Over the past four decades, global temperatures have increased more rapidly than before, potentially reducing vegetation activity if temperatures exceed the optimum temperature (Topt). However, plants have the capacity to acclimate to rising temperatures by adjusting Topt, thereby maintaining or even enhancing photosynthesis and carbon uptake. Despite this, it remains unclear how Topt of vegetation activity changes over time and to what extent global vegetation can acclimate to current temperature changes. In this study, we evaluated the temporal trends of Topt of vegetation activity and the thermal acclimation magnitudes globally using three remote-sensed vegetation indices and eddy-covariance observations of gross primary productivity from 1982 to 2020. We found that the global Topt of vegetation activity has increased at an average rate of 0.63 degrees C per decade over the past four decades. The increase in Topt closely tracked the rise in annual maximum daily mean temperature (Tmax), indicating that thermal acclimation has occurred widely across the globe. Globally, we found an average thermal acclimation magnitude of 0.38 degrees C per 1 degrees C increase in Tmax. Notably, polar and continental regions exhibited the highest thermal acclimation magnitudes, while arid areas showed the lowest. Additionally, the thermal acclimation magnitude was positively affected by interannual temperature variability and negatively affected by soil moisture and vapor pressure deficits. Our findings indicate that terrestrial ecosystems have acclimated to current climate warming trends with varying degrees, suggesting a greater potential for land carbon uptake. Moreover, these results highlight the necessity for earth system models to integrate the thermal acclimation of Topt to better forecast the global carbon cycle. Global warming affects vegetation growth, and plants may acclimate to temperature changes to enhance their growth and activity. However, how effectively global vegetation can adjust to temperature changes is unclear. To examine this, we analyzed satellite and ground data from 1982 to 2020 to determine changes in the optimum temperature of vegetation activity. We found that global vegetation has acclimated to rising temperatures by increasing the optimum temperatures. Polar and continental vegetation have undergone the greatest acclimation. In addition, ecosystems with humid climates and higher temperature variability have a greater capacity to acclimate to rising temperatures. These findings have important implications for better predicting how warming will affect the global carbon cycle. The optimum temperature (Topt) of global vegetation activity has increased rapidly, by 0.63 per decade over 1982-2020 The increase in Topt closely tracked the increase in air temperature, revealing widespread thermal acclimation across global vegetation Continental and polar ecosystems showed the greatest capacity for acclimation