We examined the effects of temperature, ultraviolet-B (UVB) radiation and watering regime on aerobic methane (CH(4)) emission from six crops-faba bean, sunflower, pea, canola, barley and wheat. Plants were grown in controlled-environment growth chambers under two temperature regimes (24/20 and 30/26 degrees C), three levels of UVB radiation [0 (zero), 5 (ambient) and 10 (enhanced) kJ m(-2) d(-1)] and two watering regimes (well watered and water stressed). A gas chromatograph with a flame ionization detector was used to measure CH(4) emission rates [ng g(-1) dry weight (DW) h(-1)] from detached fresh leaves of each species and attached leaves of pea plants. Plant growth [stem height, leaf area (LA) and aboveground dry matter (AG biomass)] and gas exchange [net CO(2) assimilation (A(N)), transpiration (E) and water use efficiency (WUE)] were also determined. We found that higher temperature, water stress and UVB radiation at the zero and enhanced levels significantly enhanced CH(4) emissions. Crop species varied in CH(4) emission, which was highest for pea and lowest for barley. Higher temperature and water stress reduced all growth parameters, whereas ambient and enhanced UVB decreased stem height but increased LA and AG biomass. Higher temperature decreased A(N) and WUE but increased E, whereas water stress decreased A(N) but increased E and WUE. Zero and enhanced UVB reduced A(N) and E. Growth and gas exchange varied with species. Overall, CH(4) emission was negatively correlated with stem height and AG biomass. We conclude that CH(4) emissions may increase under climatic stress conditions and this extra source might contribute to the 'greenhouse effect'.