Carbon removal - Part 1: the CO2 genie is out of the bottle
To address climate change and limit global warming, we hear every day that we must drastically reduce CO2 emissions and seek to stop them as soon as possible. It’s true but actually, it won’t be enough.
We need something more: large-scale carbon removal technologies.
Part 2: fixing the roof despite a pay cut?
Part 3: starting with the lowest-hanging fruits
The natural carbon cycle maintained an optimal CO2 concentration
Greenhouse gases make our planet habitable by sufficiently warming its atmosphere. CO2 is one of these gases and, as carbon is the 4th most abundant element in the Universe, it’s the most emitted by human activities: CO2 emissions represent more than 80% of all GHG emissions. Put too much CO2 into the atmosphere however and the greenhouse effect becomes unbearable:
- On Mars, the atmosphere contains almost no CO2 and the average temperature is -50 degrees Celsius
- On Venus, 96% of the atmosphere is made of CO2 and the average temperature is +420 degrees Celsius*
*Yes, the distance to the sun also plays a role
On Earth, the share of CO2 in the atmosphere is around 0.4%. In addition to the atmosphere where it is in the form of carbon dioxide, carbon is stored in 3 other locations:
- Biomass (in organic stuff: plant and animal species)
- Oceans (as bicarbonate, carbonate and dissolved CO2)
- Underground (as lime or fossil fuels): by far the largest with around 60 million gigatons (Gt) of carbon stored compared to 40 000 Gt in oceans, 2 500 Gt in biomass and 900 Gt in the atmosphere
In the last few millennia, the system was in equilibrium.
The CO2 concentration within the atmosphere stayed roughly the same as flows between the different storage locations were balanced. For example, biomass absorbs carbon atoms from the oceans and atmosphere through photosynthesis and re-emits them through respiration and decomposition after death (170 Gt of carbon flows both ways each year).
The industrial revolution changed everything
However, as our economy has thrived on a constant flow of energy and material goods, obtained from natural resources such as fossil fuels and biomass, we have added new flows to the natural ones:
- Carbon atoms from underground are released into the atmosphere through the combustion of fossil fuels
- Deforestation and other new agricultural land use schemes have transferred carbon atoms from biomass to the atmosphere, deeper ploughing exposing more humus to decomposition for example
In total, human economic activity involved the emission of 42 Gt of CO2 (12 Gt of carbon) in 2018, of which 37 Gt is emitted by the combustion of fossil fuels.
Natural flows have changed in an attempt to maintain a balance, with other natural sinks (biomass and oceans) absorbing more CO2, but it is estimated that about 45% of CO2 emissions remain permanently* in the atmosphere.
*on the human timescale, as mineral weathering could eventually enable most of this carbon to go back underground, but over millions of years
In 1800, before the Industrial Revolution, the concentration of CO2 in the atmosphere was around 280 parts per million (0.28%). In 2018, it was 410 (0.41%) and it is rising at a rate of approximately 2 ppm/year.
A threshold has already been crossed
The objective of the Paris COP 21 agreement is to limit global warming to a range of 1.5 to 2 degrees C above pre-industrial levels. 2016 was already about 1.1 degrees C warmer than this baseline.
The bad news is that the movement has great inertia: even if we stop emitting greenhouse gases now, the temperature will continue to rise anyway for some time. Moreover, any significant increase will most likely trigger irreversible phenomena, such as the melting of ice caps or the extinction of certain animal and plant species, with likely negative feedback effects on the concentration of CO2 in the atmosphere.
It is difficult to define a “safe” level of CO2, enabling to maintain global warming at sustainable levels (between 1.5 and 2 degrees then) and to avoid the triggering of such ecological disasters.
However, several leading scientists agree on 350 ppm*.
And even then, it is good to remember that the last time the Earth experienced a CO2 concentration between 300 and 400 ppm, the temperature was 2 to 3 degrees C higher than in 1800.
You read correctly, 15% below the current level, 60 ppm less, i.e. about 470 Gt CO2 and 11 years of emissions at the current rate.
Even if we stop all CO2 emissions tomorrow morning, there is probably already too much CO2 in the atmosphere to prevent global warming from eventually exceeding 1.5-2 degrees compared to the pre-industrial era.
Zero CO2 emission is out of reach
And there’s a second major problem. We often hear that renewable and nuclear energy sources will decarbonise our entire economy and ultimately allow us to change only marginally our model of civilisation. It’s wrong.
Even if we imagine that we can overcome the obstacles of storing this intermittent energy source and of its lower average efficiency compared to fossil fuels, and thus make our electricity 100% clean, we must remember that electricity production accounts for only about 20% of the world’s energy consumption and 40% of CO2 emissions.
For many of our industrial processes, producing the raw materials we need (cement, iron and steel, petrochemicals and chemicals), and of our transportation means (aviation, shipping), we have no viable alternatives to fossil fuels.
We will therefore reduce CO2 emissions voluntarily, by decarbonising our electricity and electrifying as many processes as possible, involuntarily due to the gradual drying up of easily attainable fossil reserves, but we will not be able to stop them completely in the near future. Even the most optimistic scenarios do not predict a reduction in emissions of more than 80% by the end of the century: too many of the applications we are not ready to give up depend on fossil fuels.
Our future also depends on carbon removal technologies
To sum up: there is already too much CO2 in the atmosphere to keep global warming within tolerable limits and we will not avoid adding some more, even with our best efforts.
To prevent global warming from becoming unbearable we must therefore:
- reduce carbon-based sources of electricity as much as possible by using renewable & nuclear energy and electrify as many processes as possible
- try to limit practices that will still depend on fossil fuel
But also:
- deploy CO2 removal technologies on a large scale, at least to offset the remaining emissions and, in the long term, to reduce the absolute quantity of CO2 already in the atmosphere
It’s never stressed enough: 101 of the 116 IPCC* models that meet the 2 degrees target, and all of those meeting the 1.5 degrees target, rely on carbon removal technologies on a large scale. Indeed, the IPCC and IEA** estimate that between 4 and 10 Gt of CO2 will have to be permanently removed from the atmosphere every year from 2040 onwards.
*IPCC: Intergovernmental Panel on Climate Change, United Nations body for assessing the science related to climate change
**IEA: International Energy Agency, intergovernmental organization
Is it even technically possible? Is it economically viable? That will be the subject of Part 2.
