The far reach of fires

Wildfires are unplanned, uncontrolled events influenced by vegetation, weather, and landscape features. Although often associated with destruction, they play key ecological functions by clearing dead material, recycling nutrients, and promoting new growth. In fire-adapted ecosystems, fires can be beneficial when they occur in balance with their environment. However, anthropogenic climate and land use change have driven wildfires to become increasingly deadly and destructive. In this issue, we bring together papers focused on different aspects of fire impacts, which underscore how much they can vary. While broader environmental consequences of fires continue to unfold, the risks wildfires pose to human health are clear. A comprehensive understanding of the beneficial and harmful effects of wildfire is essential for the design of effective land-management strategies, restoration of ecosystem resilience, and preparation of vulnerable communities to live alongside wildfires.

Aerosols from wildfires contain nutrients that can boost ecosystem primary productivity far from the source. Fires in distant deforested and savanna regions can deliver phosphorus — a key nutrient for plant growth — to undisturbed areas of the Amazon, increasing forest productivity¹. Beyond terrestrial systems, wildfire emissions can also reach the ocean, where deposited aerosols can ease nutrient limitations and stimulate marine productivity, as shown by the widespread phytoplankton bloom driven by iron‑rich aerosols from the 2019–2020 Australian wildfires². These examples illustrate the far‑reaching ecological impacts of wildfire emissions, with fire activity in one region sustaining ecosystem functioning hundreds of kilometres away. However, these seemingly beneficial nutrient inputs are not necessarily a net ecological gain; they arise from fire regimes that are increasingly destructive and unpredictable, and that have been shown to exceed biological resilience thresholds, driving ecosystems towards a lower global carbon‑carrying capacity³.

Wildfires influence the climate, but the net effect depends heavily on local environmental conditions. In this issue, a Brief Communication by Wei Chen and colleagues uses integrated fire–atmospheric chemistry modelling to show that increased global fire emissions can reduce the atmosphere’s oxidation capacity, which allows methane to accumulate and thereby amplify warming. An Article in this issue by Max van Gerrevink and colleagues demonstrates that the climate impacts of fire are even more nuanced. The study found that boreal fires in Alaska generally cause net warming due to high fuel consumption and permafrost thaw, whereas in western Canada, post‑fire increases in surface albedo from longer spring snow exposure can produce net cooling. Together, the findings of these studies highlight the difficulty of extrapolating a universal future trajectory for the climate impacts of wildfires based on individual regions or events.

The consequences of wildfires extend beyond environmental systems and pose direct risks to human health. In the USA, wildfire emissions have increasingly shaped trends in annual concentration of fine particulate matter (PM_2.5), a pollutant regulated under the Clean Air Act, eroding decades of progress achieved through air pollution control efforts⁴. Wildfire-derived PM_2.5 levels in the USA are projected to cause more than 70,000 excess deaths per year by 2050 under a high warming scenario⁵. Financially, the health damages associated with climate-driven wildfire smoke could become the most expensive consequence of climate warming in the country⁵. Globally, these economic and health burdens are expected to be unevenly distributed, with Africa projected to experience the largest rise in fire-related premature deaths in the next century⁶. Reducing the inequitable mortality burden from wildfire smoke will require coordinated, proactive, and sustained intervention.

The repercussions of wildfire emissions ripple across domains. Wildfire emissions interact with atmospheric chemistry in ways that can amplify warming and diminish the planet’s capacity to buffer environmental changes. Increasing intensity and frequency of the most extreme wildfires⁷, together with the shifts in their spatial and temporal patterns, can result in measurable losses of lives, livelihoods, and economic stability. Because fire impacts unfold across spatial and temporal scales, future research and interventions must be similarly multidimensional. Only by assessing fire effects across their full spectrum, from transient, short‑lived pulses of nutrients and particulate matter to long‑term shifts in vegetation structure, biogeochemical cycles, and decadal climate feedbacks, can we design mitigation strategies that are both targeted and effective.