SR15 and BECCS

Bio-Energy Carbon Capture & Storage

I've been reading a lot about climate change recently.  I'd like to help move this issue further up the political and news agenda, but the problem is that any claim can easily be dismissed as coming from a fringe source and countered with a claim from another source.  So it really helps that the IPCC exists and makes regular reports to the UN.  No one can dismiss the IPCC as "fringe".  Many scientists believe they take a too conservative line for political reasons.  But this too is quite handy as it means that when the IPCC say "we need to do at least this", then everyone(*) agrees we need to do at least that.

I've been reading the IPCC's Special Report: Global Warming of 1.5 ºC Summary for Policymakers.  The UN asked the IPCC to report on the differences between a +1.5ºC future and a +2ºC one, and in 2018 they did.  A lot of the report consists of bland qualitative statements along the lines of "well, 2ºC would be worse than 1.5ºC".  For example:

Risks from droughts and precipitation deficits are projected to be higher at 2°C compared to 1.5°C of global warming in some regions (medium confidence).

However, there were some strong statements and even some quantitative ones.  So, here's my summary of The Summary:

• Current warming (since pre-industrial times) is 1ºC with an uncertainty of 0.2ºC either way
• At 1.5ºC 70-90% of Coral reefs will die. At 2ºC it's 99%
• If Paris commitments are met, but nothing else is done, we're heading for 3ºC by 2100 (!)
• The IPCC could only get warming to remain below 1.5ºC by modelling scenarios in which emissions fell to zero by 2050.  Even then many models predicted an overshoot. 
• In order to stay below 1.5ºC (or overshoot and return) emissions need to start falling within the next few years.  (At the moment they are going up.)
• The remaining carbon budget for a 50:50 chance to stay below 1.5ºC is between 580 and 770 GTon.  We are emitting 42 GTon per year so, if we all we do is stop increasing our emissions, 1.5ºC will become a 50% likelihood in 14 years time, even if all human activity then ceases.
• However, they go on to say that uncertainties in climate response and non CO2 emissions reduce the budget by 400 GTon, uncertainties in the level of historic warming reduce it by 250 GTon, and uncertainties in permafrost methane release by 100 GTon.  The upshot of which is: we may have passed the point of no-return already.  This possibly explains why they go on to talk about CDR (see below).
• Every single simulation in which the 1.5ºC target was met required massive CDR schemes to start now.  (Carbon Dioxide Removal - often referred to as geo-engineering.)
• The main forms of CDR proposed are aforestation and BECCS (Bio Energy Carbon Capture and Storage - see illustration).  The feasibility of others are not yet known.
•  SRM (Sunlight Reflection Methods) were not included in any models because of ethical and management concerns and because they do not solve the problem of ocean acidification (which can itself trigger further carbon release.)

The message is pretty clear even if the language used (even in the summary for policymakers) obfuscates.  We need to start reducing our emissions now, we need to get to zero by 2050, and we need to start large scale CDR now.
I was interested by BECCS as I'd not heard the term before.  It turns out that this involves growing biomass as fast as possible, burning it, and capturing the carbon in the chimney stacks where it is far easier to extract because concentrations are so high.  The obvious downside is that the land use will compete with other land uses such as agriculture but there's an upside too - power generation.  The other feasible CDR method that the IPCC considered was aforestation, but this will consume even more land because each acre can only extract a fixed amount of carbon from the atmosphere.  Plus it has no power upside.

So let's get going with BECCS!

UPDATE 17/Jan/2020

It's possible that the tone of my original post was overly optimistic.  There are issues with scaling BECCS, or any form of CCS for that matter.  One of them is where to put the mineralized CO2.  Let's run the numbers.

• We produce 10GTon atmospheric carbon annually (or 44/12 * 10GTon CO2)
• Suppose (unrealistically) that we can mineralize all of this to stackable diamond blocks
• Diamond has a density of $3.5Ton/m^3$ giving $2.9\times10^9m^3$, or about 3 cubic km
• That would cover Staffordshire in a layer of diamond one metre thick every year
• Or Cambridge in 5 days

Of course real CCS solutions will produce a much less dense mineral, and will be made somewhat less carbon negative as a result of the mining and refining needed to produce the input chemicals.  And of course CCS does nothing to deal with the greenhouse gasses that are not carbon dioxide.  (These have the same warming effect as about half the CO2 we emit.)

The upshot is that, whilst there's no reason not to do BECCS, and it is a useful alternative energy source, we mustn't let carbon negative technologies distract us from the fact that we have to wean ourselves off fossil fuels, fast.

UPDATE 28/Jun/2020

I've completely changed my mind about BECCS now.  It's not just an issue of where to put the mineralized CO2, it's also where the bio-fuel comes from in the first place.  As this article states, the vast majority used by places like Drax at present comes from clear cutting carbon rich (and biodiverse) forests in the southern USA.  It is patently obvious that BECCS cannot possibly be carbon negative unless the fuel comes from biomass from agriculture, not deforestation.  Well, it's patently obvious to everyone except our government, who are funding the venture at Drax so that it can break even.

Then there's the fact that no-one has managed to actually get CCS working effectively.  Clearly this is no reason to stop research, but it would be a serious case of "all our eggs in one basket" to bet on CCS working in the future instead of switching to renewables, and - critically - reducing energy consumption now.

Could bio-fuels replace our energy needs, even in principle?  It has been calculated that (using unrealistically optimistic assumptions) there's space for another 1.2 trillion trees.  The average wood biomass for the fast growing eualyptus after 6 years growth is about 300kg, giving us about 50kg per tree-year or, about 60GTon of biomass globally.  However, only half of this is carbon, so that equates to about 30GTonC, and biofuel generators are only about 38% efficient, which makes this equivalent to about 11GTonC in coal form.  That is, approximately, equivalent to our annual emissions from fossil fuels, but note how ridiculously optimistic our assumptions have been, such as that all the seedlings will take and we'll be able to grow the fastest growing species of tree in absolutely every location.  We haven't even factored in the energy costs of growing and transporting the fuel, but it's worth pointing out that in most agriculture the calorific value of the produce is less than the energy used in the production and transport.  And goodness knows what this would do to food prices.

Cutting our energy demand and switching to renewables remain - by far - the most feasible ways of dealing with our emissions.  Other ideas may be worth looking into, but when they become viewed as a panacea they do much more harm than good by making us give up on the difficult course of action we have to take.

Banking on BECCS is a bit like giving up chemotherapy for homeopathy.

FOOTNOTES

(*) Well, almost everyone.
(!) Note, however, that the IPCC do not take feedback loops into consideration when making their predictions.  In the real world 3ºC will not happen without triggering large scale permafrost methane release which will push the temperature higher still, possibly triggering other feedback loops such as the methane hydrate release from the sea floor.  This is important since it only takes 6ºC warming to get us back to the conditions of the end-Permian mass extinction event.