I agree lawns are dumb but from an environmental perspective they can be net carbon sinks, which I found surprising. Though they are still bad for other environmental reasons.
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.
Asphalt is definitely a carbon sink though since it’s a petroleum product!
It is if one does not count the heavy hydrocarbons taken from raw crude and used to make asphalt in the maths of carbon pulled out of the Earth originally when the oil is pumped out - in other words, if one blames the lighter stuff used in fuel for the actual oil extraction and then just goes with “well, now that we have this stuff out, might as well use the heavy stuff for asphalt”.
Otherwise its adds up to a carbon source because even though the fraction of crude oil that ends up used for asphalt has it’s extraction from underground sources offset by that stuff ending up back on the ground as asphalt, the various processes between it coming out of the ground and it ending back on the ground do emit CO2 and some light hydrocarbons.
Sure, nowhere as bad as fuel and gas, but still a net negative.
I mean if you want to talk about sequestering carbon, there’s all sorts of natural lawn options that aren’t actively planting an invasive species that has proven to be really bad at doing any sort of water filtration or absorption. In fact, I’d wager that planting (and letting grow) prairie or whatever your native biome supports probably sequesters more carbon, assuming your native ecosystems aren’t straight up desert. Even if they are, you’re now using so much less water that it’s a huge net win there.
