Nothing can sink any more carbon than its weight plus any bits that fall or get taken and don’t rot. Worse, for most plants most of the weight is water, not carbon-containing organic compounds.
So lawns might be “net” carbon sinks only when compared to the extreme case of leaving the ground bare (or worse, asphalted), but only whilst they’re growing (they don’t really retain any additional carbon after grown and any grass mowned will just return the carbon back to the air when it rots and a lot of it will be Methane, a worse greehouse gas than CO2) and they’re a lot worse at it per unit of area than, say, trees or even just the natural ground cover in just about any land environment but desert.
Nothing can sink any more carbon than its weight plus any bits that fall or get taken and don’t rot. Worse, for most plants most of the weight is water, not carbon-containing organic compounds.
So lawns might be “net” carbon sinks only when compared to the extreme case of leaving the ground bare (or worse, asphalted), but only whilst they’re growing (they don’t really retain any additional carbon after grown and any grass mowned will just return the carbon back to the air when it rots and a lot of it will be Methane, a worse greehouse gas than CO2) and they’re a lot worse at it per unit of area than, say, trees or even just the natural ground cover in just about any land environment but desert.
That’s why I dig up my lawn every year and bury it underground inside sealed plastic bags
I’m doing my part!