Current CO2 concentration in the atmosphere

It’s still the lock-in

World won’t cool without geoengineering, warns report:

According to one of its lead authors, and the latest draft [of the forthcoming IPCC AR5 report] seen by New Scientist, the report will say: “CO2-induced warming is projected to remain approximately constant for many centuries following a complete cessation of emission. A large fraction of climate change is thus irreversible on a human timescale, except if net anthropogenic CO2 emissions were strongly negative over a sustained period.”

In other words, even if all the world ran on carbon-free energy and deforestation ceased, the only way of lowering temperatures would be to devise a scheme for sucking hundreds of billions of tonnes of carbon dioxide out of the atmosphere.

As a rough guideline, 1ppm is equivalent to about 7Gt CO2. If we’re currently at 400ppm, getting down to 350ppm (a number I would suspect everyone here is familiar with), would require us to suck 350Gt CO2 from the atmosphere and sequester it. And that’s 350Gt in excess of our ongoing emissions, of course, since it has to be a net reduction.

But wait, since roughly half of our emissions wind up in the ocean — remember, that whole ocean acidification thing, a.k.a. global warming’s evil twin — as a back-of-the-envelope calculation we have to double that to 700Gt. As we draw down the atmospheric CO2 level, the ocean will give back the CO2 we forced into it, you see.

I will leave as an exercise for you, Dear Readers, how many Empire State Buildings per year (or month or day or hour) that task works out to, at 365,000 tons per ESB and whatever length of time you care to speculate it would take to accomplish that imposing task. Oh, and while you’re at it, feel free to work up some economic numbers. The usual ballpark figures I’ve seen for DAC (direct air capture) on a massive scale is somewhere around $200 per ton. Assume some technowizardry happens and we can cut that price in half. That whittles the cost to a mere $70 trillion. There’s also the question of where the heck we’d put — permanently, mind you — all that CO2. 700Gt of anything is really freaking big.

Oh, and did I mention that cutting all CO2 emissions would necessarily cut cooling aerosol emissions from burning fossil fuels? According to the copy of the AR5 report that was leaked in December, man-made aerosols have a cooling effect of nearly half of current net man-made climate forcing. That puts a very interesting spin on the question of how quickly you want to assume we could suck all that CO2 out of the air. We might find ourselves in a position of delaying fossil fuel cuts while we ramp up a DAC operation large enough to do the job, and then taper off CO2 emissions.

All of which is to say that we’ve put ourselves in a very deep and nasty hole with our past emissions. Can we get out? Of course. But anyone who tries to tell you that the situation isn’t urgent, or that it will be cheap or easy to save ourselves from almost unimaginable climate impacts, is either shockingly deluded or a liar of the first order.

2 comments to It’s still the lock-in

  • Lewis Cleverdon

    Lou – I got asked about the feasibility of Carbon Recovery in a Guardian thread a few days back – which meant keeping it short – I missed out the major biodiversity developed by native coppice and the global rural jobs benefits, but got most points covered I hope.

    In answer to your many questions I think the best I can do is to describe what we could do with biochar just from native afforestation, with the proviso that there are also large annual biomass resources produced as forestry, agricultural and non-food urban wastes.

    The prime limitation is of the land area available for native afforestation without impacting farmlands, which a recent study by WRI & WFN put at 1.6Ghas (4Bn acres) of suitable terrain. Using coppice silviculture, where small areas of native broadleaves are felled on 5 to 30yr cycles and allowed to regrow from the stump (which they do vigorously due to the large extant root ball) a global average yield of around 12Ts /ha /yr is a moderate estimate. Of this, around 50% is carbon, giving an output of 6TsC x 1.6GHas = 9.6GtsC /yr.

    From this it is clear that the most promising option for Carbon Recovery cannot offset BAU emissions – with at least a 20yr lead time to full harvest flow, anthro-output rising from the present 9.5GtsC /yr at 2%/yr would far exceed the sequestration capacity. But, given a stringent Emissions Control treaty, what that capacity can do is to advance the date and cut the level of the peak ppmv of CO2, and then gradually reduce it to the pre-industrial 280ppmv, probably at best by 2100.

    While twigs must stay in the forest to retain trace elements, the logs and trunks are hauled out but much of their weight is not the desired carbon, so minimizing transport is essential both for cost and carbon efficiency. This means that modular village-scale plants serving up to 2,000Has would be optimal, with their output from 35% efficient retorts (fuelwood to charcoal) being around 8,400TsC /yr. The process is exothermic, so besides woodgas distillation to methanol, the surplus heat output could provide some power for process and local consumption.

