People often tout planting trees as a way to combat climate change. It's not wrong. Plants perform photosynthesis to convert light energy into sugars and other molecules to store it for later use. In that process, they also remove CO2 from the atmosphere, which is one of the main greenhouse gases causing climate change. The more trees and other plants there are, the more CO2 is removed from Earth's atmosphere, and the slower it warms up.
Why is it not about planting trees, then?
Because, it's about the land. The issue is not that we have too few trees. The issue is that we don't have enough land where they can grow. Look at this chart:
We use almost half of the habitable land on Earth to make food from animals. As you can see, 77% of agriculture land is used for livestock. However, that land only provides 18% of the global calories and 37% of the global proteins. Something's amiss.
Critics of tree planting often raise the point that planting trees will emit much more greenhouse gases in the form of fertilizers, energy, and so on than the trees will sequester, because they need to be planted on barren land like deserts. Of course, it won't make sense to plant California redwoods in the Sahara desert. Then again, where else would you plant it? If you look at the chart above, the habitable land is already occupied.
We need to free up land. Not only to have more place for trees to grow, but also to restore animal and plant species that are now at the brink of extinction.
Raising animals to eat their meat and use their milk is an awuflly inefficient way of producing food. The graph above makes that abundantly clear, but it's also basic common sense: Why not eat the plant directly instead of feeding it to a cow and eating the cow?
One study in Nature estimates that if we stopped raising animals for food, the wildlife and nature that would grow back on the freed up land area would sequestrate 332–547 Gt of carbon dioxide until 2050. That's between 99% and 163% of the CO2 emissions budget put forward by the IPCC.
This wouldn't require us to try impossible things like planting trees in the desert. It wouldn't even cost more or require the invention of a new futuristic technology. In fact, it would cost less and help fighting climate change, stop polluting freshwaters, decrease the likelihood of future zoonotic pandemics like COVID-19 and restore biodiversity. It would also offer much more space for us humans to go to and enjoy the beauty and benefits of nature.
The best thing about this is that we wouldn't even necessarily need to actively plant trees. Nature is excellent at restoring the balance of Earth if we only give it the space to do so.