Persistent wildfires in Canada create cross-continental solar drag

Smoke from ongoing Canadian wildfires has continued to suppress irradiance levels across Canada and the Eastern US into June, with impacts stretching as far as Europe. Persistent fire activity combined with stronger-than-usual westerly winds drove smoke haze across the Atlantic, causing measurable declines in solar irradiance on both sides of the ocean.

In Canada and the Eastern United States, early June saw more of the degraded irradiance and air quality observed in May. Solcast data shows clear sky irradiance (irradiance without cloud impacts) has been reduced by as much as 10% in affected areas compared to conditions last year, as wildfire aerosols scatter and absorb incoming sunlight.

Daily solar generation impacts of the smoke varied from city to city, and day to day, as the intensity increased and waned. Analysis of long-term average and actual irradiance from early June shows the heaviest impacts hit Minneapolis on June 1 and Toronto on June 6. Solar assets across all the North Eastern US, and Eastern Canada will have experienced similar impacts, suppressing solar energy availability in a swathe of high-capacity solar regions, from Alberta to the Midwestern U.S.

The surface-level impacts have been especially acute in population centers such as Ottawa, Montreal, and Toronto, where air quality warnings were issued during the first week of June. Further south and west, cities including Minneapolis have seen intermittent air quality alerts triggered by daily weather patterns drawing in wildfire smoke. These aerosol-laden skies have not only reduced direct irradiance but will be accelerating soiling on solar panels, compounding generation losses by decreasing panel efficiency between cleaning cycles.

The resulting scale of emissions has created a smoke plume large enough to traverse the Atlantic. By mid-May, satellite observations and Solcast irradiance data confirmed that Canadian wildfire smoke had reached Europe. Transatlantic transport has been facilitated by a pronounced belt of strong westerly winds in the upper atmosphere, running north of a persistent high-pressure anomaly. This flow pattern has enabled fine smoke aerosols to travel thousands of kilometers, bringing hazy skies and air quality alerts to parts of Western Europe on June 11 and 12.

Irradiance levels in these regions were slightly lower than in comparable periods from 2024, though both years exhibited haze-related suppression. While the 2025 reductions align closely with clear-sky expectations for this year, the presence of Canadian wildfire smoke likely contributed to the modest dip below modeled irradiance. In contrast, similar conditions last year may have been driven by Saharan dust, as the atmospheric loading of aerosols reduced the amount of solar energy reaching the surface.

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