Evidence for global warming is inferred from the onset of earlier flowering times in plants from the Washington, DC, area. First-flowering times over a 29 year period were examined for 100 plant species representing 43 families of angiosperms. The trend of average first-flowering times for all plants/year for 100 species shows a significant decrease of -2.4 days over the 29-year period. When 11 species that exhibited later first-flowering times were excluded from the data set, the remaining 89 showed a significant decrease of -4.5 days. Trends for earlier-flowering species ranged from -0.2 to -46 days, while those for later-flowering species ranged from +0.3 to +10.4 days. Onset of earlier flowering in these 89 species is inversely correlated with local changes in minimum temperature (TMIN). Our results are concordant with other studies where warmer air temperatures and higher CO2 levels have lead to advancement of the average annual growing season.

Key words: climate change, earlier plant flowering, global warming, growing season