Information on the impact of climate change on the growth of weed species and their sensitivity to herbicides could help to establish an efficient weed management strategy. Due to the excessive use of acetolactate synthase (ALS)-inhibitor herbicides, resistance to those herbicides is increasing globally. It is, thus, crucial to find out whether the efficacy of these herbicides will change in the future due to the increase in temperatures and carbon dioxide concentration. Therefore, this work aimed to evaluate the impact of temperature and carbon dioxide (CO2) changes on the growth of Amaranthus retroflexus, Bromus tectorum, Chenopodium album, and Echinochloa crus-galli, including the assessment of sulfosulfuron 75% + metsulfuron methyl 5% efficacy in these weeds. A factorial experiment was performed in a completely randomized design with a factorial arrangement (2 × 2 × 6), including two CO2 concentrations (400 and 700 ppm), two temperature regimes (30/20 °C and 34/24 °C day/night), and six herbicide rates (0, 25, 37.5, 50, 62.5, and 75 g ha−1). As a result, it was seen that temperature and CO2 concentration changes influenced the morphological variables of the weeds. The temperature regime affected the herbicide’s effectiveness on B. tectorum and E. crus-galli. The herbicide’s efficacy on weed species was affected by the interaction of herbicide rates and the temperature regime, except for on E. crus-galli; the highest efficacy was observed at 30/20 °C and at a rate 50% higher (75 g ha−1) than the recommended one (50 g ha−1). Except for E. crus-galli, increasing CO2 concentrations enhanced the herbicide efficacy and ALS enzyme activity inhibition in all the weed species, but had the greatest effect on C3 weeds. We found that temperature and CO2 levels can alter the efficacy of weed control with herbicides, with clear differences between C3 and C4 plants. As a result, increased temperature and CO2 concentration will possibly allow better control of weed species such as B. tectorum, C. album and A. retroflexus at lower doses of the ALS herbicide under investigation.