Understandable Earth Science

In January 2016, Stuart Gilfillan and I (Stephanie Flude) made the long drive from Edinburgh to Beighton, Sheffield to collect some gas samples from UKCCSRC’s Pilot-Scale Advanced CO2-Capture Technology (PACT) facility. The PACT facility hosts a state of the art, pilot-scale CO2 amine-capture plant that can capture CO2 in flue gases from either a 250kW air/oxyfuel combustion plant (that can burn coal, biomass or gas) or one of the two 330kW gas turbines also hosted at the facility.

The PACT Core Facility entrance and the amine capture absorber and desorber columns.

As we are Earth Scientists, rather than Engineers, we are researching reliable means to trace the fate of CO2 once it has been injected below ground for geological storage. As part of that research we are investigating how the captured CO2 itself can be used as a geochemical tracer. This means I have spent much of the last couple of years tracking down sources of man-made CO2 to sample, and swapping my usual field gear – walking boots, waterproof coat and rock hammer – for steel toe capped shoes, hi-vis jackets, torque wrenches and high pressure hosing. We wanted to collect as many different types of CO2 as possible – from different capture techniques and from different feedstocks, and so collecting samples from PACT was an obvious option.

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Our typical gas sampling equipment – no rock hammers here!

We had arranged to visit while both biomass and natural gas were being air-combusted in the 250 kW plant, allowing us to collect samples derived from two different fuel stocks. We were also hoping to collect gas samples from different parts of the carbon capture system, so we could better understand, and ultimately predict, what controls the inherent fingerprint of captured CO2. For this, we wanted to collect samples of the fuel, the combustion flue gas, the residual gas from the amine absorber column, and the final captured CO2:

pact-schem

Schematic of our ideal gas sampling strategy.

The staff at PACT were very keen to help us collect this range of samples, but early discussions raised some problems with how to collect the samples. The PACT facility had been designed incredibly efficiently, with multiple gas analysis instruments housed on site that directly tap and analyse the gas of interest. Unfortunately for us, this efficient design meant that very few external sampling ports were installed on the system – why add sample ports when you can simply flow the gas you want straight to your analyser? After discussions with Kris Milkowski and Martin Murphy, we settled on the idea of collecting samples from the exhaust vent of PACT’s FTIR system, with some supplementary samples collected straight from an external tap on a combustion flue gas pipe.

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Stuart collecting a sample of combustion flue gas from the flue pipe

Once on site, we spent a few minutes working out the best way to connect our sampling equipment (copper tubes, clamps, and gas-sample bags) to the available ports and how to ensure a strong enough flow of gas to sample. We collected from the flue pipe first and then moved across to the FTIR hut. Sampling here was a little more hectic as we had a 4 minute window to collect the sample while the FTIR was purging the gas of interest. We need to be very careful to avoid air contamination in our samples, and standard procedure for this is to purge our equipment with the gas we are collecting for at least two minutes, leaving just two minutes to collect the sample and hook up the sampling assembly for the next sample.

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Stuart explaining our sampling procedure to Kris in the FTIR hut.

By the end of the visit, we had managed to collect combustion flue gas, absorber outlet, and captured CO2 from both gas and biomass feedstocks. With the critical sampling tasks out of the way, we were treated to a tour of the combustion rig by János Szuhánszki.

Janos introducing Steph and Stuart to the combustion rig.

So what happens next? We have spent the last year analysing the samples for their inherent geochemical and isotopic fingerprint.  We have measured the carbon and oxygen isotope composition (δ13C and δ18O) of the captured CO2, and concentrations and isotope ratios of trace noble gases (helium, neon, argon, krypton and xenon) that are present in the captured CO2 stream. The results have just been submitted in a manuscript to the International Journal of Greenhouse Gas Control, so keep an eye open for that in the near future.

A version of this article also appears on the UKCCSRC Blog site.

