Aerosols interact with radiation and clouds. Substantial progress made over the past 40 years in observing, understanding, and modeling these processes helped quantify the imbalance in the Earth’s radiation budget caused by anthropogenic aerosols, called aerosol radiative forcing, but uncertainties remain large. This review provides a new range of aerosol radiative forcing over the industrial era based on multiple, traceable and arguable lines of evidence, including modelling approaches, theoretical considerations, and observations. Improved understanding of aerosol absorption and the causes of trends in surface radiative fluxes constrain the forcing from aerosol-radiation interactions. A robust theoretical foundation and convincing evidence constrain the forcing caused by aerosol-driven increases in liquid cloud droplet number concentration. However, the influence of anthropogenic aerosols on cloud liquid water content and cloud fraction is less clear, and the influence on mixed-phase and ice clouds remains poorly constrained. Observed changes in surface temperature and radiative fluxes provide additional constraints. These multiple lines of evidence lead to a 68% confidence interval for the total aerosol effective radiative forcing of −1.60 to −0.65 W m−2, or −2.0 to −0.4 W m−2 with a 90% likelihood. Those intervals are of similar width to the last Intergovernmental Panel on Climate Change assessment but shifted towards more negative values. The uncertainty will narrow in the future by continuing to critically combine multiple lines of evidence, especially those addressing industrial-era changes in aerosol sources and aerosol effects on liquid cloud amount and on ice clouds.

https://hal.archives-ouvertes.fr/hal-02322106/document

Bounding global aerosol radiative forcing of climate change

Fires have influenced atmospheric composition and climate since the rise of vascular plants, and satellite data have shown the overall global extent of fires. Our knowledge of historic fire emissions has progressively improved over the past decades due mostly to the development of new proxies and the improvement of fire models. Currently, there is a suite of proxies including sedimentary charcoal records, measurements of fire-emitted trace gases and black carbon stored in ice and firn, and visibility observations. These proxies provide opportunities to extrapolate emission estimates back in time based on satellite data starting in 1997, but each proxy has strengths and weaknesses regarding, for example, the spatial and temporal extents over which they are representative. We developed a new historic biomass burning emissions dataset starting in 1750 that merges the satellite record with several existing proxies and uses the average of six models from the Fire Model Intercomparison Project (FireMIP) protocol to estimate emissions when the available proxies had limited coverage. According to our approach, global biomass burning emissions were relatively constant, with 10-year averages varying between 1.8 and 2.3 PgC yr-1. Carbon emissions increased only slightly over the full time period and peaked during the 1990s after which they decreased gradually. There is substantial uncertainty in these estimates, and patterns varied depending on choices regarding data representation, especially on regional scales. The observed pattern in fire carbon emissions is for a large part driven by African fires, which accounted for 58% of global fire carbon emissions. African fire emissions declined since about 1950 due to conversion of savanna to cropland, and this decrease is partially compensated for by increasing emissions in deforestation zones of South America and Asia. These global fire emission estimates are mostly suited for global analyses and will be used in the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations.

/pdf/historic-global-biomass-burning-emissions-for-cmip6-bb4cmip-1iufbhohwj.pdf

Historic global biomass burning emissions for CMIP6 (BB4CMIP) based on merging satellite observations with proxies and fire models (1750-2015)

1. Fire is a powerful ecological and evolutionary force that regulates organismal traits, population sizes, species interactions, community composition, carbon and nutrient cycling and ecosystem function. It also presents a rapidly growing societal challenge, due to both increasingly destructive wildfires and fire exclusion in fire-dependent ecosystems. As an ecological process, fire integrates complex feedbacks among biological, social and geophysical processes, requiring coordination across several fields and scales of study. 2. Here, we describe the diversity of ways in which fire operates as a fundamental ecological and evolutionary process on Earth. We explore research priorities in six categories of fire ecology: (a) characteristics of fire regimes, (b) changing fire regimes, (c) fire effects on above-ground ecology, (d) fire effects on below-ground ecology, (e) fire behaviour and (f) fire ecology modelling. 3. We identify three emergent themes: the need to study fire across temporal scales, to assess the mechanisms underlying a variety of ecological feedbacks involving fire and to improve representation of fire in a range of modelling contexts. 4. Synthesis: As fire regimes and our relationships with fire continue to change, prioritizing these research areas will facilitate understanding of the ecological causes and consequences of future fires and rethinking fire management alternatives.

