Trends in night temperatures, ozone concentrations and acid rain are presented. We tested the hypothesis that flowering in the cooler part of day or night could make plants much less vulnerable to high temperature induced sterility. We screened 96 cultivars originating from a range of latitudes and altitudes for the time-of-day when flowering commenced (TDF); no systematic relationship was observed. There was a 3 hour difference in TDF between the cultivars, the earliest being 0800 h. We also screened 87 wild rice accessions for TDF. The earliest was 0500 h and the latest was 2230 h. For the worst climate change scenario (6°C increase in average temperature), the predicted changes in crop duration, respiration and sterility, would reduce the yield of existing cultivars by 89%; yields for accessions with the earliest TDF would decline by 47%. For a temperature increase of 2°C, the predicted yield of existing cultivars would fall by 25%; those with the earliest TDF would fall by only 11%. The model predicted in the absence of climate change, differences in weather between El Niño and La Niña years would decrease yields by 22%; the greatest improvements in germplasm and management would increase farmers yield by 18%.