I keep repeating the same advice, but as it's very important advice, I will keep repeating it:

Don't waste resources. Water and food have a much higher cost than what you pay for them. It takes a hundred liters of water to grow one banana. Trees were felled and meadows mowed to make room for that cow you had for dinner. More trees were felled, often in irresponsible logging operations, to make that cheap IKEA table. Buy used where you can. But from better sources where you can.

And as always, educate yourself, educate others, and vote both at the booth and with your dollar when you purchase items at the grocery store. When it comes to deforestation, our old friend palm oil is a pretty good example of an ingredient to avoid. Palm oil is grown in monoculture, often at the cost of old growth rain forest.

Mentioned in this article:

Kate Hildenbrand

Kate Hildenbrand

Kate Hildenbrand is the writer behind the essays here, author of fiction novels, the creator of the Kate Hildenbrand podcast, and a student of marine ecology. At least, that's her on the surface.