The purpose of this study was to improve weed management systems under conditions of changing carbon dioxide concentrations and temperatures by evaluating the growth of Acalypha australis and Chenopodium album and observing the efficacy of four foliar and four soil herbicides as well as measuring phytotoxicity in soybean crops treated with these herbicides. In both growth chamber and greenhouse conditions, plant height and shoot fresh weight of Acalypha australis increased as temperature increased. However, in the case of Chenopodium album, plant height decreased as temperature increased, but shoot fresh weight was not significantly affected by higher or lower temperatures. There was no significant difference in germination rate of Acalypha australis and Chenopodium album under different carbon dioxide concentrations (400 or 800 ppm). However, ETR, plant height, leaf area, and shoot fresh weight of both weeds were higher at carbon dioxide concentrations of 800 ppm than 400 ppm. Efficacy of a foliar herbicide glufosinate on Acalypha australis was lower at 30℃ than at 20℃ and 25℃ in the growth chamber condition and was also lower at 29℃ than at 21℃ and 25℃ in greenhouse conditions. By contrast, efficacy of mecoprop on Acalypha australis was lower at 2 0℃ and 25℃ than at 30℃ in growth chamber conditions and lower at 21℃ and 25℃ than at 29℃ in greenhouse condition. In tests using foliar herbicide glyphosate, higher or lower temperatures did not produce lower herbicidal efficacy in growth chamber conditions, but herbicidal efficacy was lower at 21℃ than at 25℃ and 29℃ under greenhouse conditions. With soil herbicides, metolachlor and ethalfluraline efficacies were higher at relatively high temperatures under both growth chamber and greenhouse conditions. However, in the case of linuron, there was no difference in efficacy regardless of emperatures under both growth chamber and greenhouse conditions. Similar to tests with Acalypha australis, glufosinate efficacy on Chenopodium album decreased at higher temperatures under both growth chamber and greenhouse conditions. However, there was no difference in efficacy of glyphosate, mecoprop and bentazone on Chenopodium album regardless of temperatures. Soil herbicides metolachlor and linuron showed a decrease in efficacy at low emperatures under growth chamber and greenhouse conditions. The other soil herbicides alachlor and ethalfluralin showed no difference in efficacy regardless of the temperature conditions under growth chamber and greenhouse conditions. At standard application rates, carbon dioxide concentrations did not affect the efficacy of the four foliar herbicides in controlling Acalypha australis and Chenopodium album. However, when 1/2 and 1/4 of the recommended rates of glyphosate were applied to Acalypha australis and Chenopodium album, efficacy was lower under conditions of carbon dioxide concentrations at 800 ppm rather than at 400 ppm. When 1/4 of the recommended rate of bentazone was applied to Acalypha australis and Chenopodium album, efficacy was higher under conditions of carbon dioxide concentrations at 800 ppm than at 400 ppm. Regardless of the rates of application, glufosinate efficacy was not significantly different under conditions of different carbon dioxide concentrations. When applied at 1/4 of the recommended rate, the efficacy of ethalfuralin was higher under conditions of carbon dioxide concentrations of 800 ppm than 400 ppm. However, efficacies of other herbicides were not different regardless of carbon dioxide concentrations. Soybean phytotoxicity in crops treated with the recommended rate and two times the recommended rate of soil herbicides was not significantly different regardless of temperature and carbon dioxide concentrations. Overall, weed efficacy of some herbicides decreased in response to different temperatures and carbon dioxide concentrations. Therefore, new weed management methods are needed in order to ensure high rates of weed control in conditions affected by climate change.