Long-term atmospheric CO₂ observations are essential for understanding changes in the global carbon cycle and assessing the impacts of anthropogenic emissions on climate. The importance of such records was first demonstrated by the Keeling Curve, the continuous CO₂ measurements initiated at Mauna Loa Observatory in 1958, which revealed a persistent rise in atmospheric CO₂ along with distinct seasonal variability.

A continuous record of atmospheric CO₂ measurements has been maintained at the Shadnagar monitoring station since 2013, resembling the CO₂ Keeling curve. Figure 1 depicts more than decadal high-frequency in-situ CO₂ observations from July 2013 to January 2026 using ground-based instrument to investigate atmospheric CO₂ variability over Shadnagar, a semi-urban region near Hyderabad, India indicating increasing trend of about 2.8 ppm yr-1. These measurements were calibrated with CO₂ reference cylinders supplied by the National Oceanic and Atmospheric Administration (NOAA) as recommended by the World Meteorological Organization (WMO).

Fig.1 Long-term variability of atmospheric in-situ CO₂ at suburban (NRSC-ISRO) site of India

Figure 2a shows the monthly CO₂ growth rate derived, reflecting inter-annual fluctuations rather than long-term behaviour. In contrast, the trend-based growth rate provides a more robust estimate of the underlying increase, yielding a mean growth rate of 2.82 ppm yr⁻¹. This value is consistent with global atmospheric CO₂ growth rates, indicating that the observed increase is largely driven by large-scale anthropogenic forcing, with regional modulation. Figure 2b illustrates the mean seasonal cycle of atmospheric CO₂ along with its amplitude. The seasonal cycle exhibits pronounced amplitude of 12.68 ± 2.08 ppm, indicating strong biospheric control over CO₂ variability in the region.

Fig. 2a and 2b Annual growth rate (slope) and Seasonal cycle of atmospheric CO₂

Hence, the long-term measurements of GHGs are essential and are key drivers for understanding the climate change induced by atmospheric composition. Further, this will aid in evolving policies at the national level to mitigate GHG emissions as per SDG-13 by 2030 while meeting the international agreements at the Conference of Parties.