To limit warming to 2 °C, how much less oil, gas and coal are missing?<

A third of the oil reserves, half of those of gas and more than 80 % of those of coal will have to remain unexploited, if we want to avoid overheating of the planet.It is the shock therapy prescribed by two British researchers in a study published in the edition of the journal Nature of Thursday, January 8.It is a radical weaning for a global economy marked by its addiction to fossil resources.However, the recommended treatment is differentiated according to the large production areas, which makes it all the interest of this work.

Le Groupe d'experts intergouvernemental sur l'évolution du climat (GIEC) a prévenu : pour conserver au moins une chance sur deux de contenir la hausse des températures à la fin du siècle sous la barre de 2°C par rapport à la période préindustrielle – seuil de danger retenu par la communauté internationale en 2009 –, les émissions mondiales de CO₂ ne devront pas dépasser, entre 2011 et 2050, une fourchette allant de 860 à 1 180 milliards de tonnes, ou gigatonnes (Gt).

Refrain from extracting most of the fossil reserves

Or, les réserves fossiles du globe représentent un stock d'environ 2 900 Gt de CO₂ – près de trois fois plus que les émissions tolérables donc –, selon les estimations des auteurs qui se fondent notamment sur les évaluations du World Energy Council, de l'Institut d'études géologiques des Etats-Unis et de l'Institut fédéral allemand pour les géosciences et les ressources naturelles. Encore ne s'agit-il que des réserves, c'est-à-dire des volumes récupérables aux conditions techniques et économiques actuelles, dans des gisements déjà exploités ou en voie de l'être. Les ressources, elles, c'est-à-dire l'ensemble des matières fossiles présentes dans le sous-sol terrestre, sont près de quatre fois plus importantes (environ 11 000 Gt).

The conclusion is essential: it is necessary, up to 2050, refrain from extracting and burning most of the fossil reserves.The originality of the study of the two researchers, Christophe McGlade and Paul Ekins, of the University College London, is to have sought to quantify the necessary "sacrifice", depending on the countries or sets of countries, but also by distinguishingBetween conventional or unconventional oil, conventional or unconventional gas, and coal.

To do this, they turned a technical-economic model used by energy.This combines a series of parameters characterizing the major regions of the world-reservations, extraction, transport, transformation and uses of different energy sources, existing and future technologies, balance between supply and demand, exports, etc."Optimize" the global energy system.In other words, to obtain a minimum energy cost.To this model, they added an additional constraint: the limitation of warming to 2 ° C.

Effort unevenly distributed depending on the country

Résultats : 35 % des réserves de pétrole, 52 % de gaz et 88 % de charbon doivent rester sous terre. Le recours au captage-stockage du CO₂ – une technologie encore embryonnaire – ne permettrait qu'une faible diminution de ces pourcentages (respectivement 33 %, 49 % et 82 %). Mais l'effort est inégalement réparti. Les pays producteurs du Moyen-Orient, qui possèdent l'essentiel des réserves, doivent renoncer à 38 % de leur pétrole et 61 % de leur gaz, l'Afrique à respectivement 26 % et 34 %, la Chine et l'Inde réunies à 25 % et 53 %, l'Europe à 21 % et 6 %, les pays de l'ex-Union soviétique à 19 % et 59 %.

Canada has to deprive itself of 75 % of its oil and 24 % of its gas.On the other hand, the United States almost escapes these restrictions, since it should only abandon 9 % of their oil deposits and 6 % of those of gas.What the authors explain by the proximity of the production and consumption centers which reduces costs.But it is for coal that, everywhere, restrictions are the most drastic, the Middle East even ahead of 99 %in the ground.

Let sleeping unconventional hydrocarbons sleep

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As for the particular case of unconventional hydrocarbons (oil and shale gas, bituminous sands), the authors conclude that an increase in their current production is incompatible with the desire to curb warming.This would therefore penalize the American production of gas and shale oils and that, Canadian, of bituminous sands.Likewise, they underline, "all the resources of the Arctic in hydrocarbons should be classified as non-burning".

"Politicians must realize that their instinct consisting in resorting to fossil fuels available on their territory, is incompatible with their commitment to hold the objective of 2 ° C," concludes Christophe McGlade.

"Compensation between winners and losers"

Roland Vially, géologue à l'IFP Energies nouvelles, prend des distances avec l'étude. Il met ainsi en cause la pertinence de l'utilisation, sur ce sujet, d'un modèle d'optimisation économique. A ses yeux, « il aurait été plus intéressant de faire une optimisation en termes d'émissions de CO₂ plutôt qu'en termes de coût ».

"There is a big absent in this article: the consumer," he also observes.The producing countries are implicitly made responsible for global consumption, while it takes [to remain under the limit of 2 ° C] that consumer countries consume less and therefore that demand decreases ”.

Researcher at the Potsdam Institute for Climate Impact (Germany), Jérôme Hilaire, co -signs with his colleague Michael Jakob of a commentary in the same number of nature, judges this work "very interesting", insofar as he is "the firstTo be identified in a so detailed way where the fossil reserves and resources not to be exploited. ”Above all, he adds, these results highlight the need for climatic policies providing for "a compensation system between winners and losers".

It is difficult to see how - and the study does not provide the answer - convince a producing country, rich or poor, or an oil or gas company, to give up the pension of hydrocarbons, without the implementation of mechanisms such asThat a global carbon market, or the Green Climate Fund, intended to help developing countries take their share in the fight against warming.Questions that will be at the heart of the Paris World Climate Conference in December 2015.

Pierre Le Hir

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