Past, current, and future solar radiation trends in Europe

  • Published on Nov 28, 2025
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Authors:
Leandro C. Segado-Moreno, José A. Ruiz-Arias, Juan Pedro Montávez, Juraj Betak

Published in Remote Sensing of Environment, volume 333

3 November 2025

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Overview

For the past several decades, Europe has experienced a "brightening" trend, a measured increase in the long term average of the solar radiation reaching the ground (Surface solar radiation - SSR). This phenomenon has significant implications for the regional climate system, the global energy budget, and the operational performance of photovoltaic energy systems.

A recent paper, "Past, current and future solar radiation trends in Europe: Multi-source assessment of the role of clouds and aerosols", conducted by researchers from the Universities of Murcia and Málaga in collaboration with our Solargis experts, provides a comprehensive assessment of this trend. The study quantifies the magnitude of historical brightening, attributes its causes by decoupling the effects of aerosols and clouds, and projects future SSR trends through 2054.

Methodology

The study employed a multi-source approach to create a robust characterization of SSR trends across time and space. The analysis integrated three primary data types:

  1. Ground Observations: Data from a network of 46 quality-checked and homogenized ground stations (from the GEBA/WRDC archives) provided reliable, high-precision point measurements. The used ground observations passed stringent quality assurance checks to exclude inhomogeneous site data, which would otherwise lead to incorrect observed trends.

  2. Gridded Datasets: Five historical datasets, including four satellite-based models (Solargis-3.2, SARAH-3, CLARA-A3, CEBAF-4.2.1) and the ERA5 reanalysis, were used to analyze temporal and, chiefly, spatial patterns, thanks to their coverage of almost the whole continent. To ensure temporal stability of the gridded data, it was compared to the ground observations, and bias and root mean square deviation were quantified. The Solargis dataset was benchmarked and found to be a top performer.

  3. Climate Projections: An ensemble of 30 CMIP6 climate models, involving nearly 300 climate change projections, was used to analyze historical simulations (1994-2014) and project future trends (2024-2054) under four different forcing scenarios (SSP1-2.6 to SSP5-8.5).

Main findings

Historical Trend (1994-2023)

The analysis confirms a positive SSR trend across Europe, observed in all studied datasets. Based on the ground-station network, the regional trend observed from 1994 to 2023 was +3.1 W/m2 per decade, with the Solargis-3.2 and SARAH-3 datasets exhibiting trends within ±0.2 W/m2 per decade compared to the ground observations. Compared to the overall daily SSR mean value for that period in Europe (143 W/m2), SSR has increased, on average, 2.2 % per decade. The brightening was spatially widespread, with the most pronounced increases occurring in Central Europe, particularly northeastern France, the Benelux countries, and western Germany.

Trend Attribution

A primary achievement of the study is the quantitative attribution of this trend. By using model simulations to isolate the aerosol direct effect, and neglecting the potential contribution of water vapor trends, the researchers partitioned the drivers of brightening:

  • ~20% Aerosol Direct Effect (ADE): This portion of the trend is attributed to reductions in atmospheric aerosols (pollution). Cleaner air directly allows more sunlight to penetrate the atmosphere.

  • ~80% Cloud-Related Effects: The majority of the trend is linked to changes in clouds. This component was further subdivided:

    • ~40% First Aerosol Indirect Effect (AIE): Reductions in aerosols also mean fewer particles to act as cloud condensation nuclei. This makes clouds less reflective, allowing more radiation to pass through.

    • ~40% Thermal Effect (TE): Rising air temperatures, associated with global warming, were found to contribute to a decrease in overall cloud coverage, further enhancing the amount of SSR reaching the surface.

Conclusions and future projections

The observed brightening in Europe is a complex phenomenon driven in roughly equal parts by the aerosol indirect effect, the thermal effect on cloud cover, and to a lesser extent, the aerosol direct effect.

The CMIP6 climate models project that this strong trend will not continue as the median projected SSR trend for 2024-2054 is approximately 85% smaller than the trend observed from 1994-2023. This stabilization is projected to occur regardless of the future emissions scenario. The models suggest this is due to opposing trends in more severe scenarios: a decrease in clear-sky radiation (a dimming effect) is counterbalanced by an increase in cloudy-sky radiation (a brightening effect from cloud suppression). However, this result must be interpreted cautiously since climate models showed important limitations when their predictions were compared to actual observations during 1994-2014.

The study also notes that the CMIP6 ensemble, while useful for projections, tended to underestimate the observed historical trend and overestimate the relative importance of the clear-sky (ADE) trend compared to the cloud-related trends.

Further reading