Welcome to Part 3 of my blog sharing some of my Indonesian fieldwork experiences as part of the Soa Basin Project. My previous post described life on the archaeological excavations in the Soa Basin, but a lot of the work I did was spent further afield, hunting down layers of volcanic deposits that could be used to correlate between different excavation sites. Most of the time, I was working with my colleague Ruly, a geologist at Badan Geologi (The Geological Agency of Indonesia) and University of Wollongong PhD student, who appears in many of the photos below. This blog entry describes some of the fieldwork conditions; I’ll cover more about the geology and volcanoes of the area in a later blog post.

Out in the field, it was hot. So hot that I started strapping bottles of water to the outside of my bag and by lunchtime it was warm enough to make a decent cup of coffee with. One of the first rules of working in the tropics is to seek out shade wherever possible. You know the way a cat will find and sit in the patch of sunlight coming through a window? In the field, we do the opposite. That wasn’t always possible, and we would sometimes have to collect pumice samples from white cliffs of volcanic tephra in direct sunshine. Needless to say, it was hot and sweaty work! But it turns out that volcanic dust makes an excellent sunscreen – I never got sunburnt on sampling days.

Lunch in the field was usually similar to dinner – sandwiches aren’t really a thing in Indonesia, so we would pick up a bag of rice and baked fish and / or chicken in the morning to take with us. On particularly hot days the food would be hot by lunchtime, as though it had only just been cooked within the last half an hour  (thankfully and surprisingly, we didn’t get food poisoning).

There were two main types of field terrain in my field area. The centre of the Soa Basin is generally flat, but with deeply incised river canyons; a lot of vegetation had been cleared in the past for farming and cattle grazing, giving a dry, scrubby grassland that is easy to navigate. The edge of the basin is host to many volcanoes – some of which have erupted historically and some of which are probably extinct. Much of the area around these volcanoes is densely vegetated jungle, probably because the volcano flanks are so steep they aren’t worth clearing for agriculture.

01c SoaVolcanoes

Google Terrain map showing the volcanoes surrounding  the Soa Basin

During my first field season, we thought it would be a good idea to explore the surrounding volcanoes to collect samples and start building up a geochemical database of local volcanism. Most of these volcanoes are steep sided and covered in tropical rainforest or tall grass and a lot of the time was spent hunting for rock exposures (sometimes without success). I didn’t have my own machete (not the easiest thing to take on a plane…) and so Ruly did most of the Bushwhacking; seeing his back disappearing into the jungle became a very familiar sight.

The grass on many volcano flanks was deceptive. From a relatively close distance, it looked short and easy to walk through and there were many times when we aimed for this kind of terrain (like the hill in the background above-left), thinking it would be easy walking. But when you get closer, the grass turns out to be 1-2 m high and even harder to walk through than the jungle-vegetation.

One day, we spent over 2 hours fighting our way through just 400 m of this grass to reach some rocks exposed at the top of a small satellite cone on the flanks of Keli Lambo. (Annoyingly, we then had to make the same journey back again, but this time laden with rock samples). Another day, we were lucky enough to find an irrigation channel running through the jungle inside Welas Caldera, that we were able to walk along the top of, with minimal bushwhacking. We managed to not fall into the channel, but unfortunately didn’t find any rock exposures to investigate.

Often the best exposures were in river channels and these sometimes contained spectacular dried up waterfalls. I was itching to get a closer look at the stratigraphy exposed in these cliffs, and sometimes we were able to safely find our way to the base of the exposure, but often they were too steep to access without rock climbing equipment. Sometimes, the jungle in these dried up river canyons was so dense that we struggle to get a GPS reading once we had managed to find some rock exposures to sample.

Other times, rocks were exposed in rivers that hadn’t dried up, and these often gave us some fun close encounters with the local “wildlife”.

Away from the rivers, wildlife encounters were still common, especially with arthropods. I learnt early on to be very careful when handling interesting looking rocks, after finding a scorpion on the underside of a rock I had picked up to look at more closely (I probably should have already realised this, after finding a scorpion in my bed).

Then there were the spiders! Apart from the Huntsmen that hung around one of the houses we stayed in, I didn’t see many spiders on Flores. But the ones I did see were impressive. I have seen the stripy orb-weaver spiders before and *almost* find them more beautiful than I find them scary. I saw a couple of these hanging on webs in dried grass, usually next to a path.