/pdf/fire-as-a-fundamental-ecological-process-research-advances-1d1icv36g1.pdf

Fire as a fundamental ecological process: research advances and frontiers

Over the past 3.5 million years, there have been several intervals when climate conditions were warmer than during the pre-industrial Holocene. Although past intervals of warming were forced differently than future anthropogenic change, such periods can provide insights into potential future climate impacts and ecosystem feedbacks, especially over centennial-to-millennial timescales that are often not covered by climate model simulations. Our observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C. However, substantial regional environmental impacts can occur. A global average warming of 1–2 °C with strong polar amplification has, in the past, been accompanied by significant shifts in climate zones and the spatial distribution of land and ocean ecosystems. Sustained warming at this level has also led to substantial reductions of the Greenland and Antarctic ice sheets, with sea-level increases of at least several metres on millennial timescales. Comparison of palaeo observations with climate model results suggests that, due to the lack of certain feedback processes, model-based climate projections may underestimate long-term warming in response to future radiative forcing by as much as a factor of two, and thus may also underestimate centennial-to-millennial-scale sea-level rise.

/pdf/palaeoclimate-constraints-on-the-impact-of-2-c-anthropogenic-200f76gy5m.pdf

Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond

The important role of fire in regulating vegetation community composition and contributions to emissions of greenhouse gases and aerosols make it a critical component of dynamic global vegetation models and Earth system models. Over 2 decades of development, a wide variety of model structures and mechanisms have been designed and incorporated into global fire models, which have been linked to different vegetation models. However, there has not yet been a systematic examination of how these different strategies contribute to model performance. Here we describe the structure of the first phase of the Fire Model Intercomparison Project (FireMIP), which for the first time seeks to systematically compare a number of models. By combining a standardized set of input data and model experiments with a rigorous comparison of model outputs to each other and to observations, we will improve the understanding of what drives vegetation fire, how it can best be simulated, and what new or improved observational data could allow better constraints on model behavior. In this paper, we introduce the fire models used in the first phase of FireMIP, the simulation protocols applied, and the benchmarking system used to evaluate the models. We have also created supplementary tables that describe, in thorough mathematical detail, the structure of each model.

https://gmd.copernicus.org/articles/10/1175/2017/gmd-10-1175-2017.pdf

The Fire Modeling Intercomparison Project (FireMIP), phase 1: Experimental and analytical protocols with detailed model descriptions

. The location, timing, spatial extent, and frequency of wildfires are changing rapidly in many parts of the world, producing substantial impacts on ecosystems, people, and potentially climate. Paleofire records based on charcoal accumulation in sediments enable modern changes in biomass burning to be considered in their long-term context. Paleofire records also provide insights into the causes and impacts of past wildfires and emissions when analyzed in conjunction with other paleoenvironmental data and with fire models. Here we present new 1000-year and 22 000-year trends and gridded biomass burning reconstructions based on the Global Charcoal Database version 3 (GCDv3), which includes 736 charcoal records (57 more than in version 2). The new gridded reconstructions reveal the spatial patterns underlying the temporal trends in the data, allowing insights into likely controls on biomass burning at regional to global scales. In the most recent few decades, biomass burning has sharply increased in both hemispheres but especially in the north, where charcoal fluxes are now higher than at any other time during the past 22 000 years. We also discuss methodological issues relevant to data–model comparisons and identify areas for future research. Spatially gridded versions of the global data set from GCDv3 are provided to facilitate comparison with and validation of global fire simulations.

