Despite the uncertainties, the carbon budget still requires emissions to go to zero. Without zero emissions, the cumulative emissions will keep growing and the carbon budget will be exceeded.
But how can emissions go to zero? That must mean the end of fossil fuels? Or?
If fossil fuels are combined with Carbon Capture and Storage (CCS), then it is possible to keep using fossil fuels. In an optimal situation, CCS could prevent about 90% of the fossil carbon from entering to the atmosphere. Not zero, but not too bad either.
I am sure most readers have heard of negative emissions by now. These are technologies that remove carbon dioxide from the atmosphere, such as afforestation, combining carbon-neutral Bioenergy with Carbon Capture and Storage (BECCS), or using machines to physically remove carbon dioxide from the ambient atmosphere (Direct Air Capture, DAC).
BECCS is the most prevalent form of negative emissions in emissions scenarios, and I will only refer to BECCS in this blog post. This doesn’t mean other carbon removal technologies are any less important, even if there are economic and biophysical limits, and limited knowledge.
The carbon budget and carbon capture and storage
The total cumulative emissions from 2016 onwards, according to emission scenarios that have a 66% chance of staying below 2°C, has a median of around 950 billion tonnes CO2. This was the value used in the last post, but different estimates can be justified (higher and lower).
Don’t treat 950 billion tonnes CO2 as my preferred carbon budget estimate. Use it as a baseline for the following discussion. The estimate is based on the availability of scenarios with the relevant data.
In the 76 emission scenarios used here, the average cumulative CCS on fossil fuels, from 2016 to the end of the century, is 500 billion tonnes CO2. The average carbon dioxide removal, using BECCS, is another 700 billion tonnes CO2 from 2016 to the end of the century
This extra 1200 billion tonnes CO2, from CCS on fossil fuels and bioenergy (500+700), is not all available to increase fossil fuel use. BECCS can both offset CO2 emissions that have already occurred (such as via fossil fuels) and it can offset hard to mitigate non-CO2 emissions, such as methane in the agricultural sector.
Regardless, CCS on fossil fuels and bioenergy gives a lot of space for the continued use of fossil fuels.
The carbon budget and fossil fuels
The total amount of fossil fuel energy used in the emissions scenarios is equivalent to about 1700 billion tonnes of CO2, certainly much larger than the 950 billion tonnes CO2 indicated by the carbon budget.
CCS on fossil fuels and bioenergy has allowed an extra 750 billion tonnes CO2 of fossil fuels to be used.
This is good news for the fossil fuel industry?
Yes, if society can capture and permanently store 1200 billion tonnes CO2 in the next 100 years. Not to forget sourcing up to 300 exajoules per year of bioenergy.
What if there is no CCS?
The total amount of fossil fuel energy used in the emission scenarios that do not allow the use of CCS reduces to about 900 billion tonnes CO2, much closer to the carbon budget. Not exactly the same, since there are different numbers of scenarios from different models used in the two estimates.
If society wants to stay below 2°C without CCS, there needs to be a rather radical phase out of fossil fuels, starting immediately.
The rather obvious question is whether it is feasible to have such large levels of CCS and bioenergy.
Carbon Capture and Storage
The scenarios that avoid 2°C with a 66% chance, assessed by the IPCC, use CCS at scale. The scale varies by model, though it is unclear why different models produce different levels of CCS.
To put the scale of CCS into perspective, a typical CCS facility today might store 1 million tonnes CO2 per year (e.g., Sleipner). Thus, 1 billion tonnes CO2 per year would require about 1,000 facilities. It is not unusual for models to be using 15 billion tonnes CO2 per year of CCS, which is perhaps 15,000 facilities.
This scale is not tinkering around the edges!
Back when there was considerable momentum for the development of CCS at scale, in the late 2000’s, the International Energy Agency (IEA) scenarios had CCS of about 10 billion tonnes CO2 per year in 2050. This is at the low end of the scenarios assessed by the IPCC.
The current IEA 2°C scenario (with a 50% chance) has CCS of about 6 billion tonnes CO2 per year in 2050.
Today, we have capture capacity of about 0.028 billion tonnes CO2, but only about 0.0075 billion tonnes CO2 are monitored and verified. These are small numbers, particularly in relation to what is required.
It is easy to get carried away with the discussion on CCS, and neglect the required scale of bioenergy. The emission scenarios generally use around 200-300 exajoules of bioenergy each year from 2050. Our current energy system is about 500 exajoules per year.
This is a lot of bioenergy!
Scientists argue today whether 1 exajoule of bioenergy is carbon neutral, I can just imagine where the discussion will go with 300 exajoules. Depending on the model and type of bioenergy, we are discussing land areas the size of India, give or take.
Today we use about 50 exajoules per year of bioenergy, but much of this is unsustainable traditional bioenergy, such as collecting firewood in poor rural communities.
It so happens that the scale of bioenergy in the emission scenarios is at a level where scientists start to disagree on the level of sustainability.
Moral to the story
Carbon Capture and Storage (CCS), on both fossil fuels and bioenergy, almost doubles the amount of fossil fuels that can be used in emission scenarios consistent with a 66% of avoiding 2°C of global warming.
The problem is, we don’t really know if we can source sufficient carbon-neutral bioenergy or get CCS to work at such scale. Earlier, together with Kevin Anderson, we called this combination a moral hazard.
If we base today’s decisions on levels of bioenergy and CCS that may not be feasible, then it is future generations that will pay the price.
There is clearly a lack of literature on how we can achieve such high levels of CCS and bioenergy in practice. Perhaps this is because the answer may be inconvenient.
This blog post was based, in part, on a presentation at the Norwegian Parliament on The Paris Agreement and Norwegian Petroleum Politics.