A study on the linkage between extreme temperature and atmospheric Carbon dioxide variability over India

Authors:

Smrati Gupta^1,2*, Yogesh K. Tiwari¹, J. V. Revadekar¹, Pramit Kumar Deb Burman¹, Supriyo Chakraborty¹, Palingamoorthy Gnanamoorthy^3,4

¹Indian Institute of Tropical Meteorology, Pune, Ministry of Earth Sciences, Govt. of India

²Institute of Environment and Sustainable Development, Banaras Hindu University, Varanasi, India

³Coastal Systems Research, M. S. Swaminathan Research Foundation, Chennai, India

⁴Key Laboratory of Tropical Forest Ecology, Chinese Academy of Sciences, Menglun, China

Abstract           

A significant amount of the major greenhouse gas, carbon dioxide (CO₂), released into the atmosphere is sequestered by the terrestrial biosphere. Climatic parameters such as temperature, precipitation, soil moisture, etc., modulate this sequestration capacity or sink in varied limits. A little information is available on the impact of extreme temperatures on the terrestrial biosphere sequestration of atmospheric CO₂. This study explores the modulation in the terrestrial sink of CO₂ caused by the frequently occurring extreme temperature phenomenon such as heatwaves over the Indian domain. Heatwaves are extreme temperature phenomena extending from the North-west Indian region towards the south-east region, occurring primarily in the pre-monsoon season of March-May (MAM), sometimes prolonged until June. The high intensity and duration of heatwaves during the season lead to the loss of human work capacity, health, economic losses, and even lives. The year 2015 witnessed one of the dreadful heatwave events in recent years, resulting in the loss of more than 2500 human lives within a season owing to heatwaves. The frequency and intensity of heatwaves are projected to increase further soon globally, including India, in the light of global climate change. It is not only of concern for human resources.

From the biosphere perspective, the terrestrial sink of CO₂ has also been studied to get affected by heatwaves. Temperature is one of the prime factors responsible for photosynthesis and ultimately for the available atmospheric CO₂ fixation by the plants. As such, the CO₂ fixation by the biosphere is affected during MAM season due to limited reduced soil moisture in this hot and dry season, leading to higher atmospheric CO₂ concentrations. In this study, we examine the sub-seasonal variability in the atmospheric CO₂ observed within MAM, driven by subdued fixation by ecosystems in the presence of extreme temperature phenomena like heatwaves. Here, available observations of CO₂ flux or Net Ecosystem Exchange (NEE) flux from MetFlux India Project funded by the Ministry of Earth Sciences, India, studied in conjunction with the retrieved atmospheric and columnar CO₂ concentrations from instruments aboard Atmospheric Infrared Sounder and Orbiting Carbon Observatory-2 satellites during the heatwave period of the year 2015. Our results suggest during a heatwave period, there is an initial increase in carbon uptake by the ecosystem with the temperature rise. But a further rise in temperature after some critical high temperature (~ 32 ͦ C) tends to reduce CO₂ uptake compared to the non-heatwave period of the same season. The satellite retrievals also noticed an increase in atmospheric CO₂ concentrations by 2-3 ppm during the heatwave period. The impact and feedback of heatwaves on the biospheric component of the carbon cycle is one of the significant outcomes of this study.