Lifecycle of energy economies

Heard on the BBC today morning, spoken by someone high up at the AAAS (President?) . I am paraphrasing. "The global energy systems investments (oil rigs, coal mines, distribution, refineries, etc) are about 12 trillion dollars and it takes about 30 to 40 years to change their character (from coal and oil to, say, renewables)." I couldn't get a confirmation on the numbers I heard but the numbers are quite startling nevertheless. Even more surprising is that the change could happen within our generation - has to happen within our generation.

I was rummaging at the BBC and landed at The Green Room, a series of thought-provoking environmental opinion pieces, the blurb sez. Give it a read.