Main objectives

The project entitled “Fire-emitted Pollution and Climate change: linkages in the past, present, and future” (FirePC) aimed to advance understanding of the role of wildfires in the Earth system by investigating their effects on atmospheric composition, the radiation budget, and climate. Specifically, the project aimed to:

• Thoroughly evaluate the ability of state-of-the-art Earth System Models (ESMs) to reproduce the impact of wildfire emissions on atmospheric composition at the global scale, with emphasis on aerosols, ozone, and their precursor species.
• Quantify the effective radiative forcing (ERF) associated with wildfires, from the pre-industrial period to the present day.
• Systematically investigate the impacts of wildfire emissions on present-day and future climate, at both global and regional scales.

Beyond these scientific objectives, FirePC aimed to develop expertise in modelling wildfire-climate interactions, train early-career researchers, and strengthen Greece’s position in this emerging research field.

Key activities

The project was organised into five Work Packages (WPs 1–5) described below. An integrated modelling framework was employed, combining the EC-Earth3, UKESM, NorESM and CESM2 ESMs; the global chemical transport model TM5-MP; the high-resolution regional model WRF-Chem; and the fire models JULES-INFERNO and INFERNO-peat. These models incorporate wildfire emissions and simulate their impacts on atmospheric chemistry and the atmospheric energy budget.

• WP1 – Model evaluation, impacts of wildfire emission variability, and improvement of wildfire representation: EC-Earth3 and TM5-MP were evaluated against a broad range of ground-based (AERONET) and satellite observations, including MODIS, MOPITT, GOME-2 and OMI, using the GFED4s and GFED5 biomass-burning emission datasets. The influence of interannual variability in wildfire emissions on tropospheric composition was investigated using the two emission datasets. In parallel, the INFERNO-peat fire model was developed and improved using experimental data from eight different peatland environments.
• WP2 – Impacts of wildfires on present-day climate: Simulations with EC-Earth3 and WRF-Chem were conducted to investigate the impacts of present-day wildfires at global and regional scales through case studies of the August 2021 wildfires in Greece, the unprecedented Canadian wildfires of 2023 and 2025, and the South American wildfires of 2024.
• WP3 – Pre-industrial to present-day wildfire emissions Effective Radiative Forcing (ERF): ERF of the present-day wildfire emissions compared to pre-industrial times was determined using four ESMs (EC-Earth3, CESM2, NorESM and UKESM).
• WP4 – Present-day and future climate responses to wildfire emissions: Climate responses to wildfire emissions were investigated using EC-Earth3, CESM2 and UKESM, while future changes in fire activity were assessed with JULES-INFERNO under different Shared Socioeconomic Pathways (SSPs).
• WP5 – Project management and dissemination: WP5 covered the overall management of the project and dissemination of its results through scientific publications, presentations at national and international conferences, and the organisation of the FirePC dissemination event.

Results

Model evaluation and improvement and impacts of wildfire interannual variability on tropospheric composition (WP1): The systematic comparison of EC-Earth3 and TM5-MP with ground-based and satellite observations demonstrated the ability of the models to reproduce the response of atmospheric composition to wildfire emissions. The influence of interannual variability in wildfire biomass-burning emissions was analysed with TM5-MP over 1997–2015, a period encompassing major global wildfire events and different phases of ENSO (El Niño–Southern Oscillation). The analysis demonstrated that the sensitivity of interannual variability (IAV) in tropospheric composition to variability in biomass-burning emissions differs substantially among chemical species: it is strong and global in extent for CO, more regionally confined for aerosol optical depth and NO₂, and weak for O₃. The resulting variability in atmospheric composition shows spatial coherence and seasonal consistency with known major wildfire events and El Niño phases. This finding has direct implications for how the temporal variability of wildfire emissions should be represented in chemical transport models and ESMs.

In parallel, the development of INFERNO-peat, based on experimental data from eight peatland environments, improved the ability to predict peat-fire risk and its climatic impacts.

Atmospheric and climate impacts of extreme wildfire events (WP2): EC-Earth3 simulations of the unprecedented 2023 Canadian wildfires revealed widespread impacts across the Northern Hemisphere, including increased aerosol loading, perturbations to the radiation budget, surface cooling, increased cloud cover, reduced precipitation, and changes in atmospheric circulation. Two complementary studies investigated the remote impacts of the same wildfire event. The first showed that smoke from the Canadian wildfires caused cooling and circulation changes that partially weakened the Indian summer monsoon mechanism during the exceptionally dry August 2023 period. Comparison with radiosonde measurements, satellite observations and reanalysis data supported the proposed mechanism. The second study estimated that the reduction in incoming solar radiation caused by the smoke resulted in an approximately 2.8% reduction in photovoltaic energy generation across North America and Europe during May–September 2023, with associated additional CO₂ emissions and economic losses approaching USD 2 billion.

The analysis was extended to the 2025 Canadian wildfires as part of the State of Wildfires 2025–26 report, with similar findings of widespread cooling, increased cloud cover and reduced precipitation over eastern North America and the North Atlantic. In contrast, the analysis of the 2024 South American wildfires revealed local warming, reduced cloud cover and an intensification of the dry season, indicating potential positive wildfire–climate feedbacks across the region. At the regional scale, WRF-Chem simulations of the extreme wildfire event in Greece in August 2021 showed that the effects of wildfire aerosols are not confined to directly affected areas: while cooling occurs in the source regions, meteorological feedbacks can result in warming in neighbouring areas.

Across all these studies, comparison with ground-based and satellite observations demonstrated that including wildfire emissions substantially improves the representation of aerosols and atmospheric composition, directly contributing to the first objective of the project.