The only other spiders I saw in the field were so terrifyingly big, they stopped me from sampling a lava flow exposed in a stream cutting. We were looking for rock exposures to sample on Ambulobo and spotted an exposed lava in a dry waterfall behind a bridge. We spotted a route down from the road to the river bed, but there was a massive spider web hanging over the gap in vegetation that would be the river in the wet season. On this web were three absolutely massive spiders – each had a leg span of about 20 cm (take a ruler, look at how big 20 cm, and then imagine the above photo as that size!). They were black and red and looked evil (although I have since been told that that they are just harmless orbweavers). I decided that we could probably manage without that lava sample. Ruly was much braver than me!

Other encounters included a creature that built itself a cage before turning into a chrysalis, and giant grasshoppers.

Most of the time it was just me and Ruly in the field along with our driver (one of the local people who owned a 4WD truck and hired it out to the Soa Basin project). But we often met people while in the field, even in the middle of the jungle. It wasn’t uncommon to find a family farm, or even a small traditional village. Most of the time people were friendly and helpful and we sometimes hired them for a few hours to show us the way to rock exposures. One family fed us cups of tea and deep fried peanuts while we were waiting for our driver to pick us up, and the mother gave me a beautiful tobacco bag that she had made. Another time, while we were examining an exposure fairly close to a road, a truck full of people spotted us, stopped and then insisted we take their photo(?).

Overall, the fieldwork was hard work, under quite difficult conditions. But the friendly people we met in the field, combined with the consistently stunning landscapes of the area made the work enjoyable (even when I spent all day becoming increasingly covered in volcanic ash whilst sampling).

 

 

Welcome to Part 2 of my blog where I share some of my experiences of carrying out fieldwork in Indonesia as part of the So’a Basin Project . For this post, I am going to focus on the archaeological sites because I know that the workings of a large archaeological dig are a bit of a mystery to most people. To be fair, they are still a bit of a mystery to me – I was there mostly to take geological samples and to help constrain the stratigraphy of the area – but just being on the site, listening to the (very loud) chink of hammers and seeing a stegodon tusk slowly revealing itself a little more everyday was just fascinating.

The So’a Basin Project has various excavation sites scattered across the area, and thanks to the lack of vegetation, some of these show up really well on Google Earth.

Excavations from up high

Google Earth images of some of the excavations in the So’a Basin

The biggest of these excavations is a site called Mata Menge (the middle arrow on the above diagram), and it was near here that the So’a Basin team recently found hominid fossils. The site is a series of trenches, covered with tarpaulin to keep the sun (and very occasional rain shower) off both the workers and the trenches. These were very necessary as temperatures could easily reach 40 °C during the day.

As well as all of the archaeologists, geologists and other scientists visiting the site, the Project hired many people from the surrounding villages to help with the excavation. Each active trench had an experienced archaeologist as a manager, and a number of workers who had been trained to carefully excavate the sediment and rock in the trench, and identify whether a feature was archaeologically interesting (e.g. an artifact, fossil, or change in stratigraphy) and report it to the trench manager, who would note its location and investigate it further.

There were often dozens of people simultaneously using hammers and chisels to excavate the trenches; the first few times you hear this sound it is quite amazing, but it soon develops into a kind of musical background rhythm, that you only notice most when it stops as soon as the whistle blows for lunch break.

At the end of the day, the location of all of the finds (artifacts and fossils) needed to be measured and logged. This was a two-person job with one person taking a levelling rod to each find-location and placing it above each find, and another person manning the Total Station (a combined theodolite and EDM – electronic distance measurement) to measure (very precisely) the location of the find. This could easily add an extra 2-3 hours onto the end of the day if there were lots of finds that day.

Being very pale-skinned and a red-head (albeit out of a bottle), I am used to my appearance drawing a lot of attention when I visit hotter climates. This was exacerbated on my first trip to Mata Menge as I arrived near the end of the season, so was also the unusual newcomer. I lost count of the times I would be taking a sample from the wall of a trench and look up to realise that I had attracted an audience. Sometimes they were wondering if I needed any help, but other times they just wanted to watch whatever I was doing.

