During one of Earth’s most dramatic climatic upheavals, the Paleocene-Eocene Thermal Maximum (PETM), global temperatures surged dramatically, reshaping ecosystems and atmospheric dynamics on a planetary scale. A new study led by researchers from the State Key Laboratory of Lithospheric and Environmental Coevolution at the Chinese Academy of Sciences has provided unprecedented insights into the wildfire dynamics across northern China during this critical interval approximately 56 million years ago. By examining black carbon concentrations and stable carbon isotope ratios in sedimentary records from two key basins, the Beigou section of the Nanyang Basin and the Xilutian section of the Fushun Basin, the research team has elucidated the spatiotemporal evolution of fire activity and its intricate relationship with climate and vegetation shifts throughout the PETM.
The PETM is renowned as a striking example of rapid global warming, with surface temperatures increasing by approximately 5-8 °C within a few thousand years. This extreme warming was accompanied by a significant carbon isotope excursion (CIE), reflecting a massive release of ^13C-depleted carbon into the atmosphere-ocean system. The environmental consequences of such a perturbation include altered hydrological cycles, vegetation turnovers, and presumably wildfire regimes. However, the link between wildfire activity and paleoclimate conditions during the PETM has remained ambiguous, particularly in the Northern Hemisphere’s mid-latitude regions. This study fills a critical gap by employing black carbon (BC)—a robust marker of fire activity—in conjunction with total organic carbon (TOC) and isotopic signatures to reconstruct wildfire frequency, intensity, and ecological drivers over the PETM timeline.
The sediment core analysis revealed a marked and abrupt decline in wildfire proxies at the onset of the PETM, coinciding with the early phase of the carbon isotope excursion. The BC/TOC ratio, a proxy reflecting the relative abundance of fire-generated carbon relative to total organic matter, showed a sharp reduction in both the arid to semi-arid environment of the Nanyang Basin and the more humid conditions prevailing in the Fushun Basin. This decline persisted through the height of the PETM interval before a gradual resurgence during the recovery phase post-CIE. Interestingly, a transient spike in fire activity emerged mid-PETM in the Nanyang Basin but was otherwise absent in the Fushun region, highlighting differential regional responses to the overarching climate regime.
These findings contradict the intuitive expectation that elevated temperatures during the PETM would have fueled more frequent and intense wildfires. Instead, the data points toward a suppressive effect of the contemporaneous warm, humid climate on fire regimes. Palynological evidence from the Northern Hemisphere supports this interpretation, revealing vegetation shifts characterized by increased angiosperm and wetland plant dominance coupled with declines in gymnosperms and fern populations. The resultant landscape was less conducive to fire propagation due to higher moisture content in plant biomass and reduced continuity of flammable fuel beds, a phenomenon likely exacerbated by diminished seasonality and shorter or absent dry periods.
This climate-vegetation-fire feedback is further reinforced by geochemical evidence indicating substantial changes in carbon cycling during the PETM. A notable reduction in black carbon burial at the CIE onset signals diminished deposition of pyrogenic inert carbon, concomitant with increased sequestration of carbon in biologically active reservoirs such as soils, vegetation, and the atmosphere. Following the main phase of the PETM, during the CIE recovery interval, black carbon concentrations rose again, suggesting enhanced burial of inert carbon as the system gradually transitioned back toward pre-PETM conditions. This carbon sink shift from rapid, biologically mediated carbon pools toward long-term geological reservoirs underscores a complex interplay between wildfire dynamics and global carbon cycling.
At a mechanistic level, the researchers emphasize the role of hydrometeorological factors in modulating wildfire activity during the PETM. Excessive precipitation and persistently high humidity likely elevated fuel moisture content, impeding ignition probability and flame spread. Additionally, the proliferation of angiosperms, many of which typically exhibit lower flammability than gymnosperms, would have contributed to reducing the spatial continuity of burn-prone vegetation. This bioclimate synergy generated a landscape less hospitable to fire ignition and spread, thereby explaining the observed low wildfire activity across most of the Northern Hemisphere during this warming event.
