Changes in productivity could go both ways, less intensive upwelling in the areas where this occurs would adversely affect the productivity in these areas. This is what occurs during the famous El Nino events when warm waters are carried towards the west coast of South America and the upwelling diminishes, adversely affecting the anchovy stocks in the area and the fisheries of Peru and Chile (see Appendix). Conversely, the blooming of plankton could increase and so could the intensity of currents carrying plankton to certain areas, this is what happened in the warm period in the 1920s and 1930s in the northeast Atlantic, to be further discussed below. How fish stocks will be affected is a more complicated issue, depending on predator-prey interactions. As to the industry and society, changes in productivity of fish stocks may necessitate investment in new equipment or finding new markets, or cause obsolescence of real and human capital and loss of markets.