The trenches themselves were fairly free of local wildlife, but the wider area was grazed by local cattle and horses, and it wasn’t unusual to encounter a herd of buffalo or other exotic cattle while walking between sites.

Another site, about a 15 minute walk from Mata Menge, is Wolo Sege. It was here that Adam Brumm et. al. found some stone artefacts right below an ignimbrite deposit that was dated to ~ 1 million years ago. As a British, wannabe volcanologist, I was especially interested in this Wolo Sege Ignimbrite, because I don’t often get chance to look at ignimbrites that are younger than 450 million years old. It has everything a volcanologist could want – ash, pumice, accretionary lapilli and crystals (and when I say crystals, I mean shiny, 1 cm amphibole crystals – quite impressive!). The entire unit is about 3 m thick at Wolo Sege (the thickness varies where it has been identified at different sites across the region), and the top 2 m of that is ash (only the bottom part is shown on the photo below). There is a lot of ash mixed in with the pumice, and that, along with all the accretionary lapilli, suggests that there was a lot of water involved in this eruption – whether it was because of a rain storm, or erupting through a lake, we don’t yet know, though.

Wolo Sege Ignimbrite

Photo of the type-section of the Wolo Sege Ignimbrite, referenced to my stratigraphic log, and a close up of accretionary lapilli in the upper ash unit. Can you spot the accretionary lapilli clast in the ash below the pumice?

At the end of the excavation season, the trenches need to be protected to stop any partially-excavated, or as-yet-unexcavated finds being damaged by exposure. Exposed fossils are sealed in a protective gypsum plaster cast, after which plastic sheeting is laid at the base of the trench, and then all the material that has been dug out is used to fill the trenches back in again. This protects and preserves the site ready for the next season, while making it relatively easy to identify how far down you had excavated the year before.

So, that is life on an Indonesian excavation. However, I spent most of my time away from the excavation sites exploring the surrounding countryside, trying to correlate volcanic units, and I will tell you more about that in the next blog.

Mata Menge

Overview panorama of Mata Menge.

Between 2011 and 2014 I was working at the Quaternary Dating Laboratory in Denmark. For part of my work there, I was involved with the So’a Basin Project, headed by the University of Wollongong, Australia. Some exciting new finds from the project have just been published in Nature along with their age and stratigraphic context and so I thought I would share some of my fieldwork experiences from my time working on the project.

The So’a Basin is in the middle of the Indonesian island of Flores, 75 km east of Liang Bua – “The Hobbit” (a.k.a. Homo floresiensis) cave. The basin contains sediments up to ~ 1 million years old, and has long been known to contain some interesting vertebrate fossils, such as stegodons (ancient elephants), and Palaeolithic stone tools. This makes it an ideal location to try and find fossils of the ancestors of “The Hobbit” (spoiler alert if you haven’t been to read the Nature paper yet – they found some! Sadly, the fossils were found after changed jobs, so I missed all the excitement, but I’m still really pleased that I was able to contribute to this exciting work.)

Basecamp for the Soa Basin Project was in a small village called Mengeruda, where the project rented a couple of houses to accommodate the visiting scientists. Mengeruda was only connected to a (relatively) stable electricity supply a couple of years before my first visit, so the accommodation was fairly basic. One of the houses had the luxury of flushing toilets and running cold-water but if you were staying in the second house and needed the facilities in the middle of the night, you had to treck to a small shed across the yard.

Needless to say, there was no air conditioning, other than leaving the shutters open at night. However, this natural air conditioning system meant that we shared the house with a whole host of creatures. One of the first things I was told on arrival was to always check my shoes for scorpions before putting them on. I didn’t find any nasty beasties in my shoes, but I did find a scorpion in my bed on the first day (many thanks to the ladies who managed the house for pulverising that with a broom for me!). A couple of Huntsman spiders were free roaming in the house, which took a bit of getting used to. While my Australian colleagues assured me that they don’t bite, I am a bit of an arachnophobe, and getting to sleep the first few nights wasn’t the easiest. The best night’s sleep I had, however, was the night the giant gecko hung out in my room. I love geckos anyway, but this one was about 30 cm long; apart from being absolutely beautiful, I knew it would probably eat any spiders or scorpions that came in the room :-).