Pre-industrial to present-day wildfire emissions ERF (WP3): Simulations with four ESMs (EC-Earth3, CESM2, NorESM, and UKESM) showed that the ERF caused by wildfire emissions from the pre-industrial times to the present is driven primarily by aerosol-cloud interactions and, to a lesser extent, by changes in surface albedo and climate feedbacks, such as changes in atmospheric water vapour. At the same time, the intercomparison of the four models revealed substantial spread in the ERF estimates, while showing good agreement in the regions experiencing the strongest impacts. The use of four models contributed to reducing uncertainty in the ERF associated with wildfire emissions, thereby fulfilling the second main objective of the project.

Present-day and future climate response to wildfire emissions (WP4): EC-Earth3 simulations under present-day conditions showed that wildfires cause global-scale cooling and substantial changes in precipitation, particularly in the tropics. Simulations with CESM2, UKESM and EC-Earth3 under future SSP scenarios indicated that wildfire emissions are likely to be underestimated in these scenarios because they do not account for climate-change feedbacks on wildfire activity. Even with improved emission estimates, substantial differences remain among models in their estimates of the climatic effects of wildfires, making the overall wildfire impact one of the major sources of uncertainty in Earth system modelling. Finally, JULES-INFERNO simulations showed an overall increase in burned area across Greece under all examined SSP scenarios, with southern Greece remaining particularly vulnerable. These findings fulfil the third objective of the project.

All results and objectives were achieved and, in several cases, exceeded. The main areas exceeding the original plan were: (a) the inclusion of an additional ESM in the ERF analysis under WP3, and (b) the extension of the analysis to extreme wildfire events under WP2 (Greece 2021, Canada 2023 and 2025, and South America 2024). Although these activities were not included in the original plan, they substantially enhanced the scientific and societal relevance of the project.

Impact

Scientific impact: FirePC contributed to bridging the fields of atmospheric chemistry, aerosol physics and climate science by integrating Earth System Models, atmospheric chemistry models, high-resolution regional models, fire models, and satellite and ground-based observations within a common evaluation framework. The main areas of added value are:

• First systematic comparison of four ESMs for the ERF of wildfire emissions. This comparison reduced uncertainty in the ERF estimates, demonstrated that aerosol–cloud interactions are the dominant mechanism across all four models, and provides a reference framework for future international model assessments.
• Demonstration of atmospheric composition impacts of wildfire emissions variability. Interannual variability in wildfires translates into interannual variability in biomass burning emissions. This produces strong, globally extensive variability in tropospheric CO; variability confined to regional scales in aerosol optical depth and tropospheric NO₂ and weak variability in tropospheric O₃. The variability patterns are spatially and temporally coherent with major fire events and with El Niño phases.  CO and NO₂ affect air quality and are ozone precursors, while tropospheric O₃ acts both as a pollutant and as a short-lived climate forcer.
• Identification of the role of organic aerosols. The results showed that cloud changes driven by wildfire emissions are primarily associated with organic aerosols rather than black carbon, with direct implications for the parameterisation of aerosol–cloud interactions in ESMs.
• Improvement of the JULES-INFERNO fire model through the development of INFERNO-peat, which represents peatland fires at high latitudes and can be incorporated into future versions of ESMs.
• Evidence for an underestimation of future wildfire emissions in current climate-change scenarios due to the lack of climate-change feedbacks on wildfire activity itself, with direct implications for future climate projections.
• A new methodological capability – the use of ESMs to investigate the atmospheric impacts of individual extreme wildfire events. FirePC demonstrated that such events can alter atmospheric composition, cloud cover, atmospheric circulation and the radiation budget not only locally but also at hemispheric scales, adding to the growing body of evidence that major wildfires are an active driver of short-term climate variability.

The results for the 2023 and 2025 Canadian wildfires suggest that the repeated occurrence of extreme wildfires at high latitudes may become an increasingly important climate forcing, with potential impacts on both local weather and longer-term climate variability over the North Atlantic.

Societal and economic impact: By linking wildfire emissions to impacts on the Indian summer monsoon and photovoltaic energy production, FirePC highlighted the socioeconomic consequences of extreme wildfires and how these can manifest thousands of kilometres from their source. The results can be used by policymakers, meteorological and climate services, as well as the energy, agricultural and water-management sectors, supporting the development of early-warning services and risk-assessment tools. For Greece in particular, the projected increase in burned area under all SSP scenarios, with southern Greece remaining particularly vulnerable, provides directly relevant information for national wildfire prevention and adaptation planning. In parallel, dissemination activities contributed to raising public awareness of the impacts of wildfires on climate and air quality.

Human capacity and research infrastructure: FirePC trained early-career researchers in Earth system modelling, analysis of satellite and ground-based observations, and the use of high-performance computing systems through their active participation in the international EC-Earth and TM5-MP modelling communities. The project promoted open science through the publication of datasets in open repositories (Zenodo). Finally, the successful execution of computationally demanding simulations on national (GRNET/ARIS) and institutional supercomputing infrastructures demonstrated Greece’s capacity to participate effectively in international climate-change research.

Future impact: The results of FirePC are directly relevant to modelling communities and international initiatives such as FireMIP, AerChemMIP and CMIP, contributing to the continued improvement of Earth system models. INFERNO-peat and the multi-model ERF comparison framework are expected to support future model evaluation activities, while the five papers currently under preparation or review will further extend the scientific impact of the project beyond its completion. The new research collaborations established through the project provide a basis for continuing research into wildfire-climate interactions and further strengthening the international visibility of the Greek research community.