Variations and Inter Relationship in Mid-tropospheric Carbon Dioxide, Temperature and Water Vapour Using AIRS Observations

In the present study, trends and variations in carbon dioxide (CO₂), temperature and water vapour are analysed using 9 years (2003–2011) of mid-tropospheric (300–500 hPa) Atmospheric Infrared Sounder (AIRS) data. The focus of analysis remains on both a global as well as regional (India) scale along with improved understanding of their inter relationship. It was observed that the mid-tropospheric carbon dioxide increased from ~ 373 to ~ 393 ppm and ~ 373 to ~ 392 ppm, respectively, over the globe and the Indian region during 9 years. However, no substantial trends (increasing or decreasing) were observed in the temperature and water vapour observations for the same period of time. De-trended data of CO₂, temperature and water vapour were further analysed to understand the inter relationship between these parameters and the influence of two greenhouse gases (CO₂ and water vapour) on temperature. Analysis suggests a very high correlation (~ 0.90) between temperature and water vapour, however, no significant correlation was observed between temperature and carbon dioxide data, indicating that change in water vapour may have stronger influence on temperature compared to the change in CO₂, this feature can play a more significant role as a greenhouse gas than CO₂.