Why in news?
A collaborative study by the Aryabhatta Research Institute of Observational Sciences (ARIES) and the Indian Institute of Astrophysics (IIA) has reported that water vapour heats the atmosphere more than aerosols over the Indo‑Gangetic Plains. Using satellite and ground‑based data, the researchers found that water vapour’s radiative effect is much stronger in clean skies and that aerosols modulate this effect when present. These findings are important for understanding how aerosols and moisture influence the monsoon and climate.
Background
Aerosols are tiny solid or liquid particles suspended in the air. They originate from natural sources such as dust, sea spray and volcanic eruptions, and from human activities like burning biomass, vehicles and industries. Aerosols can either scatter or absorb sunlight; they also provide surfaces for water vapour to condense, influencing cloud formation and precipitation. Water vapour is a greenhouse gas that absorbs and emits infrared radiation. The balance between aerosols and water vapour determines the atmosphere’s heating and cooling and thus affects regional climate and weather patterns.
Key findings of the study
- Dominant role of water vapour: The research shows that water vapour contributes far more to radiative heating than aerosols. When the atmosphere is free of aerosols, the heating effect of water vapour is very strong.
- Aerosol–water vapour interaction: In polluted skies, aerosols scatter sunlight and can cool the atmosphere near the surface. This moderates the heating effect of water vapour. The strength of the interaction varies by season and region.
- Implications for climate models: Many models treat aerosol and water vapour effects separately. The study suggests that their interaction must be incorporated to accurately predict monsoon onset and intensity.
- Indo‑Gangetic focus: The Indo‑Gangetic Plains experience heavy pollution and high humidity. The findings explain why thick haze can delay monsoon rainfall and why clear skies can trigger strong convection.
Significance
Understanding how aerosols and water vapour interact is critical for India’s climate forecasts and air quality policies. Clean‑air initiatives can amplify water vapour’s warming effect, potentially affecting rainfall patterns. Improved models can help authorities prepare for extreme weather and design strategies to reduce emissions without unintended climatic consequences.
Conclusion
The study emphasises that water vapour is a major driver of atmospheric heating in the Indo‑Gangetic region while aerosols can either dampen or enhance this effect. Policymakers and scientists need to treat aerosols and moisture as interconnected factors rather than independent variables when planning emission controls and analysing monsoon behaviour.
Source: PIB
