Dr. Hugh Cutcher
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Aerosol anomalies in 2025 reveal the outsized impact of Canadian wildfires on solar conditions, with smoke and particulates from one of the worst fire seasons in the country’s history driving major reductions in solar irradiance across Canada and beyond. While Canada saw a marked increase in aerosol loading, China and South America experienced anomalously low levels, supporting stronger irradiance conditions. Meanwhile, the Congo Basin registered worsening aerosol conditions, highlighting growing concerns for central Africa's solar outlook, according to analysis using the Solcast API. Aerosols impact solar irradiance by scattering and absorbing solar radiation as it passes through the atmosphere, when calculated this effect is called ‘aerosol extinction’.
Across Canada, 2025 aerosol extinction values were around 30% above climatological norms, indicating significantly higher levels of sunlight absorption and scattering by particulate matter. This spike is directly linked to the extreme wildfire season, with the total burned area in 2025 reaching twice the 10-year average. The timing of the peak fire activity, which aligned with the high-irradiance months of May and June, compounded the impact on solar conditions.
Smoke plumes from Canada were transported across the Atlantic by prevailing westerly winds, impacting solar production as far as Western Europe, where they overlapped with Spain's worst wildfire season in over a decade, further amplifying the regional aerosol burden.
Despite having a higher aerosol load than other solar generation regions, China experienced one of its cleanest atmospheric years in recent history. Aerosol extinction anomalies were approximately 20% below the recent climatology, driven by a combination of favourable meteorological patterns and continued reductions in industrial emissions. These conditions supported a strong irradiance performance throughout the past year when irradiance was already tracking 30% above average.
South America also recorded a notable improvement in aerosol conditions following a turbulent 2024. Anomalies in 2025 were generally 20% to 30% below average, allowing for clearer skies across the region. Solar production in Brazil, benefited from reduced smoke associated with a 45% reduction in burned areas within the Amazon Basin, as detected by the DETER satellite system. This significant decrease is part of a broader post-Bolsonaro shift in environmental management, further supported by La Niña-associated wetter conditions that helped suppress fire activity..
Meanwhile, the Congo Basin experienced worsening aerosol conditions, with extinction anomalies 20% to 30% above climatology. Unlike the declining trends in Saharan dust seen across northern Africa, this spike in aerosols is attributed to increasing fire activity within wet forest regions. The number of active fires in these forests has doubled over the past two decades, largely due to a combination of hotter, drier weather and anthropogenic factors such as conflict or agricultural-driven deforestation.
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