Repensar a Redução de Emissões

HAIA – Tanto nas cimeiras das Nações Unidas sobre as mudanças climáticas como nos muitos fóruns sobre o “crescimento verde”, as energias renováveis e a eficiência energética são consistentemente encaradas como a solução para o aquecimento global. Até a indústria do carvão aderiu à linha da eficiência no seu Comunicado de Varsóvia, emitido antes da cimeira COP19 da ONU do passado mês de Novembro. Mas um olhar mais atento ao sistema energético global, juntamente com um entendimento mais refinado do desafio das emissões, revela que os combustíveis fósseis continuarão provavelmente a dominar durante este século – significando que a captação e armazenamento de carbono (CAC) poderá bem ser a tecnologia crítica para atenuar a mudança climática.

A concentração generalizada na eficiência e na energia renovável deriva da disseminação da Identidade de Kaya, que o economista Japonês Yoichi Kaya desenvolveu em 1993. Kaya calculou as emissões de CO2 multiplicando a população total pelo PIB per capita, pela eficiência energética (utilização de energia por unidade do PIB), e pela intensidade de carbono (CO2 por unidade de energia). Dada a impraticabilidade de reunir apoio para propostas baseadas na gestão da população ou nos limites à riqueza individual, as análises que usam a Identidade de Kaya tendem a ignorar os primeiros dois factores, deixando a eficiência energética e a intensidade de carbono como os determinantes mais importantes das emissões totais.

Mas esta interpretação conveniente não corresponde à realidade. O facto é que a taxa à qual o CO2 é libertado no sistema oceano-atmosfera é várias ordens de grandeza maior que a taxa à qual está a voltar ao armazenamento geológico, através de processos como a meteorização e a sedimentação dos oceanos. Neste contexto, o que realmente importa é a quantidade acumulada de CO2 libertado ao longo do tempo – um facto que o Painel Intergovernamental sobre Mudanças Climáticas reconheceu no seu recentemente publicado Quinto Relatório de Avaliação.

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