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Il grado di sostenibilità dei sistemi socio-ecologici

La quantificazione di tali flussi è fondamentale per ottenere un quadro sul livello di sostenibilità dei sistemi socio-ecologici. È quello di cui si occupa la contabilità dei flussi di materia ed energia (MEFA, Material and Energy Flows Analysis), disciplina nata pochi decenni fa e oggi riconosciuta e impiegata dai principali istituti di ricerca e di statistica di tutto il mondo1.

Attraverso questa metodologia sono state realizzate delle ricerche che hanno stimato e confrontato tra loro i consumi di materia e di energia caratteristici delle tre grandi categorie di sistema socio-ecologico presenti nella storia dell’uomo. La società di cacciatori-raccoglitori ha un consumo medio di energia pro capite all’anno di 10-20 GJ (Gigajoule), la società agricola di 40-70 GJ, la società industriale di 150-400 GJ2. Il consumo di materia stimato è rispettivamente di 1 tonnellata, di 3-6 tonnellate e di 15-25 tonnellate (sempre riferendosi al periodo di un anno e relativamente a una persona). Questi dati mostrano che la transizione dal sistema agrario a quello industriale è associata ad un incremento medio nei consumi pro capite di energia e materia di 3-5 volte. L’aumento reale dei consumi è ancora superiore se consideriamo che tale transizione è inoltre associata ad un incremento medio della densità di popolazione di 10 volte (si è passati da 40 a 400 persone a Km2). A completare il quadro, la percentuale di popolazione che si occupa di agricoltura è passata da più dell’80% (nel sistema agricolo) a meno del 10% (nel sistema industriale). La produzione di biomassa è aumentata, ma mentre nel sistema agrario rappresentava più del 95% dell’energia totale impiegata, in quello industriale rappresenta solo dal 20 al 30% (Krausmann 2008).

A cura di Alice Benessia, Maria Bucci, Simone Contu, Vincenzo Guarnieri.


1 In particolare l’MFA, la metodologia di analisi dei flussi di materia, è oggi la principale metodologia di contabilità ambientale fisica impiegata ufficialmente dalle ricerche compiute da Istat, Eurostat e da organizzazioni internazionali come l’OCSE.

2 I dati si riferiscono all’indicatore di contabilità ambientale DEC (Domestic Energy Consumption) e al DMC (Domestic Material Input)


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