Climatological Assessment of GHGs in Greece from over Two Decades of CAMS Atmospheric Composition Data (2003–2024)

This study analyzes climatological trends and variability of the main greenhouse gases (GHGs)—carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO)—over Greece using Copernicus Atmosphere Monitoring Service (CAMS) data (EAC4 and EGG4) alongside global emission inventories and satellite-derived fluxes. A statistically significant positive long-term trend was identified for both CO2 and CH4. CO2 concentrations have been increased by approximately 2 ppm/year, reaching over 415 ppm in 2020 compared to 380 ppm in 2003, following the global trends of ground-based measurements in the northern hemisphere. CH4 showed a rapid increase since 2007, linked to anthropogenic activities, although natural sources also contribute. In contrast, CO exhibits a negative trend of about 0.6 ppb/year, with significant seasonal variability due to both anthropogenic sources and wildfires. Notably, CO concentrations increased during wildfire episodes in 2021 and 2023, with enhanced CO concentrations over 100 ± 20 ppb, well above typical summer values of 80 ± 10 ppb. Both CO2 and CH4 exhibit positive seasonal anomalies relative to the 2003–2013 reference period. Analysis of short- and mid-term variability reveals that CO2 fluctuates within ±0.5%, with higher winter concentrations linked to anthropogenic emissions, while CH4 variability reaches ±2%, reflecting diverse urban, industrial, and agricultural sources. CO exhibits the highest variability (±10–50%) due to its shorter atmospheric lifetime and sensitivity to local emissions and wildfire events. Sectoral comparisons with the Greek National Inventory Report indicate a general decline in GHG emissions in Greece, although sector-specific differences persist. Seasonal patterns show elevated fossil CO2 emissions during colder months, CH4 emissions peaking in agricultural seasons, and CO peaks during summer wildfires. In general, CAMS GHG emission trends fall well within the National Inventory Report of Greece. These findings emphasize the importance of combining long-term trends with short- and mid-term variability to capture both anthropogenic and natural influences on GHGs, providing a more comprehensive understanding of emission dynamics in Greece, when global warming and climate change remain an inherently challenging issue during the last decades.