6 ms·

The carbon emitted by the lawnmower came out of the ground, where it had been for millions of years. Net effect, more carbon in the atmosphere. The carbon in

by seanc 17y ago

The carbon emitted by the lawnmower came out of the ground, where it had been for millions of years. Net effect, more carbon in the atmosphere. The carbon in the goat methane comes from the grass, which took that carbon out of the air a few months back. Net effect, nil. I hate it when people get anxious about cow farts contributing to global warming. But the thoughts about the transportation of the goats are worth exploring. However, if you want to go that route you also have to add the net carbon emissions for construction, maintenance, and transportation of the lawnmower, which are non-trivial. I strongly suspect the goats are a net win.

Alex3917 17y ago
"The carbon in the goat methane comes from the grass, which took that carbon out of the air a few months back. Net effect, nil." Can you explain this? The grass absorbs CO2, and the goats turn the grass into methane. Except that methane is a way more potent greenhouse gas than CO2. So how could the effect be nil?
- seanc 17y ago
  Well okay, not nil. But the methane eventually oxidizes back to CO2, half life 7 years: http://en.wikipedia.org/wiki/Methane http://en.wikipedia.org/wiki/Methane. Contrast with fossil fuels, which take a looooong time to get (permanently) back into the ground.
  - gregwebs 17y ago
    From looking at the wikipedia page, methane is converted to water and ethane with broken down ozone. Ethane is a much milder greenhouse gas. Not sure what ethane half life is. If I understand this correctly, the net result will be putting carbon and hydrogen into the atmosphere (via ethane) and taking oxygen out of the atmosphere in the form of water and maybe reducing atmospheric ozone. With a side effect of 7 years of methane. Regardless, this is not a closed carbon loop, and it results in global warming.
    - jules 17y ago
      The carbon will be used by the plants to regrow where the goats grazed. Goats turn grass into stuff and the grass will turn it back into grass. Net effect: zero. The difference with mowers is that they turn fossil fuels and grass into mowed grass. Other organisms will turn the mowed grass into stuff (like the goats) and grass will turn this back into grass. Net effect: burned fossil fuels.
    - lutorm 17y ago
      It is a closed carbon loop as long as the grass the goats turn into methane ultimately regrows. It's true that you have a sustained amount of methane due to the flux through this loop. The same is true for fossil fuels, in principle the loop is closed because eventually plants will turn the CO2 back into fossil fuels. It's just that because the time constant of that loop is thousands of years and we burn it much faster than that, most of the fossil carbon will eventually make it into the atmosphere. Even though methane is a more efficient greenhouse gas than CO2, the time constant on the CO2 cycle more than makes up for that difference. When making these calculations, you can't just look at the amount of emission, you need to look at what sustained amount of atmospheric level results from that emission.
- ggrot 17y ago
  It also depends somewhat on what you do with the grass from the lawnmower. If you just throw it on a landfill, as it decomposes, it too will release methane. This is why many (although not nearly enough) landfills have small methane-burning power plants next to them.
TheSOB88 17y ago
The problem with methane is that it's more efficient at keeping heat in than carbon dioxide is. So while the net carbon effect may be nil, the carbon is producing more trouble because of the cows.

by seanc 17y ago

Alex3917 17y ago

"The carbon in the goat methane comes from the grass, which took that carbon out of the air a few months back. Net effect, nil." Can you explain this? The grass absorbs CO2, and the goats turn the grass into methane. Except that methane is a way more potent greenhouse gas than CO2. So how could the effect be nil?

seanc 17y ago
Well okay, not nil. But the methane eventually oxidizes back to CO2, half life 7 years: http://en.wikipedia.org/wiki/Methane http://en.wikipedia.org/wiki/Methane. Contrast with fossil fuels, which take a looooong time to get (permanently) back into the ground.
- gregwebs 17y ago
  From looking at the wikipedia page, methane is converted to water and ethane with broken down ozone. Ethane is a much milder greenhouse gas. Not sure what ethane half life is. If I understand this correctly, the net result will be putting carbon and hydrogen into the atmosphere (via ethane) and taking oxygen out of the atmosphere in the form of water and maybe reducing atmospheric ozone. With a side effect of 7 years of methane. Regardless, this is not a closed carbon loop, and it results in global warming.
  - jules 17y ago
    The carbon will be used by the plants to regrow where the goats grazed. Goats turn grass into stuff and the grass will turn it back into grass. Net effect: zero. The difference with mowers is that they turn fossil fuels and grass into mowed grass. Other organisms will turn the mowed grass into stuff (like the goats) and grass will turn this back into grass. Net effect: burned fossil fuels.
  - lutorm 17y ago
    It is a closed carbon loop as long as the grass the goats turn into methane ultimately regrows. It's true that you have a sustained amount of methane due to the flux through this loop. The same is true for fossil fuels, in principle the loop is closed because eventually plants will turn the CO2 back into fossil fuels. It's just that because the time constant of that loop is thousands of years and we burn it much faster than that, most of the fossil carbon will eventually make it into the atmosphere. Even though methane is a more efficient greenhouse gas than CO2, the time constant on the CO2 cycle more than makes up for that difference. When making these calculations, you can't just look at the amount of emission, you need to look at what sustained amount of atmospheric level results from that emission.
ggrot 17y ago
It also depends somewhat on what you do with the grass from the lawnmower. If you just throw it on a landfill, as it decomposes, it too will release methane. This is why many (although not nearly enough) landfills have small methane-burning power plants next to them.

TheSOB88 17y ago

The problem with methane is that it's more efficient at keeping heat in than carbon dioxide is. So while the net carbon effect may be nil, the carbon is producing more trouble because of the cows.