Face à la hausse des cours du pétrole, le salut viendra-t-il des biocarburants ? Aujourd’hui, les biocarburants les plus intéressants sont ceux de deuxième génération, qui s’appuient sur des sous-produits de l’agriculture et de l’industrie forestière, sans entrer en compétition avec l’alimentation. Mais dans des pays tropicaux, tels que la Malaisie ou l’Indonésie, la fragmentation des paysages et le taux d’humidité élevé des résidus font rapidement grimper la facture : de quoi affecter la compétitivité de cette alternative.

Les tensions pétrolières causées par la guerre en Iran ont fait remonter le cours du Brent à plus de 100 dollars (ou 85,88 euros) le baril début mars 2026. Depuis, les cours jouent au yoyo en fonction des espoirs diplomatiques. Les flux commerciaux sont en tout cas très loin d’avoir retrouvé leur niveau normal.

Dans ce contexte, les biocarburants – incorporant une part biosourcée, soit bioéthanol soit biodiesel – redeviennent plus visibles. À noter qu’aucun des biocarburants disponibles à la pompe n’est du bioéthanol ou du biodiesel « pur », ils sont toujours mélangés avec des carburants classiques. Ainsi, en France, en 2024, le gazole et l’essence consommés à la pompe comportaient au total environ 9 % d’énergie renouvelable biosourcée.

L’Indonésie et la Malaisie, qui souffrent particulièrement du blocage du détroit d’Ormuz pour leur approvisionnement en pétrole, ont récemment annoncé augmenter la teneur en huile de palme dans leurs biocarburants – au risque de faire grimper le cours de l’huile de palme et d’aggraver la déforestation.

Ces carburants actuels restent, pour l’essentiel, des biocarburants de première génération. Les biocarburants de deuxième génération, issus de résidus lignocellulosiques plutôt que de cultures en compétition avec l’alimentation, paraissent plus désirables. Mais à quelles conditions peuvent-ils être réellement compétitifs face aux carburants issus du pétrole ?

Encore faut-il regarder leurs coûts réels. Nous avons mené plusieurs études en Malaisie qui révèlent l’existence de plusieurs coûts cachés en lien avec la fragmentation du territoire, mais également avec le climat tropical, qui impose de transporter de la matière encore humide, faute de pouvoir la laisser sécher sur place.

Différentes générations de biocarburants

Commençons par rappeler ce qu’on entend par biocarburant de première, deuxième ou troisième génération.

• Les biocarburants de première génération utilisent des matières premières agricoles qui entrent en concurrence avec l’alimentation, par exemple les bioéthanols de betterave, de colza, de maïs ou de blé, ou encore les biodiesels de colza, de soja, ou d’huile de palme.

• Les carburants de deuxième génération, pour leur part, ne sont pas en compétition avec l’alimentation. Ils sont au contraire du recyclage de résidus agricoles ou forestiers, donc essentiellement de la cellulose (pailles, pellets, etc.), ou des huiles de cuisson « usagées » issues de la restauration.

• Ceux de troisième génération (comme les cultures de microalgues), enfin, promettent de s’affranchir de ces limites car elles ne mobilisent pas de surfaces agricoles ou forestières comme les deux premières, mais restent pour l’heure moins stabilisées aux plans technologique et économique.

Dans l’état actuel, les deux premières générations sont les seules réellement maîtrisées à l’échelle industrielle. Le débat porte donc, pour le moment, sur les conditions concrètes de réussite des biocarburants de deuxième génération.

À lire aussi : Carburants de synthèse, biocarburants, kérosène vert… De quoi parle-t-on exactement ?

Premier coût caché la biomasse de deuxième génération : la fragmentation du territoire

La biomasse n’est pas une ressource concentrée. Elle est, pour l’essentiel, répartie dans l’espace, dans des champs et des forêts plus ou moins morcelés. Or, plus une telle ressource est dispersée sur le territoire en petites unités, plus son coût de collecte augmente.

