Hydrogen leakage warms the climate

January 2, 2023 at 4:43 p.m.
Updated January 3, 2023 at 6:26 p.m.

Reading time: 5 minutes

Energy Climate

No, hydrogen is not climate neutral. According to a new study published in the scientific journal, the global warming potential of hydrogen reaches a value of 12.8 (± 5.2) in 100 years. Communication Location and Environment November 26. In other words, 1 ton of hydrogen released into the atmosphere is equivalent to releasing about 13 tons of carbon dioxide. That is, climate results twice as high as the first estimates dating back to the early 2000s.

Bad news for industrialists and governments dreaming of the tiny molecule of hydrogen. Today, several sectors of heavy industry and transport – automobile, rail, marine and even aviation – rely on the availability of this fuel, which CHO₂ when consumed, to meet carbon reduction goals.

Especially since almost all of the hydrogen currently consumed in the world is produced from fossil sources and especially through a very polluting process “ methane steam reforming », requires natural gas. The first challenge for hydrogen to gain interest in the energy transition is to introduce a new low-carbon hydrogen industrial sector in record time. President Emmanuel Macron even promises “ Making France the world leader in hydrogen “green” »hydrogen is produced using renewable electricity.

Implementing a hydrogen-based economy” green “, it is planned to create huge solar and wind farms, especially dedicated to hydrogen production” green “. Here is a photovoltaic park in the Southern Alps. © Vincent Verzat/Reporterre

In fact, this rapid industrial deployment requires the creation of numerous infrastructures to produce, transport, store and use this energy carrier. However, as with any industrial gas, a small fraction of the hydrogen produced will escape the various equipment that make up the value chain. “ Especially since hydrogen is a small molecule, it diffuses easilyChristophe Coutansu, professor at the University of Poitiers and member of the Hydrogen Federation of the National Center for Scientific Research, says.CNRS). Hence the interest of this serious study, which reminds us that it is necessary to limit the leakage of hydrogen as much as possible, from the production of this energy vector to its use. »

Greenhouse gas violation

The authors of the study recently went through a model of atmospheric chemistry. “ This explains the difference of two factors with the first calculations based on the old model. », – says climatologist Didier Hauglustaine. Because hydrogen, which has a lifespan of only two and a half years in the atmosphere, is not a greenhouse gas like others: “ It is an indirect greenhouse gas: it disrupts the concentration and lifetime of other greenhouse gases, so it must be estimated by an atmospheric chemistry model. »climatologist summarizes.

In particular, hydrogen, even produced using renewable energies, contributes to global warming by altering methane concentrations (CH₄) directly causes a strong greenhouse effect. The dihydrogen molecule is actually oxidized in the atmosphere by reacting with the hydroxyl radical.OH). That’s why it’s a little short OH to destroy methane molecules. “ This is the main mechanism that explains the heating power of hydrogen », explains Didier Hauglustaine. The oxidation of hydrogen also reacts with atmospheric acid, which contributes to the production of ground-level ozone, another greenhouse gas. Finally, in the presence of hydrogen, methane itself, whose lifetime in the atmosphere increases, forms ozone and water vapor in the stratosphere, gases with radiation properties.

hydrogen” green will be in limited quantities and should therefore be reserved for sectors that are difficult to decarbonise, such as heavy industries (here an ironworks in Luxembourg). Wikimedia Commons/CC BY–HIM 3.0/VT98Fan

Using these newly calculated values, the scientists estimated the climate benefits of deploying the hydrogen sector based on official scenarios developed by the Hydrogen Council – a global lobby for the sector, the International Energy Agency and the European Union. Result: When leaks are between 1 and 3 % of hydrogen produced, transported and used, hydrogen usage “ green »that is, it is produced through renewable electricity, allowing to avoid 90 to 99. % of emissions CHO₂ in a given sector compared to the use of fossil fuels.

On the other hand, the climate interest of hydrogen “ blue »It is questionable whether steam methane reforming (production of hydrogen from natural gas currently in use) associated with carbon capture and sequestration is a highly polluting process. In the scenario where 60 % of hydrogen used “ blue » and the remaining third comes from renewable electricity, the amount of emissions CHO₂ It is avoided by the sector, which is thought to reach only 3 to 61 % compared to the use of fossil resources, the hydrogen leakage rate is always between 1 and 3 %. Discussion: methane leakage inherent in hydrogen production by steam reforming of methane.

“ The higher the share of blue hydrogen in the energy mix, the lower the climate benefit. We are interested in leaning as much as possible towards a hydrogen economy derived from renewable energies »concludes Didier Hauglustaine.