/pdf/reconstructions-of-biomass-burning-from-sediment-charcoal-2o49g53yug.pdf

Reconstructions of biomass burning from sediment-charcoal records to improve data–model comparisons

© 2018. Los Autores. Editado por la AEET. [Ecosistemas no se hace responsable del uso indebido de material sujeto a derecho de autor] Responder a las preguntas cada vez más complejas que abordamos, como profesionales de la ciencia o personas curiosas, implica la inclusión del mayor número de disciplinas, aproximaciones metodológicas y enfoques posibles. Esto es especialmente así cuando esas preguntas llevan implícitas la observación de dimensiones espaciales y temporales muy amplias; y en realidad una mirada atenta a la realidad casi siempre invita a pensar en el pasado para comprender lo que se ve. Con esta motivación y gracias a la oportunidad creada por el encuentro de MEDECOS y la AEET, celebrado en Sevilla en el mes de febrero de 2017, tres investigadoras muy interesadas en saltar la brecha intradisciplinar existente entre la paleoy la neoecología, decidimos proponer, por primera vez en este encuentro, una sesión enfocada a la paleoecología. Perseguíamos mostrar cómo estudiar los patrones y procesos en escalas temporales largas resulta esencial para entender mejor la ecología actual, pero no sólo eso. Ese viaje hacía el pasado con los ojos de quien vive el presente, es un viaje de ida y vuelta. Las proposiciones del uniformitarismo de Lyell implican que cualquier hipótesis que persiga explicar el pasado ha de encontrar análogos en el presente, tanto en forma de leyes, causas y efectos como en energía y grado (Lyell 1833; Gould 1987), y es en esto en lo que se anclan los principios interpretativos de la paleoecología y por lo que ambos enfoques deben desarrollarse paralelamente. Es por ello que bajo el título “Insights on the fourth dimension: the palaeoecological approach to modern ecological questions and viceversa”, se abrió este simposio inaugurado por la charla invitada de Lourdes López-Merino e incluyó seis contribuciones científicas (5 orales en distintos formatos (Fig. 1) y un póster). López-Merino hizo un recorrido sobre cómo su trabajo ha ayudado a la conservación de espacios naturales terrestres y marinos, siendo de especial relevancia su estudio sobre la dinámica holocena de las praderas de Posidonia oceanica (López-Merino et al. 2017). Las contribuciones fueron variadas en temáticas y escalas temporales: desde la paleobiología de mamíferos para comprender las redes tróficas actuales (Laura Domingo) o la respuesta de las metacomunidades de roedores a los cambios ambientales abruptos del Mioceno (Fernando Blanco Segovia), hasta estudios que proveían de nuevas aproximaciones metodológicas para integrar los indicadores ambientales del pasado (o proxies) en un marco metodológico que permita presentarlos con su incertidumbre asociada (Francisco Rodríguez-Sánchez) o incluso paquetes de R destinados a facilitar el acceso y el uso de bases de datos especializadas como la Europen Pollen Database (Diego Nieto-Lugilde). Además, hubo contribuciones desde la ecología moderna o en escalas temporales más cortas, centradas en el estudio de organismos actuales, como los foraminíferos, para entender su papel en el pasado (Anna Sabatinni) o la respuesta fisiológica de especies arbóreas ante cambios ambientales en escalas de siglos (Cristina Moreno-Guitiérrez). Nuestra experiencia organizando este simposio fue tremendamente positiva, observando que existe realmente un puente que salva la brecha, en parte creada sólo en nuestras mentes, entre el pasado y el presente para, en última instancia, ayudarnos a entender mejor el futuro. Nuestro deseo es que ese puente se mantenga, ya no sólo en sucesivas ediciones de los encuentros de la AEET, sino también en colaboraciones reales entre investigadores e investigadoras de diferentes áreas de la ecología.

https://revistaecosistemas.net/index.php/ecosistemas/article/download/1548/1105

Graciela Gil Romera

Papers

Reconstructions of biomass burning from sediment-charcoal records to improve data–model comparisons

Primer simposio sobre Paleoecología en el encuentro XIV de MEDECOS y XIII de la AEET