Negative emissions

Global temperatures are rising by 0.2 degrees C every decade, on average. The plan to reach zero CO2 emissions by 2050 therefore means that temperatures will rise by at least 0.6 degrees by 2050.  I say at least because as we stop burning coal, we'll also emit less sulphur dioxide.  Sulphur dioxide aerosols help cool the earth.  The impact of the the rapid rise in Chinese and Indian CO2 emissions on global temperatures has been partially offset by the concomitant rise in SO2 emissions.  As their electricity grids switch to renewables, nuclear and gas, SO2 emissions will decline.  The cooling impact of SO2 emissions is short-lived--we know that from the effect on global temperatures of volcanic eruptions.  So reducing SO2 emissions will lead to a rapid rise of global temperatures back to where they should have been based on CO2 emissions.  This will make the observed temperatures rise faster than they have done.

And that assumes we reach zero emissions by 2050.  We might not.  Even though falling costs will drive the replacement of fossil fuels by renewables in electricity generation and transport, there will still be emissions from iron and steel, cement, air travel, agriculture and land clearance.  So analysts are looking for ways to remove CO2 from the atmosphere.  Carbon capture and storage is one way to stop the CO2 emissions of a coal power station reaching the atmosphere.  The gas is extracted from the exhaust flues of power stations and buried underground.  But there are a few flies in the ointment.  First, the gas may leak from its underground reservoirs.  Second, the process is expensive.  It adds as much as 100% to the cost of electricity generated by coal.  And all that does is stop new CO2 from entering the atmosphere.  It doesn't do anything about existing CO2.

So what we need is some process which can extract CO2 from the air and bury it permanently underground.  We do in fact have both, and I've talked about them before:

Turning CO2 to rock
Extracting CO2 from the atmosphere
Carbon capture and storage


The BBC has recently published two articles about the process of capturing CO2 from the atmosphere and turning it into rock:

Key 'step forward' in cutting cost of removing CO2 from air
Turning carbon dioxide into rock - forever

People have got quite excited by the Carbon Engineering project.  The company has managed to cut the cost of extracting CO2 from the atmosphere to $100 per tonne of CO2.  This is a lot cheaper than it was.  But it's still $100/tonne.  That's much more expensive than switching to wind and solar and EVs.  Wind and solar are cheaper than coal and gas.  EVs will soon be cheaper than petrol/diesel cars.  Since big chunks of the population, especially in America, still think that somehow switching to renewables is costly and will reduce GDP, who on earth is going to pay $100/tonne to remove CO2 from the atmosphere? 

Of course, by 2050, we may all be feeling very differently as catastrophic climate change takes hold.  And for the production of cement, we will need CCS because cement is produced by driving off the CO2 from limestone, which consists of calcite (CaCO3) and dolomite (CaMg(CO3)2).  However, that will be cheaper to do because we will be able to take the CO2 directly from the exhaust flues of the cement factories.  Right now, the Carbon Engineering project is producing synthetic liquid fuels. That means they're not actually reducing the amount of CO2 in the atmosphere, because when the fuel is burnt,  the CO2 will go straight back into the air.  However, they're preventing a rise in CO2, because for each litre of synthetic fuel burnt, a litre stays in the ground.  And apparently making the synthetic fuel moves them closer to covering their costs.

"This is a real step forward, and it's not just our company saying it," Prof David Keith from Harvard University, and a founder of Carbon Engineering told BBC News.

"I hope this changes views about this technology from being this thing which people think is a magic saviour which it isn't, or that it is absurdly expensive which it isn't, to an industrial technology that is do-able and can be developed in a useful way."

Prof Keith's "useful way" is not to simply suck carbon out of the air but to use the extracted gas as a key raw material for synthetic liquid fuel. The company is currently making around one barrel a day by combining the pure CO2 with hydrogen derived from water, using renewable energy.

"What Carbon Engineering is taking to market is first of all carbon neutral fuels, in that sense we are just another emissions-cutting technology, there is no net removal from the atmosphere," he said.

"We see our long-term fuels plant as being roughly 2,000 barrels a day, but the next one we build will be the first real commercial plant but will be 10 times smaller than that - we are developing that right now, looking for very cheap solar or wind power and looking for investors."

The firm believes that this approach to liquid fuel has major advantages over biofuels in that it uses far less land and water. Prof Keith said that if their fuel gets the same subsidies as other carbon neutral approaches then they will be able to raise funds and build plants very quickly.

[Read more here]

So, useful, but not a game changer. 

Before and after: porous basalt (left) and basalt with mineralised CO2 within its pores (Source: BBC)

Turning CO2 into rock involves dissolving the CO2 in water and pumping it into basalt rocks underground.  The acid produced by dissolving the CO2 reacts with metals (calcium, magnesium and iron) to produce rock. 

Sandra Snaebjornsdottir, a geologist working for CarbFix, has the evidence in her hands: a cylindrical sample drilled out from the site shows a smattering of chalky crystals encrusted in the basalt.

"These white bits are carbonates, or mineralised CO2", she says. "Fresh basalts are like sponges, with plenty of cavities that are filled with the CO2.

"Iceland is particularly favourable for this type of CCS simply because of the amount of basalt it's got".

Last year, 10,000 tonnes of CO2 were "digested" by CarbFix.

Yet this is tiny fraction - less than the yearly emissions of 650 Brits or 2,200 American cars.

And it becomes even more insignificant against the 30-40 gigatonnes of CO2 (a gigatonne is a billion tonnes) that modern humans pour into the atmosphere annually.

Despite its relatively small scale, experts anticipate CarbFix could be easy to repeat - thanks to the ubiquity of basalt around the world.

"Basalt is actually the most common rock type on Earth, it covers most of the oceanic floors and around 10% of the continents. Wherever there's basalt and water, this model would work", says Sandra Snaebjornsdottir.

Large basaltic areas are found in Siberia, Western India, Saudi Arabia and the Pacific Northwest.

And scientists are now looking at testing the model on the oceans to take advantage of the large areas of submarine basalt formations.

Potentially, basalt could solve all the world's CO2 problems says Sandra: "The storage capacity is such that, in theory, basalts could permanently hold the entire bulk of CO2 emissions derived from burning all fossil fuel on Earth."

[Read more here]

Two snags.  One, this costs.  In my earlier post the plant is quoted as saying $17/tonne.  And that's from using a concentrated flue gas.  If the CO2 had to be extracted from the atmosphere, then you'd have to add another $100.  Two, the process uses a lot of water. 

I'm not carping.  These are both potentially useful advancements.  As we move down the learning curve/ economies of scale the costs will fall.  However, by far the cheapest option is to slash emissions as fast as we can.  It will be much cheaper to switch to renewables than it will be to try and remove CO2 from the atmosphere after we've burnt the fossil fuels.