For CO2, it takes a lot of energy to move that soil.
For the soil itself, it brings up subsoil which has microorganisms that work better in low air enviornment (because that is what they are from) and move the near surface microorganisms down below where they don't get the air they need. It also breaks up organic matter making them break down faster (into CO2 if there is O2 available, and the turning just added a bunch). Also all those broken roots no longer hold the soil in place. so the soil will erode much faster.
Erosion is part of it, but even if the soil wouldn't erode the loss of organic matter is still a big deal.
For the soil itself, it brings up subsoil which has microorganisms that work better in low air enviornment (because that is what they are from) and move the near surface microorganisms down below where they don't get the air they need. It also breaks up organic matter making them break down faster (into CO2 if there is O2 available, and the turning just added a bunch). Also all those broken roots no longer hold the soil in place. so the soil will erode much faster.
Erosion is part of it, but even if the soil wouldn't erode the loss of organic matter is still a big deal.