Is my lawn a net CO[sub]2[/sub] sink or source, after taking everything into account? The communities around us have been having water rationing because of hot weather and lack of rainfall lately, but here in Ann Arbor, MI, we have our own water system, and don’t have any restrictions. I’ve been feeling a little guilty having a green lawn, but then I thought, “Hey! Maybe I’m actually helping the planet!”.
Certainly, the lawn absorbs CO[sub]2[/sub], but then I have to mow it. I use an electric mower, so some coal plant has to work a bit harder, putting out more CO[sub]2[/sub]. Is this better than a gas powered mower (I’m not going to use a push mower!) I use milorganite for fertilzer, if that makes a difference.
My lawn is moderately green, but could be greener if it was watered more. Should I or shouldn’t I?
Tough call. Watering it would mean that you are diverting water from the farmlands, which means less crops, and thus less surplus for export, resulting in reduced profits for farmers, unemployed food processors and shippers, not to mention more world hunger than there could be.
It also means that you would be making the grass grow, and as you mentioned, using electric or gas to mow it will increase CO2 levels, however, even using a push mower will mean exertion on your part, again increasing CO2 levels while at the same time reducing the amount of surface area of the grass that could absorb that additional CO2. So it is self defeating. Not mowing the grass at all would give the impression that you wasted all that water as you really aren’t concerned with the visual appeal of your lawn, and should have just let the water go to the farmlands instead.
Not watering the grass however, would give the impression that you simply do not care about global warming or the survival of the planet, in which case you, like George W., would be held personally accountable for failing to save the planet from the grip of the greenhouse.
Just a guess but I don’t think your lawn counts as much of a CO[sub]2[/sub] sink. Sure, every little bit counts but my guess is you create more CO[sub]2[/sub] than the grass eats just by maintaining it (mowing and so on…got a power weed whacker?).
Also, don’t forget that watering your lawn takes energy as well. It needs to be pumped out of wherever it comes from, filtered and pumped to you.
In addition the fertilizer you use adds CO[sub]2[/sub] to the atmosphere. I don’t know how it is manufactured but the packaging and shipping of all that stuff takes energy if nothing else.
All in all I’d say your best bet for a CO[sub]2[/sub] sink would be to leave your lawn alone and let it grow wild (or die) on its own.
The CO2 taken out of the air has to go somewhere. In the case of your lawn, it gets sequestered in the leaves and roots of your grass. If you cut your grass, the CO2 in the clippings will eventually go right back into the atmosphere, unless you bury them in a deep, deep hole. In keeping a healthy, trimmed lawn, the amount of trapped CO2 will stay about constant, but fertilizing, weeding, cutting and watering will all cost CO2, as other posters have said. Therefore, keeping a lawn will contribute to global warming.
If you don’t water it and let it grow wild, you might end up having to burn off all the dead thatch. Again, CO2 is released into the air.
For the good of the planet, you should bury the whole thing under a huge concrete slab.
Remember that plants are just a temperary storage for CO2. They will eventually decay and release that back into the atmosphere. The only true CO2 sink on this planet of any size is in the ocean (IIRC creating of limestone). Maintaining a lawn is an evironmental disaster.
I’m in a new subdivision, where the developer scraped off the topsoil, so there isn’t much organic matter in the soil (I meant to mention this in the OP). Worms will eat the grass clippings and Milorganite (so I’m told) and distribute it throughout the top foot or so of the ground. So for a while, at least, I will be sequestering CO[sub]2[/sub].
What everyone’s forgotten so far is that the soil itself is a significant carbon pool. There would be far more carbon stored in the soil under your lawn than you’ll ever get in the lawn itself. The size of this pool is dependant on many factors, particularly soil type and density but it will be significant anywhere.
Generally speaking if you want to reduce CO2 emissions you should water your lawn. If you don’t water your lawn the grass dies and as a result no more carbon is entering the soil carbon pool. The soil carbon will continue to be mineralised by bacteria and since we have no input the net flux is out of the pool. This has been demomstarted pretty conclusively in agricultural land and would apply equally to suburban lawns. Added to this a lack of water will reduce the amount of anaerobic breakdown occuring, meaning less resistant humus is being reduced and again increasing carbon loss from the soil.
The rate of turnover from the above-ground part of the carbon cycle of your lawn is so rapid that the only practical only advantage to not watering is that you need to mow less. However this would be small beans indeed compared to the probable carbon loss from even 1/10 acre of lawn.
So water with a clear conscience.