Black carbon (BC) is produced by incomplete combustion of biomass by wildfires and burning of fossil fuels. BC is environmentally persistent over centuries to millennia, sequestering carbon in marine and terrestrial environments. However, its production, storage and dynamics, and therefore its role in the broader carbon cycling during global change, are poorly understood. In this Review, we discuss BC cycling across the land-to-ocean continuum. Wildfires are the main source of BC, producing 128 ± 84 teragrams per year. Negative climate–BC feedbacks could arise as wildfire increases with anthropogenic warming, producing more BC, which in turn will sequester carbon, but the magnitude of these effects are unknown. Most BC is stored in terrestrial systems with some transported to the ocean via rivers and the atmosphere. However, the oceanic BC budget is not balanced, with known BC removal fluxes exceeding BC inputs. We demonstrate these observed inconsistencies using a simple ocean box model, which highlights key areas of future research. Measurements of BC mineralization and export rates along the land-to-ocean continuum and quantification of previously unexplored sources of oceanic BC are needed to close the global BC budget. Black carbon is produced by wildfire and fossil fuel burning, and persists in the environment over centuries to millennia. This Review describes black carbon sources and budgets, discusses its transport along the land-to-ocean continuum and highlights its enigmatic cycling in the ocean. 

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The black carbon cycle and its role in the Earth system

Over the last decades, the natural disturbance is increasingly putting pressure on European forests. Shifts in disturbance regimes may compromise forest functioning and the continuous provisioning of ecosystem services to society, including their climate change mitigation potential. Although forests are central to many European policies, we lack the long‐term empirical data needed for thoroughly understanding disturbance dynamics, modeling them, and developing adaptive management strategies. Here, we present a unique database of >170,000 records of ground‐based natural disturbance observations in European forests from 1950 to 2019. Reported data confirm a significant increase in forest disturbance in 34 European countries, causing on an average of 43.8 million m3 of disturbed timber volume per year over the 70‐year study period. This value is likely a conservative estimate due to under‐reporting, especially of small‐scale disturbances. We used machine learning techniques for assessing the magnitude of unreported disturbances, which are estimated to be between 8.6 and 18.3 million m3/year. In the last 20 years, disturbances on average accounted for 16% of the mean annual harvest in Europe. Wind was the most important disturbance agent over the study period (46% of total damage), followed by fire (24%) and bark beetles (17%). Bark beetle disturbance doubled its share of the total damage in the last 20 years. Forest disturbances can profoundly impact ecosystem services (e.g., climate change mitigation), affect regional forest resource provisioning and consequently disrupt long‐term management planning objectives and timber markets. We conclude that adaptation to changing disturbance regimes must be placed at the core of the European forest management and policy debate. Furthermore, a coherent and homogeneous monitoring system of natural disturbances is urgently needed in Europe, to better observe and respond to the ongoing changes in forest disturbance regimes.

https://repozitorij.uni-lj.si/Dokument.php?dn=&id=164906

Significant increase in natural disturbance impacts on European forests since 1950

Fires can have an anthropogenic or natural origin. The most frequent natural fire cause is lightning. Since anthropogenic and lightning fires have different climatic and socio-economic drivers, it is important to distinguish between these different fire causes. We developed random forest models that predict the fraction of anthropogenic and lightning fire incidences, and their burned area, at the level of the Nomenclature des Unités Territoriales Statistiques level 3 (NUTS3) for Europe. The models were calibrated using the centered log-ratio of fire incidence and burned area reference data from the European Forest Fire Information System. After a correlation analysis, the population density, fractional human land impact, elevation and burned area coefficient of variation—a measure of interannual variability in burned area—were selected as predictor variables in the models. After parameter tuning and running the models with several train-validate compositions, we found that the vast majority of fires and burned area in Europe has an anthropogenic cause, while lightning plays a significant role in the remote northern regions of Scandinavia. Combining our results with burned area data from the Moderate Resolution Imaging Spectroradiometer, we estimated that 96.5 ± 0.9% of the burned area in Europe has an anthropogenic cause. Our spatially explicit fire cause attribution model demonstrates the spatial variability between anthropogenic and lightning fires and their burned area over Europe and could be used to improve predictive fire models by accounting for fire cause.

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Anthropogenic and Lightning Fire Incidence and Burned Area in Europe

Area burned has decreased across Europe in recent decades. This trend may, however, reverse under ongoing climate change, particularly in areas not limited by fuel availability (i.e. temperate and boreal forests). Investigating a novel remote sensing dataset of 64,448 fire events that occurred across Europe between 1986 and 2020, we find a power‐law relationship between maximum fire size and area burned, indicating that large fires contribute disproportionally to fire activity in Europe. We further show a robust positive correlation between summer vapor pressure deficit and both maximum fire size (R2 = .19) and maximum burn severity (R2 = .12). Europe's fire regimes are thus highly sensitive to changes in future climate, with the probability for extreme fires more than doubling by the end of the century. Our results suggest that climate change will challenge current fire management approaches and could undermine the ability of Europe's forests to provide ecosystem services to society.

