The ecosystem carbon turnover time (τ) is an emergent ecosystem property that partly determines the feedback between the terrestrial carbon cycle and climate which is strongly controlled by temperature1–3. However, it remains uncertain to what extent hydrometeorological conditions may influence the apparent temperature sensitivity of τ, defined as the change in the carbon turnover times with a 10ºC rise in temperature (Q10). Here, we show that Q10 is unlikely temperature dependent and that it converges to 1.6 ± 0.1 globally once hydrometeorological conditions are taken into account. By investigating the responses of τ to temperature and hydrometeorological factors using an ensemble of observation-based global datasets and a global compilation of in-situ measurements, we show that temperature and hydrometeorology are almost equally important in shaping the spatial pattern of τ, explaining 60% and 40% of its global variability, respectively. Our findings reveal a strong constraint on Q10 values with significant reduction in magnitude and uncertainties, by accounting for the hydrometeorological effects on spatial variability of τ. These findings suggest that hydrometeorological conditions modulate the apparent temperature sensitivity of terrestrial carbon turnover times, confounding the role of temperature in quantifying the response of carbon cycle to climate change.