Since no one has yet mentioned it, you might find this http://www.gbn.com/consulting/article_details.php?id=113&breadcrumb=ideas of interest - Peter Shwartz' 2010 update to his 1991 book 'The Art of the Long View'- it built on the scenario planning work originally done at Shell - when making decisions about which oil field investments to make, it helped to extrapolate forward for things like 30 year population demographics, climate changes, and political risk.
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