Re: Are plants a viable option to solve global warming?

You've got the right idea: plants do indeed store carbon in their fibres, 
but when the plant dies and the materials rot away, the carbon is 
released. 

Plants that are eaten, clearly end up quite quickly in the microorganism 
food-chain. After a moderate amount of time some solids remain and part 
of this goes into the ground to feed other mircroorganisms there while 
the rest becomes gasses of various kinds (CO2 and methane - CH4, etc). In 
the long run, all carbon is returned to the atmosphere. Some of the 
carbon seeping into the ground is 'locked' into carbonate rocks such as 
limestone stallagmites - but this is not a lot.

But not all plants are vegetables or herbs - trees store carbon for a 
long time - but only while they are growing. When the tree dies its wood 
decays - but over fairly long time scales. In a jungle, there is a 
balance between the amount of carbon taken up by the leaves and the 
amount of carbon released from dead trees. In plantations trees are 
typically planted and cut and new trees planted so there is an export of 
carbon from the air to the trees and out of the plantation.

Wood that is turned into books or houses or furniture stores carbon - for 
the lifetime of the object.

By planting something green almost everywhere we could, for a while, suck 
up a lot of carbon, but as soon as the plants matured that would be the 
end of it. If in the meantime we released even more CO2, from burning 
oil, gas and carbon, things would not look any better when the plants 
reached maturity.

One other possibility is to feed the oceans on minerals needed to help 
plankton grow. The plankton form carbonate skeletons, and these skeletons 
fall to the bottom of the deep oceans. Some of the skeletons are 
dissolved in the water before the bottom is reached and thereby enters 
the carbon-cycle, but the skeletons that reach the deep sea floor will be 
locked up there for a very long time. Because of plate tectonics all rock 
is recyled through the interior of the Earth sooner or later and gasses 
released at volcanoes reenter the atmosphere - so in the really long run 
(hundreds of millions of years) that is no option either. However, at the 
moment there is not enough knowledge about what happens to the oceans 
when you fertilize them to encourage increased plankton-growth, so the 
idea is not being tried anywhere. Some experiments with unclear outcomes 
have been performed.

Some links:
 
http://www.csa.com/discoveryguides/oceangard/overview.php
 
http://www.safeclimate.net/business/images/understanding_carboncycle.jpg

http://earthobservatory.nasa.gov/Library/CarbonCycle/