Very little of Earth's Biomass, which has generally been around 100 gigatonnes a year in terms of carbon IIRC, ever ends up as oil/coal/etc... though odds are much more oil and nat gas was produced and lost than we have since they tend to leak and earthquakes can rupture pockets, bacteria then eats it up... our world oil supply (known reserves) is roughly equivalent in mass to annual biomass production, being generous all those various fossil fuels might be somewhere between a decade to a centuries worth of planetary biomass production... so keep scale in mind here, all those wonderful fossil fuels are a teeny tiny fraction of a percent of a percent of our planet's total production to date... there are 1,324,000,000,000 proven barrels of oil in reserves, and you get 433 kg of CO2 from burning on, or 5.73x10^14 kg... but the known amount of CO2 currently in the atmosphere is 30x10^14 kg, so torching all known oil only adds about 17% to that... keep in mind again that biomass figure (if it helps a gigatonne is about 10^12 kg, that fossil fuel CO2 was 573 GT and atmosphere CO2 3000 GT) which since CO2 is about 1/4 Carbon by mass (12/44 but close enough) so you can sequester carbon very fast if you need to.

Also, keep in mind that biomass sequesters the stuff temporarily, limestone and similar do it close to permanently and is in constant production but obviously slowly and not by any agricultural technique. Once killed a chunk of biomass begins emitting CO2 (it always does ofcourse but it generally absorbs an equal amount or more while growing) as it decays, obviously a large wooden table does this very slowly so one doesn't just have to 'dump the stuff down a hole', a ton 'sequestered carbon' in furniture format in each of a billion household for instance is a gigatonne right there, a years supply of biofuel in cisterns stored as a reserve would seriously stabilize fuel prices and the nice thing about a 'ethanol spill' is that it's as environmentally damaging as spilling a jack and coke on the lawn at a BBQ. Call it 60 billion barrels, which in case you're curious is about 10 billion cubic meters. Of course a ton of wood is hardly a lot of furniture or housing and we can turn the stuff into plastic too, or take rough lumber coat it with wax or something and dump t down a hole but as mentioned I consider the 'dump it down a hole' method intensely retarded and eye-rolling indicative of why environmentalists generally do such a wonderful job angering or scaring industrialists, who alternatively would smile cheerfully at being able to sell some immense 300 pound hardwood desk to consumers with a sticker on it saying 'extra massive for increased sturdiness... help sequester carbon and buy products that will last a life time' as opposed to paying to dump a few hundred pounds of carbon in a hole. Of course another great way to sequester carbon is to increase the amount of it stored in food, like increasing crop yields since agriculture sequesters more carbon per unit area and time than damn near everything else, especially a useless piece of desert. And if we ever start being able to mass manufacture graphene, which is now selling at a mere million bucks a square meter down from around a hundred billion a couple years ago not long after it was disvoered, we've got something else really cool to dump carbon into, since graphene and carbon anotubes are 100% carbon... there's also carbon aerogel, wonderful insulator, that we can turn the crap into that too as production spins up... ya know those wonderful space elevators I mentioned in the 'oops misunderstood you' section of the last post would weigh around 10 GT all on it's own, all 'sequestered carbon' if the feedstock to make it was air or biofuel or whatever, so don't think we can't find ways to use excess carbon besides dumping it down a big hole, and whatever it's other negative effects increased CO2 does increase plant growth and if you have some non-fossil fuel power source you can desalinize and pump with there's plenty of arid land that could 'sequester' the stuff as trees or food... corn stores up about 500 pounds of CO2 per ton itself... we presumably need to sequester about 100 tons per person... just to keep scale always foremost here, a thousand board feet of lumber weighs around 8 tons, it takes thousands of board feet to build a house, so you can use up carbon pretty quick when you need to.

But from your comments I think you misunderstand sequestering, while by and large carbon comes out of the air for plants and returns to the air from plants (by and large, limestone and the like don't appear from magic nor does all carbon in the air come from dead plant matter or fossil fuel) fundamentally carbon stored for a century is out of play. You've got Z carbon, with Z= X+Y where X is the stuff in the air and Y is the stuff stored in biomass. You want X to be a certain amount at all times, 3000 GT I guess, but Z is rising as we burn fossil fuels, so Y must go up to match it. If you are currently getting, say, 10 tons/ acre out of some crop that turns over in a year, pretty much nothing has happened, you sequester 10 tons basically, but if you use some other crop that also sequesters at 10 tons a year but doesn't have turnover of a year, but rather of a century, with presumed biomass on the spot being 1000 tons, that 1000 tons is effectively 'out of play' or sequestered continuously... that's about how much a redwood weighs by the way and you do get multiple trees per acre though I can't give you an exact mass per acre figure but they'd sequester that 600 GT of carbon dioxide on about 10^8 acres, roughly Texas size, or about a third of Libya, and one can't help but point out that fog, which is necessary to grow redwoods, is fairly easy to produce with various passive desalinization methods. Roving a bit off topic, "Neat cool magnetic algae' and heading towards my general 'why global warming worries me not so much' which I'd like to avoid but I did want to go over sequestering since I think you may be a bit unclear on the subject based on your comments. Also let me take a moment to say that all these numbers are quick Googles and/or napkin math so may be inaccurate.