Robert Shiller says when it comes to commodity prices, images that portray the earth as small and vulnerable matter:

 

Seeing is believing, by Robert Shiller, Project Syndicate: Could the television image we’ve all seen of the Greenland ice cap crumbling into the ocean because of global warming somehow - indirectly and psychologically — be partly responsible for high oil and other commodity prices? The usual explanation ... focuses on explosive growth in emerging countries, China and India in particular... But psychology also matters in speculative markets, and perhaps that image of the Greenland ice disappearing makes it seem all too plausible that everything else- land, water, even fresh air - is running out too.

Let’s take a case study, the last generalised boom-bust cycle in commodity prices, which caused these prices generally to rise (more or less) from some time in the 1960’s until the 1980’s, and then generally to fall until the mid-1990’s. ...The conventional “fundamental” explanation for that cycle relates it to ...[t]he 1973-1974 oil crisis... [and the] 1979-1981 oil crisis... The drop in oil prices after the mid-1980’s is said to be due to the collapse of the OPEC oil cartel. But ... these events don’t really explain why prices of other commodities followed that of oil...

...Maybe more important than those wars in the 1970’s was that people throughout the world got worried about running out of things. This was the time of the “great population scare,” which transformed thinking worldwide, no doubt contributing to higher commodity prices while the fear lasted. There seemed to be some basis for this scare. The rate of increase in the world’s population rose from 1.8 per cent in 1951 to 2.1 per cent in 1971. But those were just dry statistics. Images likely mattered more...

...Today, we remain mostly unconcerned about global population growth. But, in the last ten years or so, we have become concerned about something else: rapid world economic growth. While it may seem that no image in the last decade was so dramatic as the first photo of the earth from space, think again...

...With so many vivid images of a shrinking and damaged planet, is it really any wonder that human psychology is ripe for high commodity prices?