Eli5: increased CO2 = Increased vegetation, shrinking sarhara, really?


When I was at school there was a process called desertification occurring causing increasing desert. Now it seems the opposite is happening. Which might be good. But I wonder is the world getting greener because of the increased CO2 or is it because the ice is melting and that land is getting more green?

Or is this all misinformation and have I been misled/misunderstood?

In: Earth Science

The world is overall not getting greener, the green parts are just shifting around because of disrupted air currents. This is *incredibly bad* because we need the parts that are green and fertile now, (farms) to stay that way. The more shifting that happens, the worse famine gets. It’s also bad for the other things currently living in whatever areas become desertified.

Desertification isn’t because plants don’t have enough CO2. It’s because when plants get cleared out (usually by human activity), they can no longer hold topsoil in place. Topsoil retains moisture and gives plants a chance to start growing, so it’s necessary to grow most new plants. Once the topsoil blows away in the wind, plants can no longer establish themselves there, which means there’s no way to make new topsoil, and so you have a stable, permanent patch of desert. Adding extra CO2 does nothing to stop this.

Desertification still happens, it wasn’t just for that few years you were at school. And there is indeed satellite evidence of some regions of the southern sub-Sahara area becoming more green in the past few decades. However, only speculative explanations have been proposed for this so far and the most reliable sources I could find were speculating that it’s due to recovery from drought and improvement in farming techniques, not a global un-desertification process.

This makes biological sense too. The limiting factor for plants growing in deserts is water availability, and water is necessary for photosynthesis. You could increase CO2 levels ten-fold and if the water availability remained the same, plants would continue to grow at the exact same speed. The deserts have been getting drier because of the expansion of the Hadley cells that cause them (equatorial bubbles of air that lose all their water over the equator and then flow away from it as very dry air with no rain to drop), it’s just that this one region has had more rainfall in the past few decades than it had in the earlier photos of the record.