The transient mid-PETM enhancement of wildfire activity observed in the Nanyang Basin may reflect localized climatic fluctuations or vegetation changes that temporarily favored fire ignition and propagation. Such episodic fire pulses suggest that regional or seasonal variability in climate factors still played a role in shaping fire regimes, even within an overall suppressive framework. However, the persistence of low fire activity over most of the PETM interval challenges previous assumptions that warming inherently increases wildfire prevalence, highlighting the importance of integrating multiple paleoproxies to disentangle climate-vegetation-fire interactions.
The implications of these findings extend beyond paleoecology, providing valuable analogs for contemporary climate change scenarios. As modern Earth experiences rising temperatures and shifting precipitation patterns, understanding the response of fire regimes to complex climatic variables becomes crucial for predicting ecosystem resilience and carbon feedbacks. The PETM’s muted wildfire activity despite intense warming serves as a cautionary example that temperature alone is insufficient to predict fire behavior, and hydrological context and vegetation composition must be considered to anticipate future fire dynamics accurately.
Furthermore, the documented shift in carbon cycling pathways during the PETM, highlighted by variable black carbon burial rates, indicates that wildfire activity can influence global carbon budgets over geological timescales. The interplay between fire suppressing factors and the sequestration of inert carbon pools may have moderated atmospheric carbon dioxide concentrations, acting as a negative feedback mechanism facilitating climate stabilization during the recovery phase. This insight illuminates the intricate role of fires not only as agents of ecosystem disturbance but also as components of Earth’s long-term carbon regulation processes.
The meticulous integration of geochemical analyses with sedimentological and palynological data in this study exemplifies the power of multidisciplinary approaches to reconstruct past environmental changes. By focusing on black carbon and stable carbon isotope records, the researchers illuminated nuanced patterns of wildfire activity tied to key climatic transitions during the PETM. The spatial comparison between the arid Nanyang Basin and humid Fushun Basin further strengthens the interpretive framework, demonstrating how varying regional climates mediated fire responses to global warming.
Ultimately, this investigation challenges preconceived notions of fire prevalence under warming conditions and underscores the importance of moisture availability, vegetation characteristics, and seasonality in determining wildfire patterns. The evidence from the PETM reveals that during intervals of extreme warmth but enhanced moisture, wildfire activity may be substantially curtailed, with significant implications for carbon cycling and ecosystem evolution. As the planet confronts rapid anthropogenic warming today, lessons drawn from deep time like these are invaluable for refining predictions of fire-related carbon feedbacks and guiding climate resilience strategies.
This pioneering research was published in Science China Earth Sciences and offers a critical new perspective on the complexities of wildfire-climate interactions during historic greenhouse episodes. Through advanced geochemical proxy analysis, Wang Xueting, Dr. Wang Xu, and Dr. Chen Zuoling have articulated a compelling narrative that integrates paleoclimate, vegetation dynamics, and fire regimes into a cohesive model of the PETM environment. Their work invites further exploration into how natural fire regimes have shaped Earth’s carbon and ecological trajectories over the eons.
Subject of Research: Spatiotemporal evolution of wildfire activity during the Paleocene-Eocene Thermal Maximum in China.
Article Title: Spatiotemporal evolution of wildfire activity during the Paleocene-Eocene Thermal Maximum in China.
News Publication Date: Not specified.
Web References: http://dx.doi.org/10.1007/s11430-024-1472-5
References: Wang X T, Chen Z, Cui L, Wang X. 2025. Spatiotemporal evolution of wildfire activity during the Paleocene-Eocene Thermal Maximum in China. Science China Earth Sciences, 68(2): 509–522.
Image Credits: ©Science China Press
Keywords: Paleocene-Eocene Thermal Maximum, wildfire activity, black carbon, carbon isotope excursion, PETM, paleoclimate, carbon cycling, paleofire, Northern Hemisphere, vegetation succession, climate feedback, sedimentary proxies