Nos travaux menés en Malaisie montrent que le coût d’approvisionnement augmente à chaque fois que la fragmentation spatiale augmente. Pour un million de tonnes de biomasse effectivement disponible, cela représente plus de 4 dollars (soit 3,44 euros) par tonne par unité supplémentaire de fragmentation spatiale. À titre d’exemple, cette fragmentation spatiale a été évaluée à environ 3,3 dollars pour les déchets forestiers – et même à plus de 6 dollars pour certains déchets de palmiers – contre environ 0,3 dollar pour les scieries productrices de contre-plaqué.

Le reste de la logistique joue tout autant. En effet, le coût d’approvisionnement augmente de plus de 6 dollars (soit 5,15 euros) en moyenne par tonne par tranche de 100 kilomètres de transport. Et l’impact de la taille du camion est tout aussi critique : passer d’un petit camion d’une tonne à un 26 tonnes peut réduire le coût d’environ 84 dollars (plus de 72 euros) par tonne.

Ceci a plusieurs implications importantes. Une biomasse apparemment abondante sur un territoire donné peut être non compétitive si elle est trop morcelée. Inversement, une ressource moins abondante mais davantage concentrée peut devenir plus intéressante au plan industriel.

Cette règle est particulièrement importante en Indonésie et en Malaisie, où les mosaïques tropicales de plantations, forêts, routes et petites unités industrielles n’ont rien à voir avec des territoires plus homogènes que l’on retrouve par exemple dans certaines régions agricoles en Europe et aux États-Unis.

À lire aussi : Forêts et plantations de palmiers à huile peuvent-elles vraiment coexister ? Des résultats prometteurs en provenance de Bornéo

La teneur en eau, un deuxième coût caché

Ce n’est pas tout. Tous les résidus de biomasse végétale contiennent une part plus ou moins grande d’eau.

Or, transporter de l’eau dans la biomasse, c’est consommer davantage de carburant pour déplacer une masse qui ne produira pas d’énergie utile.

D’autres parmi nos travaux montrent qu’en Malaisie, à disponibilité comparable, la paille de riz reste bien plus compétitive que les frondes de palmier, du fait de leur teneur élevée en humidité.

Tous ces facteurs contribuent à faire augmenter le coût de production des biocarburants :

• Quand seule la fragmentation spatiale de la ressource augmente, le coût optimal du biocarburant augmente de 17 %.

• Quand seule l’humidité augmente, il grimpe de 42 %.

• Quand humidité et fragmentation se cumulent, le coût augmente de 69 %. Dans le même temps, la capacité optimale de l’usine de bioraffinerie qui traite ces résidus chute de 36 %.

Sous les tropiques humides, la différence entre matière sèche et matière humide est donc un déterminant majeur pour les coûts. Ce point vaut aussi pour les stratégies combinant plusieurs types de biomasses : mélanger plusieurs résidus n’améliore pas automatiquement la compétitivité. En effet, tout dépend de ce que le mélange fait à l’humidité moyenne.

Nos travaux montrent qu’un approvisionnement industriel de résidus de régimes vides de fruits (EFB) (le nom que l’on donne au sous-produit végétal obtenu après collecte des fruits), à 60 % d’humidité, peut être 31 % moins rentable qu’un approvisionnement combinant à la fois des EFB et des fibres de fruits pressés (sous-produit fibreux obtenu après extraction de l’huile de palme par pressage), dont l’humidité moyenne est de 48 %.

Un approvisionnement mixte peut donc être une excellente stratégie… à condition d’éviter tout mélange qui ajouterait de l’eau à transporter, et annulerait l’avantage attendu.

L’usine optimale n’est pas toujours la plus grande

Il existe enfin un troisième coût caché, lié aux économies d’échelle que l’on imaginerait faire en centralisant le traitement des résidus de biomasse. Il existe, en effet, un concept industriel qui remonte à l’invention du fordisme : plus l’usine est grande, plus l’économie d’échelle est forte. C’est vrai en théorie, mais dans la pratique, cela se vérifie ou non selon les cas.

