In the vast tapestry of human-driven environmental change, cropland expansion stands as one of the most transformative alterations to the Earth’s surface since the dawn of industrialization. While the impacts of such land-use change on carbon emissions and deforestation have been widely studied, new research is now shedding light on a subtler, yet equally significant atmospheric consequence—how the spread of agriculture diminishes natural aerosol production and alters the Earth’s radiative balance. A groundbreaking study employing advanced Earth system modeling reveals that cropland expansion has led to a measurable decrease in biogenic secondary organic aerosols (SOA), which in turn weakens a natural cooling effect on the planet’s climate system.
Secondary organic aerosols are minute particles formed in the atmosphere through the oxidation of volatile organic compounds released primarily by plants and trees. These biogenic aerosols play a critical role in scattering sunlight and enhancing cloud droplet formation, both processes that help to cool the Earth’s surface by reflecting solar radiation back to space and increasing cloud albedo. Until now, the climate models assessing radiative forcing effects from land-use change largely overlooked the influence of cropland expansion on these aerosols, instead focusing predominantly on carbon fluxes and anthropogenic pollutant emissions.
In a sophisticated series of sensitivity experiments, researchers integrated state-of-the-art SOA processes into a comprehensive Earth system model, explicitly incorporating mechanisms like organic new particle formation. Their simulations contrasting preindustrial and present-day land cover unequivocally demonstrate an approximate 10% reduction in the global burden of biogenic SOA attributable to the conversion of forests into croplands since the industrial era began. This reduction is largely driven by the replacement of evergreen and deciduous broadleaf forests, which emit substantial quantities of biogenic volatile organic compounds (BVOCs), with croplands that emit comparatively little.
The implications of this decreased aerosol burden are profound. Because biogenic SOA contribute to scattering incoming sunlight and act as cloud condensation nuclei (CCN) that enhance cloud brightness and longevity, the observed reduction leads to a diminished radiative cooling effect. Quantitatively, the study estimates this decline in SOA radiative forcing at 146 ± 112 mW m⁻², a figure that amounts to roughly 8% of the total radiative warming forcing caused by accumulated CO₂ emissions since industrialization. This magnitude is sufficiently large to warrant serious attention in the broader context of climate change feedbacks.
Crucially, the study extends its analysis into future climatic scenarios. Under projected warming, along with anticipated decreases in anthropogenic aerosol and precursor gas emissions due to pollution control measures, the radiative impacts of cropland-induced decreases in biogenic SOA are expected to intensify by about 50%. This amplification arises from anticipated shifts in biogenic emission intensities, where elevated temperatures could alter vegetation-driven emissions of volatile organic compounds, and from changes in the ambient concentration of background CCN, further influencing cloud microphysics and aerosol-cloud interactions.
The findings challenge prevailing assumptions in climate science and policy frameworks by highlighting a previously underappreciated pathway through which land-use changes interact with atmospheric chemistry and physics. Whereas mitigation strategies often prioritize reducing greenhouse gas emissions and controlling industrial aerosol pollution, land-use decisions that expand cropland at the expense of forests inadvertently suppress a natural cooling mechanism, exacerbating warming trends.
The substitution of rich, high-BVOC-emitting forests with croplands fundamentally alters the atmospheric composition and aerosol lifecycle. Forests, with their dense canopy and diverse species, release a plethora of organic compounds that undergo oxidation to form SOA. These particles not only scatter sunlight but also serve as CCN, stimulating cloud formation, especially of low-level clouds that have significant albedo effects. Croplands, on the other hand, emit far less BVOCs and consequently generate fewer SOA particles, diminishing the atmosphere’s natural reflective capacity.
Moreover, the decline in secondary organic aerosol also influences regional climate patterns by modulating cloud properties and precipitation dynamics. The reduced CCN concentrations can lead to changes in cloud droplet number and size distributions, ultimately affecting cloud lifetime and geographic precipitation patterns. These microphysical alterations can feedback onto ecosystems and human activities, underscoring the interconnectedness of land-use, atmospheric chemistry, and climate.
The modeling approach used in this study elegantly combines satellite observations, land-use inventories, and advanced aerosol chemistry modules within a fully coupled Earth system framework. This allows for capturing the complex interactions between terrestrial biosphere alterations and atmospheric processes on a global scale, unlike previous models that simplified or ignored aerosol pathways related to land cover transformations. In doing so, it opens new avenues for understanding how anthropogenic landscape changes ripple through the Earth’s system in subtle but impactful ways.
From a policy perspective, these insights urge an integrated approach towards food security and climate change mitigation. As cropland expansion remains a key strategy for meeting global nutritional demands, the inadvertent side-effects on atmospheric composition and climate must be factored into land management and climate policy frameworks. Safeguarding or restoring forests could provide co-benefits not only for carbon sequestration but also for preserving natural aerosol production pathways that contribute to Earth’s cooling.
Furthermore, as global regulations succeed in lowering industrial aerosol emissions—a positive development for air quality and public health—the relative importance of biogenic aerosols in shaping the Earth’s radiation budget will grow. Understanding how human-driven changes to land surface characteristics influence these natural aerosols is essential for improving climate predictions and for designing robust climate interventions that do not overlook important feedback mechanisms.
These revelations also emphasize the need for better monitoring of biogenic VOC emissions under changing climatic conditions and land-use regimes. Improved empirical data will enhance the accuracy of models simulating secondary organic aerosol formation, their radiative properties, and their interactions with clouds. As the climate warms and vegetation shifts in distribution and physiology, real-time data from satellite and ground-based platforms will be indispensable to track evolving aerosol-cloud-climate feedbacks.
In summary, cropland expansion since industrialization has led to a significant reduction in biogenic secondary organic aerosols, weakening an important natural radiative cooling effect that partially offsets greenhouse gas warming. The magnitude of this effect rivals a substantial fraction of industrial CO₂-induced warming, highlighting how land-use changes reverberate through the Earth system in complex ways. Future projections indicate that as human emissions decline and the climate warms, these aerosol-mediated effects will become even more significant, demanding careful consideration in climate mitigation and land management strategies.
The study serves as a compelling reminder that the Earth’s climate system is intricately linked to the biosphere and that alterations to land cover ripple through the atmospheric chemistry and physics processes that regulate planetary energy balance. As humanity faces mounting pressures from climatic shifts and food demand, uncovering these nuanced interactions equips scientists, policymakers, and stakeholders with vital knowledge to navigate sustainable pathways for the planet’s future.
The researchers call for a reassessment of climate policies, emphasizing that preserving natural ecosystems offers benefits beyond carbon storage—specifically, the maintenance of crucial aerosol-related cooling effects. Integrating these considerations into the global discourse on climate change mitigation, sustainable agriculture, and land-use planning will be critical for aligning ecological stewardship with human development goals in the decades ahead.
Subject of Research: Radiative forcing effects of cropland expansion on biogenic secondary organic aerosol and associated climate impacts.
Article Title: Cropland expansion reduces biogenic secondary organic aerosol and associated radiative cooling.
Article References:
Zhu, J., Penner, J.E., Hong, C. et al. Cropland expansion reduces biogenic secondary organic aerosol and associated radiative cooling. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01718-z
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