Svet, toplejši za 4°C

Kako verjeten je svet 4°C? Zaveze, ki so jih države izrekale na podnebnih pogajanjih v Copenhagenu in Cancunu, bi, če bi se jih v celoti držali, svet umestile na smer povprečnega globalnega segrevanja za več kot 3°C. A celo če bi bile te zaveze v celoti implementirane, bi še vedno ostala okoli 20-odstotna možnost, da bi segrevanje preseglo 4°C do l. 2100 in 10-odstotna možnost, da bi se to zgodilo že do l. 2070, če bi emisije sledila srednjemu business-as-usual referenčnemu poteku. Po scenariju z višjo intenzivnostjo uporabe fosilnih goriv, kakršen je IPCC scenarij SRESA1F1, segrevanje preseže 4°C že prej v tem stoletju. Vendar je  potrebno opozoriti, da se takšnim stopnjam segrevanje še lahko izognemo. Obstajajo tehnično in ekonomsko izvedljivi scenariji izpustov, ki bi še vedno lahko omejili segrevanje  v 21. stol. na 2°C ali manj. (Poročilo WB Turn Down the Heat: Why a 4°C Warmer World Must be Avoided str. 23, provizoričen prevod LO)

Kakšne bodo posledice in kako bo živeti v štiri stopinje toplejšem svetu? Bistveno povečanje pogostosti vročinskih ekstremov,

The authors’ statistical analysis indicates that monthly heat extremes will increase dramatically in a world with global mean temperature more than 4°C warmer than preindustrial temperatures. Temperature anomalies that are associated with highly unusual heat extremes today (namely, 3-sigma events occurring only once in several hundreds of years in a stationary climate) will have become the norm over most (greater than 50 percent) continental areas by the end of the 21st century. Five-sigma events, which are now essentially  absent, will become common, especially in the tropics and in the Northern Hemisphere (NH) mid-latitudes during summertime. …Prolonged heat waves are generally the most destructive as mortality and morbidity rates are strongly linked to heat wave duration, with excess deaths increasing each additional hot day  Temperature conditions experienced during these recent events would become the new norm in a 4°C warmer world and a completely new class of heat waves, with magnitudes never experienced before in the 20th century, would occur regularly. (str 59, 62)

naraščanje gladina morja

Warming of 4°C will likely lead to a sea-level rise of 0.5 to 1 meter, and possibly more, by 2100, with several meters more to be realized in the coming centuries. Limiting warming to 2°C would likely reduce sea-level rise by about 20 cm by 2100 compared to a 4°C world. However, even if global warming is limited to 2°C, global mean sea level could continue to rise, with some estimates ranging between 1.5 and 4 meters above present-day levels by the year 2300. Sea-level rise would likely be limited to below 2 meters only if warming were kept to well below 1.5°C.

in pospešeno zmanjševanje biotske raznovrstnosti

In fact, in a 4°C world climate change seems likely to become the dominant driver of ecosystem shifts, surpassing habitat destruction as the greatest threat to biodiversity. Recent research suggests that large-scale loss of biodiversity is likely to occur in a 4°C world, with climate change and high CO2 concentration driving
a transition of the Earth´s ecosystems into a state unknown in human experience. Ecosystem damage would be expected to dramatically reduce the provision of ecosystem services on which society depends (for example, fisheries and protection of coastline— afforded by coral reefs and mangroves).

so le nekatere izmed številnih neugodnih posledic podnebnih sprememb, ki jih navaja poročilo.
Ampak ključno sporočilo je nedvomno tole. Res je, da podnebnih sprememb ne moremo več preprečiti. Vendar obstaja bistvena razlika med posledicami, ki jih bo imelo segrevanje za 1,5°, 2° ali 4° in več. Tu pa manevrski prostor še obstaja in nam omogoča delovanje, ki bo odločalo  o velikosti škode, s katero se bodo spopadali naši otroci.
Ampak kako sploh lahko delujemo? Recimo v tem trenutku svetovna premogovna industrija načrtuje gradnjo novih 1200 termoelektrarn na premog. Njihov skupni izpust CO2 bo primerljiv z celotnim izpustom CO2 v ZDA (ki danes predstavlja blizu 20% svetovnih izpustov), navaja Greenpeace. Eno izmed teh elektrarn gradimo tudi v Sloveniji. Koliko smo in koliko bomo naredili, da jo preprečimo?