On my second trip, I managed to avoid close encounters with scorpions and spiders in the house, but did have to get help evicting a giant hornet that started trying to become my roommate (many thanks to Gert for his efficient wielding of a Marie Claire Magazine to evict it). Evenings were often spent sitting on the porch, writing up field notes, where the lights attracted everything from moths to a praying mantis. Unsurprisingly, there are no street lights in Mengeruda, so at night, away from the house, the only light was from stars or the moon. This meant some great views of the stars on moonless nights. Somehow, the local people were able to walk around in the dark without using a torch on  nights like this – I still haven’t figured out how!

Days in Mengeruda started early; even if you were able to sleep past the dawn chorus of birds, dogs and farmyard animals that began around 5:30, it was rare that it was cool enough to sleep past about 6:30.

A truck left Mengeruda, driving to the main excavation around 6:30 every morning. The journey on the truck took ~ 25 minutes, or it was a 45 minute walk with 2-3 stream crossings. The truck would start off fairly full with the just the Project team, but the excavation hired many people from Mengeruda and the surrounding villages, and some of them them would jump on the truck as it passed through the village, so it was often overflowing by the time it arrived at the excavation site. At the end of the day, the truck was often full of fossils, to be studied at the basecamp and later transferred to the Indonesian Geological Survey in Bandung, leaving less room for passengers, so most people walked home.

The track between the village and the excavation presented some amazing scenery. There are hot springs at the end of the village that are used by the local people as a bath (a great way to relax when a cold shower just isn’t enough to scrub off the many layers of volcanic ash, sweat and suncream that can build up during a day of sampling); early in the morning, before the air heats up too much, these produce lots of dramatic steam.

After the springs, the track climbs a hill and then offers wonderful views across rice paddies and rainforest filled valleys towards Ambulobo Volcano; this is even more dramatic early in the day, before the sun burns off the morning mists rising up from the valley. Ambulobo is an immensely pretty volcano, of which I took far too many photos – expect to see more of them in future posts 😉

Ambulobo

Spectacular view looking across the valley to Ambulobo volcano, during the morning commute to the excavation.

One of the things that first attracted me to geology, back when I was a teenager, is that is can be so pretty!

While I don’t consider myself a high-level photographer (I definitely need to upgrade my camera if I am going to do that*), ever since I got my first digital camera I have tried, with varying degrees of success, to capture the beauty of the geological world in photographs.

A couple of years ago, I submitted some of my photos to the EGU (European Geosciences Union) photo competition and was really pleased when two of them were selected as finalists.

You can see the photos in the Imaggeo database here here (Colourful Hydrovolcanism) and here (Climate Change Is In Our Hands).

In 2015, Colourful Hydrovolcanism was picked to feature as an Imaggeo on Mondays photoblog. This photoblog is published every monday and showcases some beautiful geoscience photos, with some kind of scientific explanation of the photo subject. So if you want to learn what makes the volcanic deposits at El Golfo so colourful and pretty, check out the blog post here.

Being picked as a photo-finalist and to feature on Imaggeo on Mondays was a great honour for me, and so I was even more pleased when I logged onto Twitter the other day, after the Christmas break, to find that Colourful Hydrovolcanism had also been picked as one of the best Imaggeo photos of 2015 (my personal favourite on this page is the image of the glacier collapsing – wow!). What a great start to the New Year!

Happy New Year everybody!

