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International audience; The concept of energy return (EROEI ratio) is widely used in energy science to describe the interactions between energy and the economic system but it is largely ignored in macroeconomics. In order to contribute to bridging a gap between these fields of research, we incorporate these metrics into an endogenous growth model with two sectors (energy and final goods) and use this model to analyze the macroeconomic implications of a transition to lower EROEI resources. An approach in terms of net energy allows us (1) to explicitly link the EROEI to macroeconomic variables, (2) to show how it is related to the growth rate of GDP and (3) to obtain a closed-form solution for its long-run value at a general equilibrium level. There is furthermore a tight and decreasing long-run relationship between the EROEI value and the share of investment that must be allocated to the energy sector. Hence, a transition to lower EROEI resources intensifies the rival use of capital in the energy and non-energy sectors and leads to major economic changes, both in the inter-sectoral capital allocation and in the allocation of final output between consumption and investment. We show that a protracted economic contraction may occur before the completion of the transition to renewable energy. We analyze how (1) the magnitude of this contraction and (2) the possibility of an ulterior recovery depend on the initial stock of non-renewables, the potentials of technical progress in the energy and non-energy sectors and the substitutability between capital and energy.

Ce numéro spécial de Regards économiques croise les regards d’ingénieurs et d’économistes pour étudier les possibles impacts de la transition énergétique sur la croissance économique. Cette transition peut être définie comme la transformation des modes actuels de production et de consommation de l'énergie. L’angle d’analyse ne concerne pas un pays ou une région particulière mais se situe à un niveau global. Depuis quelques années, certains auteurs ont émis des doutes sur la possibilité de poursuivre sans encombre, à un niveau global, la croissance économique pendant la transition énergétique (TE). Le présent numéro de Regards économiques approfondit certains de leurs arguments à travers deux contributions. La première contribution (par les ingénieurs Elise Dupont, Hervé Jeanmart et Louis Possoz) concentre son attention sur les évolutions attendues du taux de retour énergétique (TRE) des sources éolienne et solaire, ainsi que sur leur potentiel. Les auteurs mettent en évidence un effet «localisation» selon lequel l’expansion de ces énergies impliquera de les installer sur des sites de moins en moins favorables, produisant de moins en moins d’énergie pour la même capacité installée. Une TE vers un monde 100 % renouvelable conduira alors à un TRE du système énergétique global sensiblement plus faible qu’aujourd’hui et ce, malgré le progrès technique dont les auteurs soulignent par ailleurs que le potentiel est limité. Les possibles conséquences macroéconomiques d’une telle TE sont analysées dans la deuxième contribution (par les économistes Jean-François Fagnart et Marc Germain). La baisse du TRE global accompagnant la TE se traduit par l’exacerbation des besoins en capital du secteur énergétique, avec un possible effet «d’éviction» du secteur final au niveau de l’affectation des biens d’investissement. Cet effet pèse négativement sur la croissance économique. S’il est suffisamment fort (ce qui dépend des caractéristiques de l’économie), la TE s’accompagne d’une phase de décroissance économique prolongée. Dans le cas contraire, une transition «en douceur» (c’est-à-dire sans décroissance économique) est possible. Les deux contributions résumées ci-dessus visent avant tout à éveiller la prudence à l’égard d’un certain «optimisme technologique» suggérant que la TE pourrait se révéler sans douleur pour la croissance économique grâce au seul développement tous azimuts des énergies renouvelables. Le message implicite qui en découle est que pour favoriser une transition «en douceur», des changements de comportements à grande échelle sont nécessaires (par exemple, en matière de transport). Ce qui précède pose la question des conséquences de tels changements de comportements sur l’économie, et en particulier sur le PIB et la croissance. Une autre question concerne le rôle que les pouvoirs publics devraient jouer dans la stimulation de ces changements. A notre connaissance, il s’agit là de questions qui restent largement ouvertes.

International audience; In an input–output model of a two-sector economy (energy and manufacturing), we analyse the macroeconomic implications of the quality of secondary energy production. We measure it by the net energy ratio (NER for short), i.e. the fraction of produced energy available for net final production. NER is shown to be related to the EROEI concept encountered in energy science and to affect (a) the energy intensiveness of final output, (b) the capital requirements of the two sectors of the economy and the aggregate capital–output ratio, and (c) the rate of capital accumulation and the growth rate of the economy at given saving rate. As a consequence, an energy transition characterized by a decreasing NER would exert a drag on economic growth.

We reassess Ricardo's conjecture of a secular increase in rent in an endogenous growth model with an essential renewable material resource and rising product quality. The model is consistent with the concept of strong sustainability and thus assumes that the resource productivity is bounded. Hence, only qualitative growth (i.e., a secular increase in the quality of final productions) may persist in the long run. We analyse how the scarcity of the resource affects the rent level and the distribution of national income (between resource, capital and labour) in the short and long runs. In the long run, resource scarcity induces a distributive conflict opposing labour to capital and resource, a lower resource stock implying generally a lower labour share and higher capital and rent shares. The transitory dynamics of the economy is analyzed numerically, starting from initial conditions characterized by a low capital stock and a large potential technical progress. Even if initially the rent share may evolve non-monotonically, simulations tend to confirm that Ricardo's conjecture emerges sooner or later during the transitory dynamics: except in the case of a very high dematerialization potential of final output, the rent share will rise as quantitative growth slows down. JEL: E25, D9, 044, Q0, Q56. / KEY WORDS: Growth, Strong Sustainability, Rent, Functional Distribution of Income, Renewable Resource, Dematerialisation.

International audience; We introduce the concept of product complexity in an endogenous growth model with renewable energy and expanding product variety à la Grossman and Helpman (1991). We describe the complexity of a product as an increasing function of the variety of inputs it consists of. Considering that energy is necessary to all human activities (including research), we highlight what type of long run growth path is possible according to (a) the potential of energy efficiency gains in the various human activities and (b) the effect of the product complexity on the energy intensiveness of its production process. In a finite world, a neoclassical growth path where economic growth can be both quantitative and non-quantitative (i.e. takes the form of an increase in the quantity of produced goods and in the product variety) is only possible if the potential of energy efficiency gains is unbounded in all human activities. If the energy intensiveness of the final production is bounded from below by a strictly positive constant, quantitative growth is not possible in the long run but non-quantitative growth may persist if (i) the impact of product complexity on the energy intensiveness of production is null or weak enough and (ii) the energy intensiveness of research activities tends to zero. If these conditions are not met, no form of long run growth is possible.

We analyse the transition of a decentralized economy whose energy supply switches progressively from non-renewable (NRE) to renewable energy (RE) sources. The two energies are perfect substitutes but RE production offers a lower Energy Return On Energy Invested(EROEI). The transition is characterized by a decreasing trend of the aggregate EROEI and by major changes both in the allocation of output between consumption and investment and in the allocation of capital between energy and final good productions. As a result, the energy transition may (and will usually) be characterized by a non-monotonic evolution of aggregate income and private consumption: after a peak and before the NRE exhaustion, the economy experiences a contraction. We analyze what affects 1) its magnitude and 2) the possibility of an ulterior recovery of income. Incidentally, a complementarity appears between a rapid development of RE production and the availability of NRE: the end of the NRE era puts a drag on the development of the RE production.