The high latitude land (>50°N) is warming at more than twice the rate of the rest of globe. In spite of a broad consensus that the warming over the high latitudes northern forests (HLNF) has enhanced photosynthesis and contributed to the greening trend1,2, quantifying what the impact of temperature increase on photosynthesis and greenness has been difficult due to the concurring influence of the CO2 fertilization effect3. Here, using an ensemble of biogeochemical models from the Trends in Net Land Atmosphere Carbon Exchange project (TRENDY), we identified an emergent relationship between the spatial sensitivity of both gross primary productivity (GPP) and greenness (Leaf Area Index, LAI) to temperature and their corresponding temporal changes due to warming - the so-called carbon-climate feedback factor γ. Using spatially-resolved observations of GPP and LAI, we estimated the sensitivity of GPP and LAI increase due to temperature to be - 18.3 ± 2.6%/°C and 27.8 ± 4.3%/°C respectively. These observationally-derived sensitivities are ~50% and ~100% larger, respectively, than those diagnosed from the ensemble of TRENDY models. We estimated that the regional mean GPP increased 24 ± 3.7% between 2006-2015 and 1983-1992, much larger than the 5 ± 1.3 % increase from the CO2 fertilization effect implied by Wenzel et al.4. Taken together with the CO2 fertilization effect estimated by4, our results help resolve the partition of the competing effect between CO2 fertilization and warming on plants growth over the HLNF, and help reduce the uncertainties in predictions. Our results also highlight the dramatic changes of terrestrial biosphere caused by historical warming over the region. An important implication of this work is that uptake of carbon as temperatures continue to warm is likely to continue providing significant buffering of atmospheric CO2 increase