Aerosol–Water Vapour Interactions Are Critical to Accurate Climate Predictions: New Study

Aerosols and water vapour both play critical roles in regulating Earth’s climate by scattering and absorbing incoming solar radiation and outgoing terrestrial radiation.

New research has uncovered the combined and interconnected role of aerosols and water vapour in shaping regional climate dynamics, underscoring that reliable climate projections—particularly for the Indian summer monsoon—cannot be achieved by studying these components in isolation.

The study highlights that interactions between aerosols and water vapour significantly alter the Earth’s radiation balance, influencing atmospheric heating, surface temperatures, and large-scale circulation patterns. The findings carry major implications for climate prediction models, especially over South Asia’s Indo-Gangetic Plain (IGP)—one of the world’s most densely populated and aerosol-polluted regions.

Why Aerosols and Water Vapour Matter Together

Aerosols and water vapour both play critical roles in regulating Earth’s climate by scattering and absorbing incoming solar radiation and outgoing terrestrial radiation. While aerosols influence cooling or warming depending on their composition, water vapour is the most abundant greenhouse gas and a powerful driver of atmospheric heating.

Until now, their combined radiative effects have remained poorly constrained, contributing to uncertainties in regional climate projections. This study addresses that gap by quantifying how aerosol loading alters water vapour radiative effects (WVRE)—and vice versa.

Indo-Gangetic Plain: A Climate Hotspot with High Uncertainty

The Indo-Gangetic Plain is a global hotspot of aerosol loading, with strong seasonal and spatial variability in both aerosols and water vapour. This makes the region particularly challenging for climate models, despite its critical role in shaping monsoon circulation and rainfall patterns.

To improve understanding, researchers analysed long-term observations from six AERONET (Aerosol Robotic Network) sites across the IGP and conducted advanced radiative transfer simulations using the SBDART model.

Key Findings: Water Vapour Dominates Atmospheric Heating

The study found that:

• Water vapour contributes significantly more to atmospheric heating than aerosols, making it a dominant driver of regional climate over the IGP.

• The radiative effects of water vapour are strongly modulated by aerosol presence, revealing a complex and previously underappreciated interaction.

• In clean, aerosol-free atmospheres, water vapour radiative effects are much stronger at the surface and within the atmosphere.

• In aerosol-laden conditions, water vapour effects become more pronounced at the top of the atmosphere, altering the overall radiation budget.

• Solar position and aerosol absorption properties further influence these interactions, adding complexity to climate response patterns.

These results demonstrate that aerosol–water vapour coupling plays a decisive role in shaping regional climate outcomes, particularly in monsoon-sensitive regions.

Implications for Climate Models and Policy

The findings, published in the journal Atmospheric Research, suggest that climate models must explicitly incorporate aerosol–water vapour interactions to reduce uncertainty in projections of temperature, rainfall, and extreme weather events over South Asia.

“Water vapour heats the atmosphere far more efficiently than aerosols, but its impact is strongly shaped by aerosol loading. Ignoring this interaction risks underestimating key climate feedbacks,” the researchers noted.

A Collaborative Global Effort

The study was conducted by scientists from the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, and the Indian Institute of Astrophysics (IIA), Bengaluru, both autonomous institutes under the Department of Science and Technology (DST), Government of India, in collaboration with the University of Western Macedonia, Greece, and Soka University, Japan.

The research team was led by Dr. Umesh Chandra Dumka (ARIES) and Dr. Shantikumar S. Ningombam (IIA), with contributions from Dimitris G. Kaskaoutis, R.E.P. Sotiropoulou, E. Tagaris, and Dr. Pradeep Khatri.

A Call to Action for Climate Modellers and Policymakers

As India faces increasing climate risks—from heatwaves to erratic monsoon rainfall—the study sends a clear message to climate modellers, policymakers, and Earth system scientists: future climate assessments must move beyond isolated parameters and adopt integrated approaches that capture real atmospheric complexity.

Accurately representing aerosol–water vapour interactions could be key to improving monsoon forecasts, strengthening climate resilience strategies, and informing evidence-based policy decisions in one of the world’s most climate-vulnerable regions.