* Warning: camera rant. In 2006 I picked up a Canon Powershot A650; a pocket sized “point and shoot” but with a rotatable viewscreen and a decent amount of manual control over shutter speed, aperture size and “film speed”. It was a fantastic little camera. A couple of years ago a friend saw me taking photos and commented “the photos you post online – you took them with *THAT*?!!?!”. Last year (2015) my poor little camera really started to struggle. I had abused it over the years, letting it get rained on, carried in the same bag as rock samples, covered in volcanic ash; the lens was substantially scratched and the light sensitivity was definitely not what it used to be. So I decided to buy a new one. Except Canon don’t make this range any more. I eventually managed to track down a second hand version a couple of years younger than mine, in good condition, but this is also now struggling in moderate to low lighting, even on the maximum ISO of 800. I’m really hoping Canon relaunch this model because it is awesome. I don’t want a big bridge camera – I want something that will fit in my pocket or handbag, but that lets me have manual control, and has a moveable viewscreen so that I can shoot interesting angles. If anyone comes across a camera that is similar to the old Powershot A650 series, please let me know!

I’ve noticed that there seems to be a lot of anti-CCS views being aired on Twitter at the moment, along with some CCS news articles that are factually incorrect (see bottom of this post).

So here is a quick overview of what CCS is and isn’t. I intend to write more detailed blogs discussing these points sometime soon – just need to find the time.

So, what is CCS?

  • CCS stands for carbon capture and storage
  • CO₂ is captured from energy production and industry. That CO₂ would otherwise end up in the atmosphere and cause global warming.
  • The captured CO₂ is permanently* stored deep (2-3 km) underground in pore spaces in the rock.
  • CCS is the only feasible way of reducing CO₂ emissions from industry – especially the steel industry, necessary for building wind turbines!
  • CCS is a way to reduce CO₂ emissions while we are transitioning from a fossil-fuel to low-carbon energy infrastructure.
  • CCS is a fully developed and tested technology.
  • CCS is a potential way of getting negative CO₂ emissions – i.e. reducing CO₂ in the atmosphere by combining CCS with burning of biofuels for energy.
  • Implementing CCS is cheaper than dealing with the consequences of global warming.

* CO₂ will be stored deep in rocks on the timescale of thousands to millions of years. So technically not “permanently” on a geological timescale, but permanent on a human timescale and easily long enough to buffer global warming.

Now to address some of the misconceptions about CCS.

What CCS is NOT:

  • CCS is NOT an excuse to keep burning fossil fuels indefinitely.
    • CCS can minimise CO₂ emissions while we transition from a fossil-fuel to a low-carbon energy infrastructure over the next 50-100 years. I do not know anybody working with CCS that thinks it is a long term solution that will let us keep burning fossil fuels.
  • CCS is NOT unnecessary for reducing our CO₂ emissions.
    • Many reports (including IPCC) show CCS is needed to meet climate targets.
    • Existing energy infrastructure cannot yet cope with the intermittency of many forms of renewable energy.
    • CCS is currently the only way to reduce industry CO₂ emissions.
  • CCS is NOT storing CO₂ in caves / fractures.
    • In the vast majority of storage sites, CO₂ is and will be stored in rock pore spaces many kilometres underground. Up to 20% of the volume of a rock can be empty space – think of a box of marbles and the gaps between the marbles. That is where the CO₂ will sit. And the storage rocks are deep, with many impermeably layers on top of them which means the CO₂ will not leak out of the ground.
  • CCS is NOT a new, un-tested technology.
    • Lots of CCS pilot-projects exist that show CO₂ can be captured at large scale from power plants, and the world’s first CCS power station –Boundary Dam – was opened in Canada last year (2014).
    • The storage technology behind CCS has been used for years in the oil industry for something called enhanced oil recovery (EOR) where CO₂ is pumped into an oil field to get more oil out of the ground, and there are lots of storage pilot projects that show that the CO₂ can be injected into deep rocks, without causing earthquakes and without leaking.

What CCS is and is not

So, onto the newspapers that are getting their facts wrong.

On January 6th 2015, The Guardian published this article, including the following paragraph:

“CCS is strongly supported by energy companies like Shell. It involves the sequestration and piping of carbon dioxide into underground fissures and currently aids fossil fuel extraction, as well as allowing their continued burning long into the 21st century.”

Carbon dioxide is NOT pumped into underground fissures! It is injected into pore space in rocks!

Then we have this pleasantly optimistic article in the Irish Times published on January 8th 2015 that contains 2 slip-ups I feel need correcting.