Concernant les biocarburants, cette règle se heurte rapidement à la géographie réelle des ressources. Plus l’usine est grande, plus il faut aller chercher loin des biomasses plus ou moins humides, fragmentées, potentiellement difficiles d’accès ou coûteuses à prétraiter. Les gains d’échelle en termes de procédés pour la raffinerie peuvent alors être effacés par les coûts amont. C’est pourquoi toutes les biomasses sont d’intérêt variable, selon le contexte.

Dans le cas de la Malaisie et de l’Indonésie, la voie de fermentation de seconde génération est la plus compétitive, avec la paille de riz et la fibre de fruits pressés. À l’inverse, les troncs de palmier et certains résidus d’hévéaculture n’y sont sont pas rentables pour de la bioraffinerie.

Mais dans d’autres endroits, la situation pourra être opposée. La stratégie industrielle ne doit donc pas reposer sur des économies d’échelles maximum, mais sur l’ajustement de la capacité industrielle à la matière réelle disponible sur le terrain, à son humidité, à sa dispersion et à son accès.

Du sur-mesure, plutôt que du prêt à l’emploi

Les biocarburants sont, en général, une excellente solution à l’instabilité des cours du pétrole. Mais ils ne sont pas performants par simple abondance de biomasse. Ils exigent un travail fin d’ingénierie : séchage, points de prétraitement, points de collecte et de regroupement, choix des mélanges, logistique, adaptation de la taille des usines…

Les schémas imaginés pour les grandes plaines homogènes du Midwest américain, où la production d’éthanol est concentrée dans la Corn Belt, ou pour certains contextes agricoles centrés sur le colza ou la betterave en Europe, ne se transfèreront pas tels quels dans les pays tropicaux. En particulier en Asie du Sud-Est, où l’humidité, la fragmentation et les contraintes locales changent toute l’équation.

Les biocarburants ne sauraient se réduire à un simple substitut au pétrole, où l’on déclinerait la même solution partout. Ce sont des solutions régionales, qui ne peuvent fonctionner qu’à condition d’être conçues région par région.

Cet article a été décliné sous forme de chronique radio dans l'émission Le Club de C'est pas du vent, diffusée sur RFI le 27 mai 2026 et disponible sous forme de podcast.

Les auteurs ne travaillent pas, ne conseillent pas, ne possèdent pas de parts, ne reçoivent pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'ont déclaré aucune autre affiliation que leur organisme de recherche.

Europe is staring at a dual crisis it hasn’t managed to solve. House prices across Europe have risen 60 percent and rents 30 percent over the past 15 years, while the number of building permits has fallen 20 percent. The European Investment Bank estimates the EU currently needs 2.25 million additional housing units, roughly 50 percent more than is actually being built. And yet the buildings that do get built remain among the largest sources of greenhouse gas emissions on the continent.

Between 2010 and 2024, construction costs in the European Union rose by 56 percent, and the European Commission expects housing demand to grow by more than two million units per year.

The housing affordability crisis and the climate crisis are not two separate problems. They are one interlocked systemic failure, and Europe’s construction and real estate sector sits at the centre of both.

The challenge: three tensions, one industry

The Architecture, Engineering and Construction (AEC) sector has suffered four decades of productivity stagnation. Complex permitting regimes, fragmented governance, and an industry structure built around one-off projects have prevented it from delivering affordable, liveable, and sustainable homes at scale.

By late 2025, the supply of new housing units in the EU met only 50 percent of actual demand, compounded by soaring costs for labour and materials and a construction sector that has historically struggled with low innovation and productivity.

At the same time, buildings account for roughly 40 percent of Europe’s energy consumption and 36 percent of its CO₂ emissions.

The EU Green Deal, the Circular Economy Action Plan, and the EU taxonomy for sustainable activities are demanding deep decarbonisation – but as theWorld Economic Forum’s Reimagining Real Estate framework (2024) makes clear, technology and sustainability commitments alone are insufficient without a reconfiguration of who builds, who owns, and who governs the built environment. The WEF’s earlier Framework for the Future of Real Estate (2021) similarly warned that affordability and decarbonisation would only align if the industry fundamentally changed its business models and governance structures. Neither framework, however, mapped the concrete alternative pathways by which this transformation might actually unfold.

