Aerosols and Clouds Have Halved Surface Warming Over India, Study Finds

India is no stranger to heat. As the most populous country on Earth and one of its hottest, the subcontinent endures punishing spring and summer heatwaves that only relent when the monsoon arrives. Yet amid the relentless march of global climate change, scientists have noticed something puzzling: India, along with surrounding regions of the tropics, is warming more slowly than nearly any other major landmass on the planet. A new observational study now offers a detailed explanation for this so-called cooling paradox, pointing to an unexpected alliance between atmospheric particles and clouds that has quietly shielded the surface from roughly half of the warming it would otherwise have experienced.

The research, conducted by a team at Vikram Sarabhai Space Centre in Thiruvananthapuram, India, examined satellite and ground-based observations spanning 2001 to 2024. The findings, published in the journal Ocean-Land-Atmosphere Research, quantify for the first time how aerosols — tiny solid and liquid particles suspended in the atmosphere — and cloud cover have combined to weaken the surface warming trend over the Indian region. According to the analysis, surface dimming caused by these factors produced a cooling effect of about 0.125 degrees Celsius per decade, a magnitude almost identical to the observed warming trend of 0.138 degrees Celsius per decade. In other words, without this dimming, the region would have warmed at nearly twice the rate recorded in recent decades.

Aerosols come from many sources. Some are natural, such as dust lifted from arid landscapes, ash from volcanic eruptions, or smoke from wildfires. Others are man-made, generated by manufacturing, power generation, and the exhaust of vehicles crowding India’s rapidly growing cities. Whatever their origin, these particles share a common climatic property: they intercept and scatter incoming sunlight before it can reach the ground. The result is a dimming of the surface beneath them, a shading effect that suppresses local temperatures even as greenhouse gases continue to trap heat in the atmosphere overall.

While satellite data has long confirmed that elevated aerosol concentrations and increased cloud cover reduce surface temperatures in affected areas, this effect had not been rigorously quantified over India across the past three decades. Vijayakumar S. Nair, a scientist in the Space Physics Laboratory at Vikram Sarabhai Space Centre and lead author of the study, explained that the observed cooling paradox over the region has been linked primarily to increased aerosol loading and the lower climate sensitivity of the region. The goal of the new work, he noted, was to quantify the contributions of aerosols and clouds to the reduced warming trend using both satellite and ground-based observations.

The study’s findings carry particular weight because India sits at the intersection of two competing environmental pressures. On one hand, the country’s industrialization and urbanization have filled its skies with anthropogenic aerosols, contributing to some of the world’s worst air quality. On the other, the region’s dense population makes it acutely vulnerable to extreme heat, which threatens agriculture, water supplies, and public health. Understanding precisely how atmospheric particles have moderated surface warming is therefore not merely an academic exercise; it has direct implications for how climate change will unfold for more than a billion people.

One of the more striking discoveries of the research is that the composition of aerosols over India has changed over time. Although the total aerosol loading has increased, the shifting mixture of particle types has actually reduced the cooling potential of the aerosols present. This means that the protective dimming effect is not static: as the chemical and physical character of the particles evolves, their ability to shade the surface may weaken, potentially allowing the full force of greenhouse-driven warming to emerge more clearly in the years ahead.

The study also teased apart the relative roles of aerosols and clouds, and the results are instructive. Cloud cover, it turns out, contributed twice the cooling capacity of aerosols, delivering a surface cooling of about 0.08 degrees Celsius per decade compared with roughly 0.04 degrees Celsius per decade from the aerosols themselves. Together, these two mechanisms explain a substantial portion — though not all — of the diminished surface warming experienced in and around India over the past three decades. The remainder likely reflects other regional factors, including the lower climate sensitivity that characterizes tropical land areas.

The implications for future climate projections are significant. Nair emphasized that the large uncertainty in aerosol-cloud interactions, combined with the lower climate sensitivity of the tropics, poses a major challenge for scientists attempting to forecast surface temperature trends. The problem becomes especially acute when considering air quality policies: many measures designed to reduce aerosol pollution for public health reasons will, as a side effect, strip away the very particles that have been masking warming. Cleaner air could paradoxically unmask a sharper rise in temperatures, a trade-off that policymakers will need to confront as India works to improve its air while preparing for a hotter future.

Reducing the uncertainties associated with aerosol-cloud interactions is, according to Nair, the next priority for the research community. Because these interactions operate at small spatial scales and involve complex physics — particles acting as cloud condensation nuclei, altering cloud brightness, lifetime, and rainfall — they remain among the most stubborn sources of uncertainty in climate models. Continued observational efforts, combining satellite instruments such as the Moderate Resolution Imaging Spectroradiometer aboard NASA’s Aqua and Terra satellites with long-term ground measurements, will be essential to tracking how aerosol loading and composition evolve and how the delicate balance between dimming and warming shifts over time.

The research team included Anas Ibnu Basheer of the Space Physics Laboratory at Vikram Sarabhai Space Centre and the Faculty of Marine Science at Cochin University of Science and Technology, along with Akhila RS, Prijith SS, Mukunda M Gogoi, and S Suresh Babu, all of the Space Physics Laboratory. The study received no specific funding, and the authors declared no conflicts of interest. As the world continues to warm, the Indian experience serves as a vivid reminder that the climate story is not written by greenhouse gases alone: the particles and clouds overhead are quietly shaping how that warming is felt on the ground, and understanding their role may prove critical to anticipating what comes next.

Subject of Research: The role of atmospheric aerosols and clouds in reducing surface warming over India

Article Title: Atmospheric particles slow global warming over India

Article References: Atmospheric particles slow global warming over India. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: aerosols, India, climate change, surface dimming, cloud cover, warming trend, heatwaves, satellite observations, air quality, tropics, climate projections, Vikram Sarabhai Space Centre