India is slowly losing its sunshine. A new study by Indian scientists has found that the number of sunshine hours across the country has been falling steadily over the past three decades, and pollution is to blame.

The study, conducted by researchers from Banaras Hindu University, Indian Institute of Tropical Meteorology (IITM), Pune, and the India Meteorological Department (IMD), analysed sunshine data from 1988 to 2018. It was published in the journal Nature on October 2.

Sunshine hours declining across India

The scientists studied monthly sunshine hours (SSH) from 20 weather stations and nine regions. They found that the annual sunshine hours have continuously declined across most parts of India.

The study said there was a “persistent decline of SSH in the Indian subcontinent on all temporal scales, excluding the north eastern region, where mild seasonal levelling off was found.”

It also found that from October to May, sunshine hours slightly increased in most regions, but there were sharp drops from June to July, especially in areas other than the northern inland and Himalayan regions.

Pollution and aerosols behind ‘solar dimming’

Scientists say the decline in sunshine is caused mainly by aerosols, tiny particles released into the air from pollution, dust, and smoke. These aerosols block sunlight from reaching the ground.

According to the study, during the 1990s, “India’s economic growth drove urbanisation, land-use changes, and industrialisation, leading to increased fossil fuel consumption, vehicular emissions, and biomass burning.”

As a result, the number of aerosols in the atmosphere rose sharply, reducing solar radiation and sunlight.

How other countries fought the same problem

India wasn’t alone. Countries like China and Japan also saw rising aerosol levels in the early 1990s. But unlike India, they acted quickly to control the pollution.

China launched the Clean Air Action Plan, while Japan pushed clean technologies and emission control policies, which led to a “brightening trend”, meaning they regained sunlight hours.

India, however, did not take similar timely steps, the researchers said.

The study also points to increasing cloud cover as another reason for fewer sunshine hours. Aerosols are known to affect how clouds form and how long they last.

“As per the theory of condensation for warm cloud systems, bigger cloud droplets are formed when the natural balance of aerosols and humidity persists, and formation of perceptible clouds is achieved,” the study explained.

But when aerosol levels rise, “a greater number of smaller-sized cloud droplets are developed and the cloud lifetime is prolonged.” This means clouds stay longer in the sky, blocking sunlight for extended hours.

The findings show that India’s growing pollution and urbanisation are literally taking away its sunlight, a worrying sign for a country that depends heavily on solar energy. Without clear skies, not only is solar power generation affected, but it may also impact weather patterns and daily life in the long run.