Water vapour heats Earth's atmosphere more than aerosols from industry, volcanoes: Study

Water vapour contributes far more to heating the Earth's atmosphere than aerosols released from industrial activity and volcanic eruptions, according to a new study conducted by Indian and international scientists.

The research highlights the combined role of aerosols and water vapour in shaping climate change impacts, stressing that both must be considered together for reliable climate assessments and future projections. Their interaction, the study notes, can significantly influence regional atmospheric behaviour, including the Indian summer monsoon.

Radiative effects of aerosols and water vapour are critical to understanding the Earth's radiation balance and overall climate dynamics. These effects determine how incoming solar radiation and outgoing terrestrial radiation are scattered or absorbed, directly affecting global temperatures, weather systems and climate stability.

The Indo-Gangetic Plain (IGP) is regarded as a global hotspot for aerosol concentration, marked by high spatial and temporal variability in both aerosols and water vapour. This complexity makes it particularly difficult to accurately quantify their climatic impacts.

The study was carried out by the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, and the Indian Institute of Astrophysics (IIA), Bengaluru - both autonomous institutions under the Department of Science and Technology - along with international collaborators from the University of Western Macedonia in Greece and Soka University in Japan.

The research team assessed how water vapour's radiative forcing depends on aerosol loading over the Indo-Gangetic Plain. Scientists analysed data from six AERONET (Aerosol Robotic Network) stations across the region and conducted radiative transfer simulations using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model.

The team was led by Dr Umesh Chandra Dumka of ARIES and Dr Shantikumar S Ningombam of IIA, with contributions from Dimitris G Kaskaoutis, R E P Sotiropoulou and E Tagaris of the University of Western Macedonia, and Dr Pradeep Khatri of Soka University.

Their findings, published in the journal Atmospheric Research, show that water vapour has a significantly greater impact on atmospheric heating than aerosols across the densely populated and highly polluted Indo-Gangetic region.

The study also found that the radiative effects of water vapour are strongly influenced by aerosol presence. When aerosol concentrations are low, water vapour's heating effect is stronger near the Earth's surface and within the atmosphere. However, in more polluted conditions, the impact of water vapour becomes more pronounced at the top of the atmosphere, underscoring a complex interaction between the two.

According to the researchers, water vapour's dominant role in atmospheric heating amplifies its importance in influencing regional climate over the Indo-Gangetic Plains.

The results further reveal that these effects depend heavily on solar position and atmospheric factors related to aerosol absorption, showcasing the combined influence of aerosols and water vapour in shaping climate outcomes.