Surface solar radiation is the amount of the Sun’s energy that actually arrives at the ground after passing through the atmosphere. It is shaped by everything that stands in the way: clouds, water vapor, aerosols and the gases that generate them. Since the mid-twentieth century, researchers worldwide have documented a widespread dimming of SSR from roughly the 1950s through the 1980s, followed by a partial recovery, or brightening, in many regions. China, with its extraordinary industrialization and equally extraordinary clean-up efforts, has become one of the most important natural laboratories for understanding these swings. Yet long-term regional studies have been hampered by sparse observations, inhomogeneous records and the difficulty of separating the influence of clouds from that of pollution.

The new research, led by Anna Li of Sun Yat-sen University together with colleagues including Martin Wild of ETH Zurich, a leading authority on dimming and brightening, tackles these obstacles head-on. The team worked with a homogenized and reconstructed SSR dataset known as SSRIH20CR, which extends consistently back to the mid-twentieth century across China and its subregions. Homogenization is critical here: raw station records of radiation are riddled with artificial jumps caused by instrument changes, station relocations and calibration shifts. By correcting these artifacts and reconstructing missing periods, the dataset allows genuine climatic signals to emerge from the noise of measurement history.

With a trustworthy record in hand, the researchers turned to attribution, the hardest part of the problem. They combined two complementary statistical approaches: partial least squares regression, a linear technique that handles the strong correlations among pollutant emissions, and a random forest model, a machine-learning method capable of capturing nonlinear relationships between radiation and its potential drivers. Using both perspectives matters, because the relationship between an emission and the sunlight at the surface is rarely a simple straight line. Aerosols scatter and absorb light directly, but they also alter cloud properties, seeding more numerous smaller droplets that make clouds brighter and longer-lived, and even suppressing cloud formation through soot-induced heating of the atmosphere.

The headline result is a decisive verdict against clouds as the driver of long-term change. Total cloud cover, the team found, correlates well with the year-to-year variability of SSR, which is exactly what one would expect: a cloudier year is a dimmer year. But when it comes to the multi-decadal trend, cloud cover accounts for only about 4.1 percent of the variation. In other words, clouds explain the weather of the radiation record but not its climate. The slow, decades-long evolution of sunlight over China was written by something else entirely, and that something was pollution.

Among the aerosols and their gaseous precursors, three species stand out. Organic carbon, black carbon and sulfur dioxide contributed 24.7 percent, 22.3 percent and 13.7 percent respectively to the national variability of SSR. Organic carbon, largely a product of biomass and fossil fuel combustion, scatters sunlight efficiently. Black carbon, the sooty component of smoke, absorbs it, warming the atmosphere and modifying clouds. Sulfur dioxide, emitted mainly by coal burning, transforms in the atmosphere into sulfate particles, which are powerful scatterers. Together these three pollutants dominate the decadal fluctuations of radiation over China as a whole, and their fingerprints are strongest in the country’s densely populated and heavily industrialized eastern regions, where they collectively account for 49.8 percent of the variability.

The picture changes subtly as one moves west. In China’s western regions, the dominant drivers are ammonia, black carbon and organic carbon, which together contribute 53 percent of the variability. The prominence of ammonia, a gas released largely by agriculture, points to the importance of ammonium-containing particles formed when ammonia reacts with acidic species in the atmosphere. This east-west contrast is a reminder that China’s atmospheric chemistry is not monolithic: industrial coal combustion writes the radiation history of the eastern seaboard, while agriculture and combustion together shape the skies of the interior. Any national policy aimed at managing sunlight, whether for solar energy or for climate purposes, must therefore be tailored regionally.

Two other findings sharpen the story. First, total column water vapor, the total amount of water in the atmospheric column, contributes less than 5 percent to the long-term variation of SSR over China, a nearly negligible role compared with the aerosols. Second, the authors are careful to flag the limits of their method: because statistical attribution cannot fully disentangle physically entangled processes, the estimated contributions represent relative importance rather than strict physical attribution. That honesty matters, because aerosol-cloud interactions remain among the largest uncertainties in climate science, and no statistical model can fully replace a mechanistic simulation. Still, the convergence of linear and nonlinear methods on the same answer lends considerable weight to the conclusion.

The implications ripple outward in several directions. For the solar energy industry, the study confirms estimates that air pollution has cost China substantial photovoltaic production over the decades, and that the clean air actions launched in 2013 have effectively been a solar energy subsidy, brightening the skies over the country’s eastern power markets. For climate science, the work reinforces the view that reductions in scattering and absorbing aerosols, while unambiguously beneficial for human health, unmask additional greenhouse warming by removing a veil that has been dimming the surface. China’s experience suggests that as other developing regions industrialize and then clean up, they will trace a similar arc from dimming to brightening, with radiation trends tracking their emissions of organic carbon, black carbon and sulfur dioxide far more closely than any change in the clouds above.

Subject of Research: Long-term variations and drivers of surface solar radiation over China

Article Title: Evolution and drivers of surface solar radiation over China since the mid-twentieth century

Article References: Li, A., Li, Z., Zhang, H., Jiao, B., Wei, S., Wild, M., & Li, Q. (2026). Evolution and drivers of surface solar radiation over China since the mid-twentieth century. Climate Dynamics, 64(10), Article 414. https://doi.org/10.1007/s00382-026-08318-6

Image Credits: AI Generated

DOI: 10.1007/s00382-026-08318-6

Keywords: surface solar radiation, global dimming and brightening, aerosols, black carbon, organic carbon, sulfur dioxide, cloud cover, air pollution, China, climate dynamics, random forest, attribution

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