Firstly is this paragraph with similar problems to the Guardian article:

 “Statoil has been trying out CCS at its Sleipner natural gas field in the North Sea since 1996. Since then, it has injected some 14 million tons of carbon dioxide into geological caverns and “successfully” proved that it is technically feasible, the company’s Olav Skalmerås said in Bonn.”

There are no caverns in the Sleipner natural gas field. The CO₂ stored in Sleipner (and the natural gas that has been stored in the rocks at Sleipner for thousands to millions of years) exists in the pore spaces between grains in the rock. For more information, see this article by the British Geological Survey.

Next was this paragraph:

“Novel approaches to carbon capture are also being tested. One €8.75 million project in Iceland called CarbFix, which has EU support, involves capturing carbon dioxide from a power station, dissolving it in water and effectively “mineralising” it as basalt for injection into volcanic fields.”

This is a different kind of technology from most CCS storage projects; here the CO₂ is stored by reacting it to make a solid mineral. Maybe I am nit-picking, but “effectively “mineralising” it as a basalt” is incorrect. Basalt is not a mineral – it is a rock (a volcanic rock that forms from lava flows, like the current Bárðabunga / Holohraun / Nornahraun eruption). In this project, basalt is the storage rock that the CO₂ is being injected into. The CO₂ reacts with calcium in the basalt to produce a carbonate mineral called calcite, which should be stable for thousands to millions of years. For more information, see the CarbFix website.

In my first climate-related blog I talked about why I was so angry that the world wasn’t taking action to prevent climate change – 10 years ago the wedges concept, introduced  by Pacala and Socolow [1], gave a clear prediction of how our annual CO₂ emissions were increasing and identified ways to reduce emissions. Back then, the world was still thinking in terms of how CO₂ *emission rates* affect climate change. Since then we have realised that emission rates are relatively unimportant and that global cumulative CO₂ emissions are what we need to keep an eye on.

This is because CO₂ has a long residence time in the atmosphere – if we were to completely stop burning fossil fuels and emitting CO₂ today, it would take up to 35 thousand years for all of the CO₂ we emitted since the industrial revolution to be re-absorbed [2] (if you want to know more about that, there is a nice blog here). This means that our CO₂ emissions over decades, even centuries, are pretty much instantaneous on the carbon-cycle timescale.

CO₂ residence

Figure 1: Carbon is stored as fossil fuels for millions of years. When we take it out of the ground and burn it, we are releasing CO₂ instantaneously on geological timescales. It then takes tens of thousands of years for that CO₂ to be removed from the atmosphere and be stored long-term in the Earth.

The amount of global warming will be controlled by the amount of CO₂ hanging around in the atmosphere, and, because it hangs around in the atmosphere for so long, that is controlled by the total amount of CO₂ we have emitted, rather than how fast we are emitting it. In 2009, Allen et al [3] calculated the Earth will warm by ~2 °C for every 3.67 trillion tonnes of CO2 that we emit [4]. If we want a good chance of avoiding global temperature rise of more than 2 °C, the most CO2 we can emit is 3.67 trillion tonnes – total! period! ever!.

Reducing emission rates just delays the 2 °C temperature rise – it doesn’t prevent it. Stabilising emission rates buys us time but doesn’t solve the problem. The only way to solve the problem is to completely stop emitting CO₂.

This next diagram, simplified  from the IPCC 2014 report (Figure SPM.5, p9 [5]), is a nice illustration of  how much we can expect the global temperature to rise because of the total amount of CO₂ we emit. The x-axis shows cumulative CO₂ emissions since 1870 in gigatonnes of CO₂. (GtCO₂) The y-axis shows the temperature increase compared to pre-industrial temperatures. There are different ways of modelling the climate response to carbon dioxide emissions, and that is why this graph is plotted as a grey band, rather than a single line – the band represents the range of expected global warming according to lots of different models and calculations. Those different models and calculations all agree pretty well.

Expected warming from CO₂ emissions

Figure 2. Global warming due to total CO₂ emissions with observed data and future predictions for different mitigation strategies

According the graph, when we have emitted 3670 Gt CO₂ (3.67 trillion tonnes), we can expect the global temperature to have risen between ~1.4 and ~3.1 °C (black dotted line shows 3.67 trillion tonnes vs 2 ܄C).

