Climate Change and Climate Variability: Interconnections for Agriculture 1. Theoretical Considerations.

Much attention is currently devoted to the issue of climate change, defined as the long-term shift in the mean values of climatic parameters such as temperature, rainfall, etc. An equally important issue, especially in agriculture, is the fluctuation of climate parameters about their mean values, be those fluctuations random or in some sense systematic. An example of the latter is the recurrent phenomenon known as the El Niño-Southern Oscillation (ENSO). A vital question as yet insufficiently explored is the possibility that both the mean values of climatic phenomena and the patterns of their variation (over time and space) may be changing simultaneously due to anthropogenic forcing. We explore that possibility in theory, examine what data are available regarding possible changes in the frequency, intensity, and regional patterns of ENSO and other oscillations, and identify research questions relevant to linking such climate phenomena to agronomic production.