Why do meteorologists still debate whether cloud seeding is effective?

Meteorologists continue to debate the effectiveness of cloud seeding primarily because of the inherent complexity of atmospheric systems and the difficulty of conducting controlled scientific experiments.12

Key reasons for this ongoing debate include:

• Natural Variability: Precipitation is highly variable in space and time. Because clouds are complex, it is scientifically impossible to determine with certainty how much rain or snow would have fallen in the absence of seeding.1
• Experimental Limitations: Many early projects were commercial or private operations that lacked "randomized" control procedures, leading statisticians to reject their data as biased or inconclusive.1
• Inconsistent Outcomes: Evidence indicates that while ice-nuclei seeding can increase precipitation by some tens of percent under specific conditions, it can also lead to decreases of similar magnitude or have no effect at all in other situations.13
• Scale Constraints: Cloud seeding operates on the scale of individual clouds, making it impractical for large-scale weather modification. It cannot significantly alter the total water budget of a region or end droughts, as it requires the pre-existence of clouds to function.23