India is losing sunshine.
A new study by six Indian scientists finds that over the past three decades, daylight hours – the time during which direct sunlight reaches the Earth’s surface – have steadily declined across most of India, due to clouds, aerosols and local weather conditions.
Data from 20 weather stations from 1988 to 2018 show a persistent decline in daylight hours nationwide, with only the northeast region experiencing a slight seasonal respite, according to the paper published in Scientific Reports, a peer-reviewed journal published by Nature Portfolio.
Scientists from Banaras Hindu University, the Indian Institute of Tropical Meteorology and the Indian Meteorological Department report that the steepest annual declines have occurred in the northern interior region – notably Amritsar and Calcutta – as well as along the Himalayan belt and the west coast, particularly in Mumbai.
All nine geographically diverse regions of India recorded an overall annual decline in sunshine hours, although the rate of decline varied across India. The monthly analysis revealed significant increases from October to May, followed by sharp declines from June to July in six of nine regions.
This seasonal trend in sunshine intersects with a deeper, long-standing problem: the severe air pollution crisis in India – now among the world’s 10 most polluted countries – which scientists trace back to the 1990s. Rapid urbanization, industrial growth and land-use changes have led to increases in fossil fuel use, vehicle emissions and biomass burning, sending aerosols in the atmosphere and attenuating the sun’s rays.
Daylight hours in Mumbai gradually decreasing, scientists say [Getty Images]
In winter, heavy air pollution from smog, temperature inversions, and crop burning in the Indo-Gangetic plains produces light-scattering aerosols, reducing daylight hours.
These aerosols – tiny solid or liquid particles from dust, vehicle exhaust, crop fires and other sources – persist in the air long enough to affect sunlight, climate and health.
From June to July, monsoon clouds cover much of India, significantly reducing sunlight, although aerosol levels are lower than in winter.
Scientists note that higher hours of sunlight from October to May do not indicate cleaner air; rather, they reflect more cloudless days. Hazy winter sunlight can scatter or diffuse, reducing intensity without completely blocking the sun, which instruments still record as daylight hours.
“Our study found that the decrease in daylight hours is linked to clouds that persist longer without releasing rain, thereby blocking more sunlight. These clouds that last longer are formed indirectly because of aerosols that change the weather and climate,” says Manoj Kumar Srivastava, professor of geophysics at Banaras Hindu University and one of the study’s authors.
Aerosols have reduced the amount of sunlight reaching the ground in India by about 13%, while clouds have contributed to an additional 31% to 44% decline in surface solar radiation between 1993 and 2022, according to Sachchida Nand Tripathi, an atmospheric scientist at the Indian Institute of Technology (IIT) Kanpur.
These trends raise concerns for agriculture, daily life and India’s solar energy ambitions, while highlighting areas where solar panels could be most effective.
Solar energy now accounts for 47% of India’s renewable energy capacity. The government says it is on track to reach 500 GW of renewable energy by 2030, with more than 100 GW of solar installed by early 2025. But declining sunshine could cast a shadow over the country’s solar ambitions.
According to Professor Tripathi, air pollution is making the problem worse. It reduces solar panel production by 12 to 41 percent depending on the type of photovoltaic system — the technology that converts sunlight into electricity — and costs an estimated $245 million to $835 million in lost electricity production.
India’s solar ambitions could be dampened by declining sunlight [LightRocket via Getty Images]
Studies also show that cleaner air could increase India’s annual solar energy production by 6 to 28 terawatt hours of electricity, enough to power millions of homes for a year.
But the impact of pollution doesn’t stop at solar energy. It also takes a heavy toll on agriculture, leading to an estimated 36-50% loss in crop yields – mainly rice and wheat – in the most polluted parts of the country, according to Professor Tripathi.
India is not the only one losing sunshine; Across the world, increasing air pollution and changing weather patterns have darkened the skies.
A study published in Atmospheric Chemistry and Physics observed that Europe likely experienced a reduction in sunlight reaching the ground due to air pollution between 1970 and 2009. In Germany, daylight hours decreased by about 11% between 1951 and 1980, due to industrial gas emissions and associated cloud formation.
Research has also shown that stricter air quality laws in the 1990s led to increased hours of sunshine across Europe.
China also experienced a significant decline in sunlight hours between the 1960s and 2000s, mainly due to increased aerosol emissions from rapid industrialization. Sunshine duration varied across Chinese cities, with some areas experiencing greater declines due to factors such as air pollution.
The good news: Scientists say Earth’s surface has been gradually receiving more sunlight since the 1980s — a trend known as global brightening, after decades of decline.
A new analysis of satellite data from 1984 to 2018 appears to confirm this, showing that the effect is strongest over land and in the Northern Hemisphere, mainly due to the decline in aerosols in the 1980s and 1990s and changes in cloud patterns.
The bad news: highly polluted countries like India are being left behind. If the Sun continues to hide behind smog, India risks running on steam instead of operating at full power.
