This study examined global atmospheric variations in carbon dioxide (CO2) and methane (CH4), which are two major greenhouse gases (GHGs). The main objectives were as follows: (1) identify the top 50 cities with the highest long-term (2003-2020) mean annual CO2 and CH4 mixing ratios (kg/kg) at 1000 hPA, (2) analyze 18year trends in mixing ratios for cities worldwide, (3) conduct a spatiotemporal analysis of column-averaged CO2 and CH4 concentrations, and CO2 and CH4 mixing ratios at 1000 hPa from 2003 to 2020, and (4) assess the impact of GHG emissions on near-surface air temperature (NSAT). These objectives were achieved using the Copernicus Atmosphere Monitoring Service (CAMS) global greenhouse gas reanalysis product and the ERA5 reanalysis dataset. The findings indicated that Chengdu (China) had the highest long-term mean annual CO2 mixing ratio, followed by Luoyang (China), Chongqing (China), Myitkyina (Myanmar), Louangphrabang (Laos), Lampang (Thailand), Louang Namtha (Laos), Aizawl (India), Nola (Central African Republic), and Los Angeles (USA). Katowice (Poland) exhibited the highest long-term mean annual CH4 mixing ratio, followed by Sao Paulo (Brazil), Lahore (Pakistan), Delhi (India), New Delhi (India), Moscow (Russia), Chengdu (China), Anshan (China), Andijan (Uzbekistan), and Fergana (Uzbekistan). Between 2003 and 2020, the mean annual columnaveraged CO2 concentration increased from approximately 372-379 ppm to 409-418 ppm, whereas the column-averaged CH4 concentration increased from about 1599-1861 ppb to 1711-2016 ppb. The global average CO2 and CH4 concentrations (weighted by the cosine of latitude) increased from nearly 375 ppm to 412 ppm and from 1735 ppb to 1837 ppb, respectively, during 2003-2020. The global average NSAT (weighted by the cosine of latitude) also increased from 14.36 degrees C to 14.80 degrees C between 2003 and 2020, showing an increase of 0.44 degrees C. This comprehensive analysis highlights the urgent need to address GHG emissions to mitigate their environmental and climatic effects.