Daniel Brouse
March 6, 2026
Ozone may be a major contributor to climate change. It is also a significant threat to both plant and human health.
In the early 2000s, I became interested in ozone pollution and its relationship to climate change. Over the following decade, I began studying what I refer to as the ozone feedback loop, which has since become central to my research. Ozone may be one of the most significant non-CO₂ climate drivers contributing to the acceleration of climate change. Among other impacts, it appears to be playing a role in the weakening—and in some cases reversal—of major carbon sinks. In recent years, many of the world’s major forest systems have begun to show signs consistent with this troubling trend.
In this paper, I introduce the basic concepts behind the ozone feedback. Follow-up papers will examine how climate denial narratives frequently claim that the planet is “greening” due to excess CO₂, when in reality many ecosystems are showing increasing signs of browning, stress, and fire-driven degradation linked to the combined effects of CO₂, warming, and ozone exposure.
What drew me into this level of chemical detail was not abstract theory—it was something I observed directly over time.
From my third-floor office window, I could see the forest canopy. Over roughly ten years, I watched it slowly thin. At first the change was subtle, almost imperceptible. Then it became unmistakable. Trees that had stood for generations were losing density and height. The shift was disturbing, and the observation stayed with me for years.
It took several more years before I isolated what I now believe to be a major contributing factor: tropospheric ozone.
At ground level, ozone forms when pollutants from incomplete combustion—primarily nitrogen oxides (NOₓ) and volatile organic compounds (VOCs)—react in the presence of sunlight and heat. The resulting molecule is highly reactive. Some ozone molecules persist only briefly before reacting with other compounds, while others remain in the atmosphere for hours depending on local atmospheric chemistry. A small fraction may eventually migrate upward and contribute to stratospheric ozone, but most remains in the lower atmosphere where it forms and causes damage.
And it is a potent phytotoxin.
Ozone does not merely “stress” plants. It interferes with photosynthesis, weakens plant immune responses, and increases susceptibility to pests, drought, and heat. When warming temperatures, ozone exposure, and ecological stressors combine, the canopy decline I observed begins to make sense.
Volatile atmospheric compounds—especially short-lived reactive gases—can have disproportionate biological consequences.
In climate science, tropospheric ozone is classified as a short-lived climate forcer (SLCF). Unlike long-lived greenhouse gases such as carbon dioxide, which can remain in the atmosphere for centuries, ozone persists in the lower atmosphere for only hours to weeks depending on chemical and meteorological conditions. Despite its relatively short lifetime, it exerts a disproportionate influence on climate and ecosystems because it is continually regenerated through photochemical reactions.
Ozone functions as a greenhouse gas, absorbing infrared radiation and contributing directly to atmospheric warming. Although its radiative forcing is smaller than that of carbon dioxide or methane, its rapid formation and destruction make it an important component of the near-term climate system.
Tropospheric ozone is closely linked to methane chemistry. Methane oxidation in the atmosphere produces precursors that contribute to ozone formation. At the same time, the chemical processes that regulate ozone levels involve hydroxyl radicals (OH), which also control the atmospheric lifetime of methane. This creates a dynamic relationship in which methane emissions influence ozone production, while ozone-related chemistry affects how long methane persists in the atmosphere.
Aerosols add another layer of complexity. Certain aerosols scatter or absorb sunlight, altering the photochemical reactions that produce ozone. In some cases, particulate pollution reduces sunlight and suppresses ozone formation locally. In others, aerosol chemistry can promote reactions that enhance ozone production or modify atmospheric oxidant levels. These interactions mean that air pollution control strategies targeting particulates, methane, and nitrogen oxides can have cascading effects across atmospheric chemistry and climate dynamics.
From an energy perspective, tropospheric ozone contributes directly to the Earth’s energy imbalance. By absorbing infrared radiation, ozone traps additional joules of energy in the atmosphere, effectively accelerating warming. At the same time, its impact on vegetation reduces carbon uptake, which diminishes a natural sink for excess energy stored as carbon in biomass. In this way, ozone acts as both a direct amplifier of atmospheric energy and an indirect amplifier of the climate system, reinforcing feedback loops that multiply warming across coupled ecological and physical systems.
My current research focuses on climate feedback loops. Ozone appears to play a role in accelerating warming across multiple interacting systems, contributing to ecological stress and destabilization in areas such as:
Greenland and East Antarctic ice sheet tipping dynamics
Slowing of the Atlantic Meridional Overturning Circulation (AMOC)
Mountain glacier loss
Amazon rainforest dieback
Arctic sea-ice loss
Boreal forest degradation and wildfire
Permafrost thaw and combustion
Warm-water coral bleaching
West Antarctic Ice Sheet instability
What concerns me most is the interconnectedness—how atmospheric chemistry, biological stress, and physical climate systems can amplify one another through reinforcing feedbacks.
Ground-level (tropospheric) ozone is one of the leading environmental triggers of asthma in the United States and contributes to a wide range of respiratory and cardiovascular disorders. As a powerful oxidant, it damages lung tissue, increases inflammation, and raises the risk of hospitalization and premature death.
And the impacts extend far beyond human health.
Ozone is also a potent phytotoxin. It damages leaf tissue, reduces photosynthesis, stunts plant growth, and weakens vegetation against heat, drought, pests, and disease. Over time, this translates into reduced crop yields, declining forest health, and impaired carbon sequestration. As vegetation becomes stressed or dies back, the global carbon cycle is disrupted—carbon sinks weaken, emissions increase, and climate feedback loops intensify.
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