seaweed, ftw?
Wired: “Group Touts Seaweed As Warming Weapon.”
The idea is simple: deforestation? No problem – just use the vast amounts of space out there in the oceans to grow a bunch of seaweed and algae of various sorts, which apparently photosynthesize carbon dioxide “at rates comparable to the mightiest rain forests.” Better: they grow quickly.
Critics say that this isn’t truly carbon sequestration if the seaweed is then fed to people, because then the carbon is released right back out. I clearly don’t know enough of the mechanics of photosynthesis – I thought the carbon was transformed and/or incorporated into more complex structures, not merely stored? And if it’s stored as something other than carbohydrates and (as the Wired article says) the carbon is released into the atmosphere as seaweed decomposes, isn’t it a good idea to feed it to people, then?
Ahha, gummint scientists to the rescue:
Q. Should we be concerned with human breathing as a source of CO2?
A. No. While people do exhale carbon dioxide (the rate is approximately 1 kg per day, and it depends strongly on the person’s activity level), this carbon dioxide includes carbon that was originally taken out of the carbon dioxide in the air by plants through photosynthesis – whether you eat the plants directly or animals that eat the plants. Thus, there is a closed loop, with no net addition to the atmosphere.
Anyway. The question of using seaweed to combat the insanely high levels of carbon dioxide humans put out is only beginning to be explored, but already it is an interesting idea!
December 10th, 2007 at 4:41 pm
Interesting idea. Recently there was a study showing that the ocean was maxing out on the amount of CO2 it was capable of absorbing, only now I can’t find the study, so I have no idea if I’m misremembering it or not….
December 13th, 2007 at 3:07 pm
If you absorb CO2 into biomass that you then feed to people or other animals, that biomass is mostly converted back into CO2. A small amount of it is retained, but that usually gets converted into CO2 once whatever it is dies.
So if you want to really sequester the carbon you would have to bury the seaweed or quickly sink it to the bottom of the ocean, where it would take hundreds of years to make it back up to the surface, if it ever did.
As to the CO2 absorption capacity of the ocean, the latest information I have seen suggests that the capacity does scale with the quantity of CO2, but it also increases the net rate of respiration so it doesn’t make much of a difference in the net CO2 level in the atmosphere.