France is an example which shows how quickly Europe’s housing and climate goals can collide. On April 23 2026, the government announced a housing stimulus bill to accelerate construction, decentralise some decisions, and launch a third urban-renewal programme. Its most controversial proposal would allow F- and G-rated energy-inefficient homes back onto the rental market if owners commit to renovation within three years for houses and five years for apartment buildings. Under current rules, G-rated homes have been barred from new or renewed leases since 2025, with F-rated homes due to follow in 2028. The question is whether enforcement and finance will make renovation real.

Across Europe, governments are trying to expand supply without weakening climate targets. Spain has turned to industrialised construction, using EU funds to build social housing faster and cheaper, while also confronting tourist rentals and a small social-housing stock. Germany faces the opposite pressure: housing completions fell to a 13-year low in 2025, while earlier estimates put annual need at 320,000 apartments until 2030.

At EU level, the Affordable Housing Plan now links faster permitting, renovation and cost-efficient construction. Supply measures increasingly depend on whether governments can integrate affordability with decarbonisation targets.

Four plausible futures for 2040

To address this gap, we conducted a multi-year strategic foresight study with over 30 senior industry experts from across Europe, architects, developers, material suppliers, energy companies, and real estate services firms. Published in the journal Futures our study combines a horizon scan, impact-uncertainty analysis, and three rounds of expert workshops to construct four consistent scenarios for the European AEC industry by 2040.

The scenarios are not predictions. They are structured explorations of four plausible development pathways, each with a distinct logic for how decarbonisation, circularity, and housing affordability might interact under different governance arrangements.

In the first scenario, Giants rule the AEC industry, Big Tech firms and OEM-like construction companies dominate through data-driven, off-site, industrialised building. Homes become subscription services; platforms set the standards and productivity rises sharply. But affordability and tenant agency remain contested, and small firms struggle to survive.

In the second, the Circular Future: a coalition of regulators, financial institutions, and pioneering firms embeds circular principles into planning law, procurement, and finance. Buildings become documented material banks; biomaterials replace concrete; renovation dominates. Progress on carbon and resource targets is strong, but urban affordability challenges persist without deliberate policy attention to housing typologies and ownership models.

In the third, public sector leadership: governments take direct control after market mechanisms fail to deliver at scale. Binding targets, standardised typologies, and public investment programmes drive rapid decarbonisation and housing supply, but at the cost of private innovation and creative experimentation.

In the fourth, the Green energy revolution whereby the rapid decarbonisation of the electricity grid reshapes the entire housing question. Buildings become active nodes in bidirectional smart grids, and operational carbon largely disappears. But attention shifts to embodied carbon, energy poverty, and the distributional effects of a transition that benefits some households far more than others.

The call for action

What our scenario analysis makes clear is that there is no automatic alignment between building more homes, decarbonising the stock, and making housing affordable. The same headline instruments, green finance, circular procurement, digitalisation, lead to very different outcomes, depending on who orchestrates the system and which governance logic dominates. This has direct implications for policymakers, investors, and industry leaders right now.

Three no-regret priorities emerge across all four futures:

• Deep renovation of the existing building stock is non-negotiable in every pathway; the question is only who pays and who profits.

• Digital infrastructure for monitoring energy and material performance is needed regardless of which actor is in charge.

• And new skills and organisational capabilities for industrialised construction and lifecycle thinking must be built now, not after the transition has arrived.

The EU’s first Affordable Housing Plan, launched in late 2025, and the upcoming first-ever EU Housing Summit in 2026 offer a rare political window. The question is whether policymakers will use it to address the structural governance failures our scenarios reveal, or simply add more instruments to a system whose fundamental tensions remain unresolved.

The building industry has a decade and a half to get this right. The futures exist; the choices are ours.

A weekly e-mail in English featuring expertise from scholars and researchers. It provides an introduction to the diversity of research coming out of the continent and considers some of the key issues facing European countries. Get the newsletter!

Les auteurs ne travaillent pas, ne conseillent pas, ne possèdent pas de parts, ne reçoivent pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'ont déclaré aucune autre affiliation que leur organisme de recherche.

