How to best use our carbon budget?

April 07, 2023 Energy

The tons of CO2 that our atmosphere can still absorb are counted if we want to contain global warming. This carbon budget forces us to optimize the use of fossil energies. Some choices have to be made, and they are not trivial.  


1000 gigatons. This is the amount of CO2 that can still be emitted while limiting global warming to 2 degrees, according to the last IPCC report. It falls to about 400 gigatons if the target is set at 1.5 degrees. This carbon budget for humanity can seem significant but it is quite low regarding what has emitted done in the past. We have already released 1000 gigatons of CO2 over the past 30 years. At the current rate of emissions, our carbon budget will be exhausted within 5 years for a temperature increase of 1.5 degrees, and 20 years for 2 degrees. We therefore have little time left to achieve carbon neutrality. Until then, in a world where fossil fuels are still necessary, we have to optimize our exploitation to make better use of our carbon budget. Coal, oil or natural gas, all of these fossil energies are not equal regarding CO2 emissions, whether it is when they are extracted or combustion. We will have to make choices.  


Coal, out! 

The first thing to do is to get rid of coal. It is, by far, the worst fossil fuels in terms of environmental impacts. It produces twice as much as natural gas, and one third more than oil per unit of energy. Its combustion deteriorates air quality through the emission of fine particles and sulfur oxides, which is one of the main causes of death in the world, and of loss of biodiversity linked to acid rain. Coal is also dominated in its use by other fossil fuels. Gas-fired power plants are much more flexible than those that burn coal to produce electricity. And therefore, better able to overcome the problem of intermittency of wind and solar energy. Oil is still irreplaceable in transportation.  

The only good think about coal is that it is an abundant and cheap resource. And that’s the whole point. We must ensure that the available coal reserves are not exploited even if they are profitable. Financial compensation will be needed to ensure that emerging countries give up the coal available in their subsoil. This may take the form of contracts such as the Just Energy Transition Partnership signed with South Africa. The “Coal exit” movement, relayed by NGOs, can help by denouncing the responsibility of investors and companies.  


More or less black gold 

Even if we cannot do without oil, at least in the short term, we can still significantly reduce the emissions linked to its extraction. The emission factor of a barrel of oil can vary from simple to double depending on whether it comes from the subsoil of Kuwait or the oil sands of Alberta.  

A recent study by economists Renaud Coulomb, Fanny Henriet and Léo Reitzmann estimates that 10 gigatons of CO2 could have been avoided between 1992 and 2018 if deposits had been selected according to the climate impact of extraction. The authors point to two factors that explain this wasted carbon budget. The first is the lack of a global price for carbon dioxide emissions, which allows oil companies to neglect the carbon footprint of the fields they exploit.  

The second factor is linked with OPEC quotas, which, by artificially increasing princes, make deposits in non-member countries with high emissions profitable. This is the case of the Canadian oil sands. The authors estimate that 7.64 gigatons of CO2 could be avoided by 2050 by optimizing oil extraction while taking into account the climate cost.  

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The energy transition will take a long time. Our economics are still very dependent on fossil fuels and this will continue for at least a decade. Coal, fossil gas and oil are still available in abundance. It is the capacity of the atmosphere to absorb their greenhouse gas emissions that is limited. The scarcity constraint is not under our feet but over our heads. We need public policies to favor the most decarbonized fossil fuels while waiting for their complete disappearance from the energy mix. Let’s not waste the meager carbon budget still at our disposal. 


Published in Le Monde March 31st, 2023
Photo credits: Patrick Hendry