Détrôner le roi Charbon

MELBOURNE – Cette année, la consommation de dioxyde de carbone dans l’atmosphère a atteint le seuil de 400 parties par million (ppm). Le taux de CO2 dans l’air n’avait pas été aussi élevé depuis trois millions d’années, époque à laquelle le niveau des mers était supérieur de 24 mètres à celui que nous connaissons. Aujourd’hui, le niveau des mers augmente à nouveau. En septembre dernier, la banquise arctique couvrait la plus petite surface jamais enregistrée. À l’exception d’une seule, les dix années les plus chaudes depuis 1880, année du début de l’enregistrement des mesures mondiales, ont eu lieu au cours du XXIe siècle.

Certains climatologues considèrent que ce taux de 400 ppm de CO2 dans l’atmosphère est d’ores et déjà suffisant pour nous faire franchir un seuil critique au-delà duquel nous risquons une catastrophe climatique susceptible de contraindre des milliards de personnes à l’exode. Ces scientifiques estiment qu’il est nécessaire que nous réduisions le taux de CO2 dans l’atmosphère à 350 ppm. Ce chiffre a donné lieu à l’initiative baptisée 350.org, un mouvement populaire qui réunit les volontaires de 188 pays dans le but de résoudre le problème du changement climatique.

D’autres climatologues sont plus optimistes : ils considèrent que si nous permettons au taux de CO2 atmosphérique d’augmenter jusqu’à 450 ppm, niveau associé à une élévation de température de 2° Celsius, nous avons 66,6% de chance d’éviter la catastrophe. Ce qui revient tout de même à une chance sur trois de subir le désastre – soit une probabilité encore moins heureuse qu’à la roulette russe ; sachant par ailleurs que nous prévoyons de dépasser le taux de 450 ppm d’ici 2038.

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