During the entire course of World War I, approximately 25,000 American women crossed the Atlantic Ocean to attend to the needs of wounded soldiers and civilian communities in Europe. Women traditionally operated in medical units and helped care for wounded soldiers. Following US entry in the conflict, the newly established Women’s Overseas Hospitals and the American Women’s Hospitals in France drew hundreds of trained nurses to get involved in the war effort. Women’s participation, however, was not limited to the medical field. Female physicians and stenographers brought valuable skills to the front and helped the US military in a variety of domains. In 1918, for instance, the US Army Signal Corps sent 223 trained telephone operators to France to take over from inexperienced soldiers who were struggling to keep general headquarters connected with the troops who were under fire.

At a time when women experienced domestic confinement within their homes, taking part in relief organisations and being actively involved on the Western Front gradually reinforced their quest for equal rights, furthered their political agenda, and strengthened their claim for full citizenship.

Many American women seeking meaningful wartime jobs in France came from a very specific background, and many “hoped that the war would prove the forcing house in which long-standing feminine aspirations for the vote and economic equality would finally mature”.

Considerations for telling the story of the mothers to ‘America’s French orphans’

Any course focusing on American women in World War I should acknowledge the social backgrounds of the American wealthy expatriates, businessmen’s daughters, leisured wives of diplomats, and middle-class professionals who served as doctors, nurses, ambulance drivers, stenographers, and radio operators.

When teaching World War I in relation to 20th century American history to high school pupils and undergraduate students, educators traditionally focus on the neutrality of the United States and then expand on the reasons why Woodrow Wilson gradually dragged his country into the global conflict (Editorial note – For further reference: The Path to War: How the First World War Created Modern America by Michael S. Neiberg, Oxford, 2016; Neutrals, Belligerents and the Transformation of the First World War by Abbenhuis Maartje and Ismee Tames, London: Bloomsbury Academic, 2022).

Military historians linger on battles, strategies, and the decision-making process; cultural history gravitates around cultural encounters, war atrocities, and public reaction to the outbreak of the conflict; and scholars specialised in diplomacy dig into government archives, private papers, and conference proceedings to determine the responsibility of each country. But historians of women, childhood, and philanthropy have much to add to the understanding of WWI.

Presenting the big picture fatally necessitates omitting important details, but in the case of World War I studies, some entire facets of the conflict have been overlooked.

Out of interest in humanitarian organisations that operated in my home country, France, between 1914 and 1921, I have recently shifted the focus of my teaching to the plight of children during World War I. Cultural historians have long demonstrated that the French school system mobilised its youth to perpetuate a sense of national belonging in wartime and how state propaganda shaped children’s worldview. Yet I find that the various pictures of the conflict remain ethnocentric and neglect the silent but vital action of American women in rescuing France’s children.

Between 1914 and 1921, thousands of American women acted as mothers for French children displaced by the war.

In 1915, a group of American philanthropists envisioned the creation of Franco-American colonies to rescue youngest war victims from starvation and misery.

Twenty-eight colonies were established by the Committee Franco-American for the Protection of the Children of the Frontier (CFAPCF) to shelter displaced orphans from France and Belgium. All the colonies were managed and staffed by French nuns, but heavily depended on American donations and volunteers – American women. Among them were Alma A. Clarke, a former student at Bryn Mawr College, and Erica Thorp de Berry, the granddaughter of Henry Wadsworth Longfellow, a Harvard University professor and a towering figure in 19th century American literature.

American women helped to feed, educate, and nurse the orphaned and traumatised children who were moved to the colonies to recover and prepare for life on their own after the war. They tucked little orphans into bed, kissed them goodnight, told them stories of the gigantic country across the Atlantic Ocean, and even sang songs when they could not sleep.

Colonies operated as “humanitarian wombs” and though the survival of approximately 800 children from France and Belgium could look relatively insignificant, they carried out the first humanitarian actions toward children.

That same year, in 1915, another humanitarian organisation reached out to thousands of Americans.

