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Atmospheric rivers (ARs) are filamentary structures within the atmosphere that account for a substantial portion of poleward moisture transport and play an important role in Earth's hydroclimate. However, there is no one quantitative definition for what constitutes an atmospheric river, leading to uncertainty in quantifying how these systems respond to global change. This study seeks to better understand how different AR detection tools (ARDTs) respond to changes in climate states utilizing single‐forcing climate model experiments under the aegis of the Atmospheric River Tracking Method Intercomparison Project (ARTMIP). We compare a simulation with an early Holocene orbital configuration and another with CO2levels of the Last Glacial Maximum to a preindustrial control simulation to test how the ARDTs respond to changes in seasonality and mean climate state, respectively. We find good agreement among the algorithms in the AR response to the changing orbital configuration, with a poleward shift in AR frequency that tracks seasonal poleward shifts in atmospheric water vapor and zonal winds. In the low CO2simulation, the algorithms generally agree on the sign of AR changes, but there is substantial spread in their magnitude, indicating that mean‐state changes lead to larger uncertainty. This disagreement likely arises primarily from differences between algorithms in their thresholds for water vapor and its transport used for identifying ARs. These findings warrant caution in ARDT selection for paleoclimate and climate change studies in which there is a change to the mean climate state, as ARDT selection contributes substantial uncertainty in such cases. Atmospheric rivers are filaments of moisture in the atmosphere that play an important role in precipitation, but there is no one agreed‐upon method to define them. This study compares multiple definitions of atmospheric rivers in climate models that either change the timing and intensity of seasons by altering the orbit or make the planet colder by lowering CO2levels. We found that the various definitions of atmospheric rivers tended to agree in the model in which the seasons changed, but there was substantial disagreement in the model of the colder planet. The most likely reason for this is the definitions are based on modern‐day observations. While the climate for the model with the altered seasons was on average similar to the modern, the colder model was substantially different, particularly as it relates to the amount of water in the atmosphere. Atmospheric river detection tools are applied to climate model simulations incorporating insolation and greenhouse gas changesAR frequency changes due to orbital forcing and associated changing seasonality generally agree across algorithms in most regionsAR frequency changes due to lower greenhouse gas concentrations agree in sign, but there is substantial disagreement in magnitude Atmospheric river detection tools are applied to climate model simulations incorporating insolation and greenhouse gas changes AR frequency changes due to orbital forcing and associated changing seasonality generally agree across algorithms in most regions AR frequency changes due to lower greenhouse gas concentrations agree in sign, but there is substantial disagreement in magnitude