Climate change poses a serious threat to the sustainability and productivity of plantation crops in tropical and subtropical regions. In India, tea (Camellia sinensis (L.) O. Kuntze), a major plantation crop and economic driver, is particularly sensitive to changing climatic variables. This study analyzes the shifts in critical climatic variables across four major Indian tea-growing regions, viz., South Bank (Assam), Nagrakata (West Bengal), Anamallais (Tamil Nadu), and the High Ranges (Kerala) over a 30-year period (1996–2025). Using the Mann–Kendall trend test and Sen’s slope estimator, significant spatiotemporal climate variations like maximum and minimum temperatures (Tmax, Tmin), rainfall (RF), and relative humidity (RH) were analyzed. Data were segregated into demi-decadal and seasonal intervals to observe periodic and seasonal fluctuations. Findings showed that the South Bank and Nagrakata regions experienced a significant increase in Tmax (p < 0.001), with a rise of 1.1 °C−1.3 °C compared to long-term averages, while Tmin decreased significantly (p < 0.001) by 1.8 °C in South Bank. In the case of Nagrakata, although long-term RF increased (p < 0.05), total rainfall notably decreased by 88 mm in 2025, while in South Bank, the decrease was 364 mm. The morning and afternoon RH in both regions declined (p < 0.05), where the afternoon RH dropped by about 2%. In Anamallais, Tmax declined (τ-coefficient = −0.07), while winter Tmin increased. Notably, overall seasonal RF significantly increased (p < 0.05), alongside a significant rise in morning and afternoon RH (p < 0.001). Conversely, the High Range regions showed a widening temperature gap, with Tmin rising significantly (p < 0.001) in recent years. While overall seasonal rainfall increased (p < 0.05), the critical monsoon rainfall decreased, along with its morning RH (p < 0.05). These changing trends of the overall climatic pattern have a substantial impact on tea cultivation and its production. In order to safeguard this tea sector, the study discusses the urgent implementation of integrated adaptation and mitigation strategies, including the deployment of drought-tolerant cultivars, agroforestry for microclimate regulation, and multi-scalar policy frameworks to protect the millions of livelihoods tied to this labor-intensive industry.