Yes, ‘Global Brightening’ Is Real. No, It Does Not Prove CO₂ Is a Climate Hoax.
Surface sunlight increased sharply across parts of Europe after air pollution declined. But the viral claim that this is ‘10 times larger than CO₂ forcing’ compares different physical quantities and misrepresents what the data show.
A climate claim spreading online begins with something scientists genuinely agree on: parts of Europe became brighter after the dirty-air era of the 1960s and 1970s.
From the mid-20th century into the 1980s, industrial regions experienced ‘global dimming’: less solar radiation reached the ground because aerosol pollution scattered and absorbed sunlight and altered cloud properties. Then sulfur emissions and other pollutants fell sharply across much of Europe. The atmosphere became cleaner and more sunlight reached the surface. Scientists call the recovery ‘global brightening.’
Potsdam in Germany has one of the world’s longest radiation records. Research using data from 1947 to 2017 found multidecadal surface-solar-radiation swings on the order of 10 W/m². Other European stations show substantial changes too. So the basic observation is real: air pollution once reduced sunlight, and cleaner air allowed part of that sunlight back.
The viral argument goes wrong when it says this proves sunlight, not CO₂, is driving modern warming because the brightening number is supposedly ten times larger than CO₂ forcing.
Those numbers are not directly comparable.
A station measuring an extra 10 or 15 W/m² at the surface is measuring a local or regional shortwave energy flux under that location’s cloud and aerosol conditions. CO₂ radiative forcing is normally expressed as a globally averaged change in Earth’s energy balance after accounting for radiation entering and leaving the climate system. NOAA estimates CO₂’s effective forcing at roughly 2.33 W/m² in 2024 relative to preindustrial conditions.
Putting Potsdam’s local surface change beside a global top-of-atmosphere forcing and dividing one by the other is physically misleading. They are measured in the same unit but describe different parts of the climate system at different spatial scales.
There is another problem: brightening is not uniform worldwide. A recent global assessment found an average brightening of about 0.88 W/m² per decade from 1984 to 2018, stronger over land than oceans, with some regions dimming instead. Aerosol reductions were especially important over Europe, while cloud changes mattered strongly at global scale.
The irony is that global brightening is itself evidence of human influence. The Potsdam study concluded that aerosol pollution was likely a major driver of the dimming-brightening cycle. Humans dirtied the atmosphere enough to reduce incoming sunlight, then cleaned much of that pollution up. The climate responded in both directions.
This also helps explain why some 20th-century greenhouse warming was temporarily masked. Sulfur aerosols cool the climate by reflecting sunlight. When Europe and North America reduced those pollutants, some of that cooling mask disappeared. Cleaner air therefore brought major health benefits while also revealing more of the warming influence from long-lived greenhouse gases.
Aerosols and CO₂ also behave differently in time. Aerosol pollution is short-lived: stop emitting it and much of the atmospheric effect disappears rapidly. CO₂ accumulates and influences the climate system for centuries through the carbon cycle. A regional brightening episode can be a large short-term surface-energy change without replacing the long-term global greenhouse forcing.
The better scientific question is not ‘sunlight or CO₂?’ Climate responds to multiple forcings at once: greenhouse gases, aerosols, clouds, volcanic eruptions, solar variability, land use and ocean circulation.
Global brightening is real. It matters for heat, agriculture, solar power and regional climate. But using a local sunlight increase to declare CO₂ irrelevant requires an apples-to-oranges comparison that the underlying papers do not support.
The interesting conclusion is actually more complicated than either side’s slogan: cleaner air has contributed to warming in some regions by removing a human-made cooling influence, while rising greenhouse gases continue adding a long-lived warming influence globally. Both can be true at the same time.