The announcement was enough to be discouraged. In January, researchers from the University of Cambridge, UK, looked at the effectiveness of attic and wall insulation measures in England and Wales on reducing gas consumption in households, with a striking observation: four years after the works, almost all the energy savings have been cancelled. In question, according to the researchers, the change in behavior, including the increase in heating, or the opening of the windows when it was too hot, or even the extensions of buildings which could have contributed to canceling the reductions in gas consumption. .
While the energy crisis is hitting the United Kingdom hard and the thermal renovation of housing appears to be crucial for reducing our energy consumption, the results of this study could cause us to give up. However, they testify to a reality well known to researchers called the “rebound effect”. A phenomenon by which the improvements obtained in terms of energy efficiency and production are compensated, partially or totally, by an adaptation of society.
“This phenomenon is at the heart of current issues, and yet we talk about it very little”, is surprised Pierre Veltz, sociologist and economist, professor emeritus at the Ecole des Ponts ParisTech who has written a book dedicated to this question. (“Bifurcations: reinventing industrial society through ecology”). While the reduction of our greenhouse gas emissions depends largely on lower consumption and energy efficiency measures, the rebound effect appears as a specter threatening our efforts.
The market economy in question
This “energy efficiency paradox” was first demonstrated in the 14th century by the English economist William Stanley Jevons. In his book, The coal issue, he demonstrates how, despite the appearance of a new, more efficient and less coal-consuming steam engine, there has not been a decline in the use of this energy, but a continuous increase due to the mass production of more powerful machines. Whose fault is it ? Partly to the market economy. By reducing the cost of goods and services through efficiency, demand increases. And if we add to that advertising, and the efforts of companies to sell these products, the effect is further reinforced.
In his book, Pierre Veltz explains that aluminum cans have been greatly improved in recent years: there is much less material used in the manufacture of a part. But the number of cans sold in the world has grown so much that the consumption of steel or aluminum for cans has soared. In the same way, very significant gains have been made in recent years in the consumption of kerosene by aircraft, but air traffic has increased so much that these gains have been drowned out in traffic. Thus, while the volume of greenhouse gases emitted per passenger-kilometre decreased by half, the total volume of emissions was multiplied by two, he underlines in his book.
too much sophistication
In recent years, it is also in the digital sector that the rebound effect has been the most spectacular. “Computers are more and more powerful, the result is that consumption has exploded, especially in video, which implies larger server farms, and has the consequence of drastically increasing energy consumption”, underlines Peter Veltz. The carbon footprint of the sector is thus already higher than that of civil aviation. In a 2020 reportthe Shift Project thus notes that the current growth of the sector is “unsustainable”, being built “around economic models which make profitable the increase in the volumes of content consumed and terminals and infrastructures deployed”.
But that’s not all. The rebound effect is also characterized by the complexity of the products we have developed over the past decades. A sophistication of ordinary products that has led to a multiplication of components. “The efficiency gains have been recycled in the increase in demand, but also in the increase in the complexity of the products”, explains Pierre Veltz. The researcher cites cars, which are now made up of more than 1,500 chips, “some of which are necessary for safety and comfort, but how many others are useless?”.
How to avoid putting down all these efforts in the reduction of our energy consumption, and our emissions? By trying to influence behavior, and moving towards more sobriety, argue the experts. “We can clearly see that the rebound effect has been part of the functioning of the market economy for so long, that if we don’t play on consumption, we won’t be able to stem it”, underlines Pierre Veltz. For the digital sector, this would mean choosing: equipping yourself less but better, and questioning “collective technological choices”, says the Shift Project. The key to this dilemma lies above all in our behavior. “The rebound effect is not absurd, it is in the market logic of the economy, and we cannot prohibit companies from selling more. The only way to do it is to act on consumption and therefore to go towards sobriety”, pleads Pierre Veltz.