    That 8.4KtsC needs milling to ~2mm and charging with a few percent of compost or manure, and delivery to farmlands for interment. Fortunately the ‘Terra Preta’ areas of Brazil (covering an area equal to France and Spain, mostly in plots of ~10Has) show that the charcoal needs only to be dug in, not buried a metre deep, which implies that it can be ploughed in by farmers as part of normal cultivation. Its effects are of soil moisture regulation (moderating both drought and saturation) as well as greatly enhancing the fertility and ending annual fertilizer inputs, as well of greatly reducing soil emissions of N2O and CH4. These benefits are the reason that field trials are under way in over 25 countries, some of which show highly positive results.

    Under these assumptions the global output of biochar would be around 6.72Gts /yr, produced by around 800,000 village scale plants (river transport may justify larger plants in some places). This necessary scale would amount to a new global industry whose costs and revenues can at best only be estimated:- where the work is done by people with machetes and ox-carts production will be far cheaper than in industrialized states with raised capital outlays and labour costs.

    Beside the global market value of the methanol surplus after meeting transport needs, it is worth noting that the carbon sequestration also has value. If that is sold to corporations as offsets for continued fossil fuel use, no net sequestration occurs. OTOH, an optimal sale would be via a global platform to supply governments committed to the gradual recovery of their problematic ‘historic emissions’ in an accredited and verifiable manner, under a protocol of the requisite climate treaty.

    Assuming that CO2 could at best peak at 450ppmv in 2050, we’d then have around 170ppmv to recover, with a smaller additional volume of CO2 re-emerging from the oceans being met by biochar from other biomass wastes. At the rate of 2.1GtsC per CO2 ppmv, 6.72GtsC /yr of biochar output would clear about 3.2ppmv, and would thus take around 53 yrs after 2050 to cleanse the atmosphere, implying 2103 as the target date. As there are many factors of uncertainty, a general goal of restoring 280ppmv around 2100 seems reasonable.

    Two further points are worth noting. First, while there is no other practical prospect of avoiding the terminal acidification of the oceans, that acidification has now been shown to have two malign feedback effects in suppressing plankton: it reduces their function as a major natural carbon sink, and it cuts their output of dimethylsulphide that is a primary precursor of cloud formation, and thus of planetary albedo.

    Second, the survival of the necessary 1.6GHas of native afforestation is predictably dependent on our having stabilized the climate, which we have no practical means of achieving other than by Albedo Restoration.

    As far as I can see the establishment of stringent UN supervision of the research of the best options for both modes of Geo-E is thus pre-requisite to the resolution of the climate predicament.

    Your thoughts on added factors and questions would be much appreciated. For instance, is it too dense for most readers in this size ?



  • Lewis Cleverdon

    Regarding :”. . . a smaller additional volume of CO2 re-emerging from the oceans . . .”

    Given that around 50% of anthro-CO2 output has gone into the oceans, there are several points to consider in estimating the amount and the timing of its re-emergence due to the recovery of airborne anthro-CO2.

    - though the plankton sink has been declining, it remains a significant draw on carbon over the last 200 years which it has permanently deposited on the seabed in the remains of miniscule plankton ‘shells’;

    - the movement of both CO2 and dissolved organic carbon downwards from the surface into the deepest waters has been ongoing since the start of the industrial revolution, and while a rapid (50yr) restoration of 280 ppmv of CO2 would reverse that movement, the dynamics of ocean stratification mean that it will take as long or longer to reach the surface and be re-emitted as CO2.

    As a result of these factors, it seems reasonable to expect that ocean carbon emissions from near-surface stocks would maintain the peak airborne ppmv for some years after the recovery effort reached 3.2ppmv /yr, but thereafter the airborne concentration would decline annually towards the goal.

    But even with a raised recovery-rate due to using forestry, farm and urban wastes for additional biochar, it seems predictable that having reached 280ppmv of airborne concentration, ocean carbon would continue to be emitted, indicating the need to maintain a sequestration industry long after that goal is reached.

    In practice this need would govern the rate at which biomass resources were diverted from biochar to methanol production (which is the feedstock for a vast range of products beside liquid fuels) and/or that the coppice forests were allowed to grow out into unmanaged condition.