Current-minus-future spring slopes had negative estimates in four England Meadow Brown samples in 1976-2023

We tested whether current spring temperature slopes of Meadow Brown mean flight dates were more negative than next-spring slopes. We used 17,263 site-year records in northern and southern England in 1976-1999 and 2000-2023. Joint models controlled site effects and linear time. Current-minus-future slopes ranged from -5.60 to -1.58 days per C. Three of four adjusted intervals included zero. Only early South had an interval below zero; that interval included zero with equal total year weights. All planned sensitivity estimates and all single-year omission estimates stayed negative. The test did not establish a clear repeated timing-specific link across the four samples. Future weather is an imperfect diagnostic for shared trends and omitted conditions. Selected sites, common weather, short annual series, coarse grids and missing visit histories limit inference. This test does not identify a causal climate effect or an air pollution effect. The package includes source hashes, code, exact model inputs, all fits and offline checks.

phenology · butterflies · spring temperature · future exposure · negative control · observation bias · temporal specificity