Imperativ čisté nuly

OXFORD – Svět dospěl k historické dohodě o klimatických změnách. Dohoda uzavřená na pařížské konferenci OSN o změnách klimatu zavazuje státy, aby podnikly kroky k omezení globálního oteplování na úroveň „výrazně pod“ 2º Celsia oproti předindustriálnímu období a aby vynaložily „úsilí“ o omezení oteplování na úroveň 1,5º Celsia. Zároveň zavazuje rozvinuté země, aby poskytovaly rozvojovým zemím pomoc ve výši 100 miliard dolarů ročně. Ze závěrečných vyjednávání bohužel vypadlo jediné číslo, které má pro budoucnost naší planety skutečný význam: nula.

Takové je čisté množství oxidu uhličitého, které můžeme emitovat, máme-li někdy stabilizovat teplotu planety na jakékoliv úrovni. Nula, nic, nicka. Planetární systém atmosféra-oceán je jako vana, která se plní CO2 a dalšími skleníkovými plyny: čím vyšší je jejich hladina, tím teplejší planeta bude.

Kohoutek emisí se musí zcela uzavřít, jakmile vana dosáhne hladiny spojené s určitou úrovní oteplení – řekněme 2ºC, nad kteroužto hodnotou začínají podle téměř jednomyslného názoru vědců hrozit vážná rizika, vzniká možnost zlomových bodů a adaptační schopnost civilizace přestává být zaručená. Jinak se atmosférická vana bude plnit dál a oteplovat planetu o 3º, 4º, 5º a tak dále, až emise konečně ustanou – nebo až vyhyneme. Čím dříve kohoutek uzavřeme, tím na nižší teplotě se klima stabilizuje, tím menšímu riziku budeme čelit a tím nižší budou náklady naší adaptace na teplejší planetu.

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