Comment on amt-2024-29

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The paper reviews and evaluates a 30-year-long atmospheric CO2 data series measured at Hegyhátsál tall-tower greenhouse gas monitoring site, a member of WMO GAW, NOAA, and ICOS networks (id. code: HUN). The paper also gives the technical description of the monitoring system, and that of the physical environment of the station. This low elevation (248 m above m.s.l.), mid-continental Central European site shows a 3.90±0.83 µmol mol -1 offset relative to the latitudinally representative marine boundary layer reference concentration presumably due to the European net anthropogenic emissions. The long-term trend (2.20 µmol mol -1 year -1 ) closely follows the global tendencies. In the concentration growth rate, the ENSO effect is clearly detectable with a 6-7 months lag-time. The summer diurnal concentration amplitude is slightly decreasing due to the faster-than-average increase of the nighttime concentrations, which is related to the warming climate. The warming climate also caused a 0.96±0.41 day year -1 advance in the beginning of the summer CO2-deficit season in the first half of the measurement period, which did not continue later. More than a century ago Ekholm (1901) and Arrhenius (1908) raised that carbon dioxide (CO2) produced by coal burning might accumulate in the atmosphere causing global climate change in the long run. Later, analyzing the sporadic measurements available, Callendar considered it proven that carbon dioxide was indeed accumulating in the atmosphere, and it might be the driver of the warming trend observed since the beginning of the 20th century (Callendar, 1938; 1949) . However, the measurements were not convincing due to their technical and representativeness problems. Finally, radiocarbon studies of Suess and Revelle confirmed that atmospheric carbon dioxide concentrations were indeed increasing (Suess, 1955; Revelle and Suess, 1957) , potentially foreshadowing dangerous global climate change. Their works led to the initiation of direct continuous monitoring of atmospheric carbon dioxide concentration by Keeling in 1957 (Keeling, 1960) . Since David Keeling's pioneering work, a large number of monitoring sites have been established around the world. In the beginning, they were established in very isolated remote places, far from any anthropogenic and biospheric influences (arctic regions, high mountain peaks, mid-oceanic islands). However, one of the main actors of the global carbon cycle is the biosphere with its climate-sensitive assimilation, respiration, and carbon storage. While the remote sites were able to record