The black ellipse labelled “Observed” plots our actual total CO₂ emissions between 1870 and 2005 against the observed warming (as an average of the years 2000 to 2009 compared to an average of the years 1861 to 1880). As you can see, it fits the predicted warming very well.

The red line shows the cumulative total CO₂ emitted as of today [4], December 23rd 2014 (2150 Gt CO₂) and that, no matter what happens, we are already committed to global warming of between 0.8 and 1.8 °C.

The other ellipses are predictions for the amount of CO₂ we will have emitted in the year 2100 for different CO₂ mitigation strategies, and the amount of global warming we would expect. Figure 3, below, is simplified from Figure SPM5 of the IPCC 2014 report and shows the corresponding CO₂ emission scenarios. The blue scenario (blue ellipse in Figure 2, blue band in Figure 3) represents the likely outcome if we use an aggressive strategy to cut CO₂ emissions and are actually able to completely stop emitting CO₂ and start creating negative emissions – actively taking CO₂ out of the atmosphere faster than nature. The yellow scenario represents a CO₂ reduction strategy that sees us managing to stabilise global CO₂ emission rates at their current levels (i.e. the emission rate doesn’t increase) and then decrease emission rates in about 30 years time. In this scenario, we would still be releasing around 50 Gt CO₂ every year, to start with, and that means we would have spent our CO₂ budget within about 30 years; by 2100 we would have emitted 4-5 trillion tonnes of CO₂ and would see global warming of 2.5 to 3 °C. The orange scenario shows what would happen if we slow the increase in emission rate and stabilise CO₂ emissions in about 3 years time – by 2100 we would have emitted ~ 6 trillion tonnes of CO₂ and would see global temperature rises of 3 – 4 °C. The red scenario represents “business as usual” – what we would expect to happen if we didn’t make any special effort to reduce CO₂ emissions. In this scenario, emission rates would continue to increase over time and we are looking at > 6.5 trillion tonnes of CO₂ emitted with temperature rises of > 4 °C by the year 2100.

Predicted CO₂ emissions

Figure 3: Predicted annual CO₂ emissions over time for different mitigation strategies

In summary, if we want a good chance at avoiding a 2 °C global temperature rise, then we can’t emit more than 3.67 trillion tonnes of CO₂. We have already emitted more than half of that in just the last 145 years. Our global CO₂ emission rates are continuing to rise and if we don’t take action quickly, we will have reached that limit within 30 years.

Notes and references:

[1]  Pacala, S. & Socolow, R. Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies. Science 305, 968–972 (2004).

[2]  Archer, D. Fate of fossil fuel CO₂ in geologic time. Journal of Geophysical Research 110, (2005)

[3] Allen, M. R. et al. Warming caused by cumulative carbon emissions towards the trillionth tonne. Nature 458, 1163–1166 (2009).

[4] Reference [3] talks about “the trillionth tonne” – why are you talking about a budget of 3.67 trillion tonnes?

CO₂ emissions can be described in terms of mass of CO₂, or mass of C (i.e. the mass of carbon in carbon dioxide): The element carbon has an atomic mass of 12 and oxygen has an atomic mass of 16. So carbon dioxide has a molecular mass of 44, which is 3.67 times greater than the mass of carbon. Allen’s paper [3] and the website http://trillionthtonne.org/ both discuss CO₂ emissions in terms of mass of carbon – emitting 1 trillion tonnes of carbon (as carbon dioxide) will produce 2 °C warming. To convert this to mass of CO₂ we just multiply by 3.67. The graphs I used in this blog post used emissions and emission rates for CO₂ rather than just C, so I used CO₂ emissions and emission rates to make things simpler. The 2150 Gt CO₂ I quoted as having been released between 1870 and today was calculated by looking up the real-time cumulative total C-emissions from http://trillionthtonne.org/ (586 Gt) and multiplying it by 3.67.

[5] http://ipcc.ch/pdf/assessment-report/ar5/syr/SYR_AR5_LONGERREPORT.pdf