Global warming driven by rising fossil fuel emissions and land use and land cover change has led to an increase in the frequency and intensity of climate extremes. While terrestrial photosynthetic uptake is expected to increase with rising atmospheric carbon dioxide (CO₂) due to CO₂ fertilization, the increase in ecosystem respiration fluxes with elevated temperature will likely cause a reduction in total net biospheric production (NBP). Climate extremes, such as heatwaves and droughts, are expected to increase over time and potentially impact terrestrial carbon uptake. However, uncertainty in the characteristics of extremes in NBP and their climate drivers is high. We identified NBP extremes in a climate change simulation of the Community Earth System Model (CESM2) from 1850 through 2100. We found that the magnitude and the rate of increase of negative NBP extremes are larger than for positive extremes. About 88% of regions are dominated by negative NBP extremes towards the end of the 21^st century. The single most dominant climate driver is soil moisture anomaly. The compound effect of hot, dry, and fire cause 50% of all NBP extremes. While the temperature sensitivity to NBP is positive in high latitudes, the correlation between NBP anomalies and temperature anomalies during extremes changes from positive to negative over time. The increase of frequency and magnitude of net negative NBP extremes and decline in total terrestrial NBP indicate an accelerated weakening of terrestrial carbon uptake until and potentially beyond the 21^st century.