Heralded for more than a decade
, climate change
may seem no surprise. But just as some unexpected
happening is no surprise while its specific quality is,
so it is with climate change. A debate over supersonic
airplanes projected cooling to have a dire impact.
Observations of rising 
brought dire projection
of warming
and drying. When the American breadbasket
turned dry in 1988, the warmer, drier climate
seemed at hand. But during 1993, floods in the Amer
ican heartland discredit or at least discount predictions
made only five years before. Computer simulations,
of course, had disagreed all along whether rising
would make North America drier or wetter.
So unsure of what it actually may be, I place climate
change among surprises.
In the short run before adaptation, most climate change will lower yields. Even in the long run, if cropland in temperate climates grows hot or dry, yields will fall and land may be taken from Nature for crops. On the other hand, if cropland too cold warms and that too dry moistens, yields will rise, saving other land for Nature. Conflicting and changing projections and experience mean that farmers can only diversify portfolios (Council for Agricultural Science and Technology, 1992[fAST92]) and await the surprises.