Increasing aridity causes larger and more severe forest fires across Europe

Abstract Wildfire risk-management needs to consider interrelated factors that influence fire regimes, including changing climate and sometimes conflicting stakeholder priorities. With wildfires increasing in size and intensity over recent decades, wildfire risk management is becoming more important and more complex. For southwest Australia, wildfire risk-management is predicated on a longitudinal study of the relationship between prescribed burns and wildfires from 1953–2004 over a subset of this biodiverse region. Our study replicates the methodology of the longitudinal study, applying it to the wider region and extending the analysis to 2021. We found the extrapolation of the longitudinal study’s findings to the wider region invalid, as was extrapolation beyond 2004. In particular, the area of prescribed burns generally had negligible influence on wildfire area. However, more spatially complex fire history was strongly correlated with lower probability of large wildfires (independent of area burned). This highlights the limitation of extrapolating wildfire risk-management policies to areas of differing vegetation and/or climate, including changing climate over time. The potential of indigenous-led practices for wildfire risk and biodiversity conservation, particularly for areas with high spatial variability, is apparent as is the need for alternative strategies to prescribed burning as the primary tool in wildfire-risk mitigation.

https://www.tandfonline.com/doi/pdf/10.1080/19475705.2022.2119891?needAccess=true

Wildfire risk management across diverse bioregions in a changing climate

Recent wildfire outbreaks around the world have prompted concern that climate change is increasing fire incidence, threatening human livelihood and biodiversity, and perpetuating climate change. Here, we review current understanding of the impacts of climate change on fire weather (weather conditions conducive to the ignition and spread of wildfires) and the consequences for regional fire activity as mediated by a range of other bioclimatic factors (including vegetation biogeography, productivity and lightning) and human factors (including ignition, suppression, and land use). Through supplemental analyses, we present a stocktake of regional trends in fire weather and burned area (BA) during recent decades, and we examine how fire activity relates to its bioclimatic and human drivers. Fire weather controls the annual timing of fires in most world regions and also drives inter‐annual variability in BA in the Mediterranean, the Pacific US and high latitude forests. Increases in the frequency and extremity of fire weather have been globally pervasive due to climate change during 1979–2019, meaning that landscapes are primed to burn more frequently. Correspondingly, increases in BA of ∼50% or higher have been seen in some extratropical forest ecoregions including in the Pacific US and high‐latitude forests during 2001–2019, though interannual variability remains large in these regions. Nonetheless, other bioclimatic and human factors can override the relationship between BA and fire weather. For example, BA in savannahs relates more strongly to patterns of fuel production or to the fragmentation of naturally fire‐prone landscapes by agriculture. Similarly, BA trends in tropical forests relate more strongly to deforestation rates and forest degradation than to changing fire weather. Overall, BA has reduced by 27% globally in the past two decades, due in large part to a decline in BA in African savannahs. According to climate models, the prevalence and extremity of fire weather has already emerged beyond its pre‐industrial variability in the Mediterranean due to climate change, and emergence will become increasingly widespread at additional levels of warming. Moreover, several of the major wildfires experienced in recent years, including the Australian bushfires of 2019/2020, have occurred amidst fire weather conditions that were considerably more likely due to climate change. Current fire models incompletely reproduce the observed spatial patterns of BA based on their existing representations of the relationships between fire and its bioclimatic and human controls, and historical trends in BA also vary considerably across models. Advances in the observation of fire and understanding of its controlling factors are supporting the addition or optimization of a range of processes in models. Overall, climate change is exerting a pervasive upwards pressure on fire globally by increasing the frequency and intensity of fire weather, and this upwards pressure will escalate with each increment of global warming. Improvements to fire models and a better understanding of the interactions between climate, climate extremes, humans and fire are required to predict future fire activity and to mitigate against its consequences.

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Global and Regional Trends and Drivers of Fire Under Climate Change

Migratory stopover sites are of high conservation concern especially those sites where shorebirds concentrate in large numbers to acquire fat reserves to fuel continued flight to breeding grounds. Many shorebirds use only a few stopover sites during northward migration to Arctic breeding grounds, thus identifying important locations, migration chronology, and flight routes are priority research topics to inform effective management strategies. We examined Ruddy Turnstones (<em>Arenaria interpres</em>) route and timing to Arctic breeding grounds from an island in South Carolina in the heart of the South Atlantic Bight using the Motus Wildlife Tracking System. Ruddy Turnstones leaving South Carolina did not migrate northward up the Atlantic coast but migrated inland through the Great Lakes Basin. Most Ruddy Turnstones did not make a stop in the Great Lakes Basin, thus making South Carolina the last presumed stopover before reaching Arctic habitats. Like other shorebird migration studies, most of the Ruddy Turnstones made use of tailwinds at departure and ground speeds were positively correlated with tailwind support. Future conservation planning for Ruddy Turnstones must consider the varied migratory routes and strategies of this declining shorebird species. This research also demonstrates the usefulness of Motus for tracking the movement of smaller shorebirds and the potential for strategic expansion of the Motus network to understand their full life cycle. 

/pdf/south-atlantic-bight-a-final-stop-for-ruddy-turnstones-1na1k3nh.pdf

Adam J. P. Smith

Papers

Global and Regional Trends and Drivers of Fire Under Climate Change

South Atlantic Bight – a final stop for Ruddy Turnstones migrating to the Arctic

Past climate change responsible for rock uplift rate variation on the wasatch fault