Forecasts and reality can diverge dramatically but trends are much more stable. Forecasts for product prices and output can be spectacularly inaccurate if weather patterns change in a given year in an important crop producing region. They can also change if an important input such as oil or fertiliser spikes in price and significantly affects the price of inputs and the cost of production.
Producers in individual countries can also be dramatically affected by political decisions. Ethiopian farmers receive more for their grain than do their European counterparts and, over the last seven to eight years, we have seen an extraordinary convergence in dairy prices between New Zealand and Europe. Up to 2010, New Zealand dairy farmers had received about half the European price for milk – now they are, if not slightly above, Irish prices.