Envisioned by Paris-based French industrialist, Émile Deutsch de la Meurthe, the Fatherless Children of France Society (FCFS) encouraged Americans to “adopt” France’s children who had lost their fathers to the war. Although considered orphans by virtue of being fatherless, the children were not “adopted” but rather sponsored at the rate of $36.50 per year (what would be today $900/€773). Though the tireless and skilled efforts of the FCFS staff and volunteers (mainly women), between 1915 and 1921, some 300,000 French children were spared hunger and destitution because they were sponsored by Americans.

Both organisations drew Americans’ financial support and mobilised hundreds of women across the United States. To engage donors and volunteers, they organised fairs on July 4 to remind Americans of Lafayette’s role in the American War of Independence, and spurred Americans to contribute to France’s survival. In the aftermath of the war, mourning families and those who had served were moved to support the cause of the FCFS.

The Fatherless Children of France Society more than doubled the number of sponsorships between November 1918 and January 1921, the date the organisation officially ceased to exist.

American women’s roles in reforging post-WWI communities

In the years after the war, individual Americans helped rebuild devastated France. American women set up schools and reconstructed devastated villages. For example, the American Committee for Devastated France (ACDF), co-founded by Anne Morgan, the daughter of American financier J.P. Morgan, operated on several fronts. From the Château de Blérancourt, some 350 French-speaking American women joined her task force. Among them were Mary Carson Breckinridge, the daughter of an Arkansas congressman and future founder of the Frontier Nursing Service; Lucile Atcherson Curtis, a militant suffragette who would later become the first female in the US Foreign Service; and Anna Lander West McDonnell, the niece of the first Chief Justice of the Supreme Court of the Territory of Washington.

Though the ACDF’s initial mission was to combat infant mortality, rebuild devastated villages, and finance the reconstruction of the industrial network, children’s well-being rapidly became a focus of the organisation.

The ACDF established a network of public libraries for children in the former occupied zones of Northern France. Jessie Carson became the director of a new American-style network of lending libraries for children. In April 1919, the first reading room for children was opened in the Northern French town of Vic-sur-Aisne.

The ACDF inspired American women at Wellesley, Vassar, Smith, Radcliffe, Stanford and other American colleges and universities to tackle problems related to agricultural production and devastated villagers. For example, in France’s remote and war-ravaged regions, a lack of milk contributed to infant mortality.

Funds from humanitarian organisations brought cows to the devastated regions, where underfed mothers could not breastfeed their babies. In early 1920, in Verdun (Meuse), the American-Franco Children’s League bought several cows, and Miss Butler, the president of the Vassar College unit of volunteers, organised the distribution of milk for babies; at the same time, in Reims (Marne), a “Drop of Milk Institution for Babies” opened, through the efforts of American women.

In short, when it came to humanitarian efforts to shield France’s children from destitution, hunger, and death, American women got the job done. And this is an untold story.

American women’s experiences in humanitarian missions in France during WWI are important for many reasons. First of all, they pave the way for future research on American humanitarian action during the Great War, and complement studies dealing with Franco-American relations.

Additionally, the archives of these associations are a treasure for those teaching history at the K-12, college, and graduate levels, as they contain letters from the women serving in France during and after the war. These primary sources are important first-hand accounts of the conflict.

For example, in teaching my unit on American action in France during WWI, I invited my pupils to analyse several fragments of Anne Morgan’s letters to her mother, held at the Morgan Library and Museum in New York City. Her letter, dated April 30, 1919 (Anne Tracy Morgan Papers,1888–1952, Morgan Library and Museum, New York), read as follows:

“We had proudly repaired a room to be used for the school at Camelin, when the Mayor came in and told us that in the brook, just outside the door of the school house, the head of a Boche had appeared in the water, as the brook had washed away the covering of soil that was over the body.”

With all the archives available online and the different tools to communicate, schools and universities in France and in the United States could easily partner with each other on digital projects, along with local repository, library, museum, or university collection.

From across the Atlantic Ocean and from more than a century ago, American women’s voices bearing important witness are still waiting to be heard.

A weekly e-mail in English featuring expertise from scholars and researchers. It provides an introduction to the diversity of research coming out of the continent and considers some of the key issues facing European countries. Get the newsletter!

Emmanuel Destenay ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.