Abstract We present Li lidar observations in the mesopause region above Kühlungsborn, Germany (54°N, 12°E). The lithium layer is mainly formed by meteoric ablation. But lithium has a much higher relative abundance in space debris compared with meteoroids, making it a good indicator of anthropogenic influence in the upper mesosphere. Our measurements reveal a strong seasonal increase in Li abundance between August and December 2024, growing from ∼1.6×106 ${\sim} 1.6\times 1{0}^{6}$ to 4.7×106 $4.7\times 1{0}^{6}$ cm−2 ${\text{cm}}^{-2}$. These values are in reasonable agreement with the first simulations based on the Whole Atmosphere Community Climate Model (WACCM6) with a newly developed Li chemistry network; however, WACCM‐Li does not explain high Li abundances of up to 10.7×106 $10.7\times 1{0}^{6}$ cm−2 ${\text{cm}}^{-2}$ observed in January/February 2025. This may be due to anthropogenic effects or an unidentified natural mechanism. This study highlights the potential of lithium observations for monitoring the consequences of re‐entering space debris on the composition of the atmosphere.

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