Real Engineering
3 HN recommenders · recommended in 3 months, 2018–2021
12:48 · 2.9M views · Sep 14, 2018
Real Engineering examines whether greening the Sahara could draw down carbon and slow climate change. It concludes that the effort would be enormously costly and that changes in albedo and other effects undercut the climate benefit.
Recommended in tree-planting and carbon removal threads as a sourced explanation of why greening deserts is not a simple climate fix.
4 comments from Hacker News
I recently saw a video about doing this - apparently the desert is actually a really bad option if we want to combat climate change - the core problem is that the desert currently reflects a lot of light from the sun. If we cover it with forest or whatever, then suddenly we adjust the albedo of the earth and absorb more heat, negating some of the impact. Combined with the energy need to pump (and desalinate for trees - your suggestion of kelp would presumably help there) water, etc... make it not really work. Source: this video I recommend watching the video - it explains it better and goes into detail - it cites its own sources.
This video ("Can We Terraform the Sahara to Stop Climate Change?") examines how we might do just that. The conclusion is that it's technically possible (like many things), but the cost far outweighs the benefit. It also introduces new climate risks. this video
Greening deserts is not a good solution for climate change. In fact it might worsen climate change due to albedo changes. A nice video about this: this video
I've been watching waay too many youtube videos about reforestation, agriculture and land management recently and I think I've learned a little from it (links at the end). We no longer have the number of massive herds of animals that used to roam the plains/savannahs grazing, pooing and to a lesser extent escaping from predators. This has meant that the grasslands are no longer trampled on and "fertilised". This has caused the grasses to die back, the soil to degrade, to not hold water and to turn to desert. (see the sahara, the outback, parts of china and the usa). Subsequently we've tried to be really careful with the land and not over graze it etc. which tends to have the opposite effect than what is desired. Now I also looked into reforestation because I thought trees were the answer. Grow trees sequester carbon etc. But it turns out the cost of doing this £/$ and water (desalination) would actually be outweighed by both the albido effect (green trees absorb more sunlight than deserts that reflect it back) and that trees don't really grow fast enough to have the impact required. Getting back to the grasslands, it turns out that when you intensively drive a herd over grasslands the grass initially dies back but the root system expands, the plant grows quickly and sequesters carbon into the ground. It actually builds soil and traps carbon and it does it faster than previously thought. The ground is also more permeable to water so when big storms come it actually soaks up th