We analyzed gross primary productivity (GPP), total ecosystem respiration (TER), and resulting net ecosystem exchange (NEE) of carbon dioxide (CO₂) by the terrestrial biosphere during the summer of 2018 through the monitoring network (ICOS – Integrated Carbon Observation System), and using inverse modeling and remote sensing. Reductions in productivity highly correlated but independently derived from solar-induced fluorescence, near-infrared vegetative reflectance, and GPP simulated by the Simple Biosphere model version 4 (SiB4) suggest a GPP reduction of 130-340 TgC in July-August-September of 2018. This occurs over an area of 1.6 × 106 km² with anomalous low precipitation values in northwestern and central Europe. In this drought-affected area, the reduction of GPP, TER, NEE and soil moisture at ICOS ecosystem sites are satisfactorily reproduced by the SiB4 model. We found that, unlike the previous 5 years, low soil moisture is the main stressor in the affected area. The SiB4 NEE reduction of 57 TgC for JAS coincides with anomalous atmospheric CO2 observations in 2018, and this is closely related to the NEE anomaly derived from CarbonTracker Europe (52 to 83 TgC). The increase in NEE during the spring (May–June) 2018 (SiB4 −52 TgC; CTE −46 to −55 TgC) largely compensated for this loss, as ecosystems took advantage of favorable growing conditions. This article is included in the theme ‘Impacts of the severe drought and heatwave in 2018 in Europe: from site to continental scale.’