A novel thought experiment utilizing state-of-the-art climate model simulations has revealed how and when unequivocal signals of human-caused climate change could have been first detected since the 19th century. By assuming early availability of troposphere and stratosphere temperature monitoring and validating model accuracy with observed climate variability, researchers established that increases in atmospheric CO2 and associated warming have long surpassed natural variability. This study underscores the importance of ongoing climate observations for understanding anthropogenic impact and bolsters historical climate science foundations inspired by early pioneers like Syukuro Manabe.