Testing the Tropical Trigger Hypothesis of Abrupt Climate Variability

This is the final version. Available on open access from Frontiers Media via the DOI in this recordDansgaard-Oeschger oscillations (DOs) are abrupt shifts in climate, which are dramatic temperature fluctuations observed in Greenland and recorded globally. These abrupt changes are associated with the slowing and shutting down of the Atlantic Meridional Overturning Circulation (AMOC), but despite their importance the driving forces of DOs are not fully understood. Here we assess the role of the AMOC during DOs, the Northern vs Southern Hemisphere control on AMOC, and the possibility of neotropical moisture as a driver for abrupt climate variability. During DOs, South America has recorded a disparity between the degree of warming, and the change in precipitation at different sites. Based on our current understanding, we propose likely oceanic and continental changes in tropical South America that can help disentangle the triggers of these events. With the margins of error associated with dating sources of palaeo-data, the need for an independent chronology with multiple proxies recorded in the same record, could offer the information needed to understand the driving forces of DOs.Natural Environment Research Council (NERC)PAGESINQU

Climate change communication in Colombia

This is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this record.Peru is one of the most biodiverse countries on the planet. More than 65% of the country is covered by the Amazon rainforest, and the Andes region is home to more than 70% of the world’s tropical glaciers. This abundance of natural resources also makes the country highly vulnerable to the effects of climate change. The Peruvian government therefore requires the development and implementation of action plans to adapt to the present and future impacts of climate change. At the same time, it requires the development of sound communication strategies that include collaboration with stakeholders such as the media and nongovernmental organizations. Media coverage of climate change can have important implications for policy decision making. This is especially salient in a context of low information availability where media reports play an important role in filling knowledge gaps that in turn can affect the way policies are developed. Climate change, as an environmental and social issue in Peru, is not highly politicized, as it is in countries such as the United States and Australia. There is no major debate about the reality of climate change, the scientific evidence, or the need for political action and technological and policy innovations. This approach is also reflected in the media’s coverage of the issue. Peru’s media tend to focus on climate change mostly during key policy events. Among these major events was the capital city of Lima’s hosting in 2010 of the V meeting of Latin American, Caribbean, and European Union countries, where the main topics of discussion were climate change and poverty. In addition, Lima hosted the COP20, which preceded the Paris meeting in 2015 that led to a major global agreement. The media’s coverage of these events was intense. These were the exceptions: A good proportion of Peru’s newspaper coverage comes from international news wire agencies. Coverage from those sources focuses mostly on mitigation actions, instead of adaptation, which is more relevant to vulnerable countries such as Peru. This coverage is in line with the government’s view of mitigation as a business opportunity. There is, however, a lack of studies that explore, first, the factors that affect this coverage, and, second, the way other mediums such as television or radio cover the issue. Strategic communication by governmental organizations, as well as accurate and fact-based media reporting about climate change, is necessary to better communicate the urgency and magnitude of the problem to the general public, grassroots organizations, industry, and international agencies, among others

New Insights From Pre-Columbian Land Use and Fire Management in Amazonian Dark Earth Forests

This is the final version of the article. Available from Frontiers Media via the DOI in this record.Anthropogenic climate change driven by increased carbon emissions is leading to more severe fire seasons and increasing the frequency of mega-fires in the Amazon. This has the potential to convert Amazon forests from net carbon sinks to net carbon sources. Although modern human influence over the Earth is substantial, debate remains over when humans began to dominate Earth's natural systems. To date, little is known about the history of human land use in key regions like the Amazon. Here, we examine the history of human occupation from a ~8,500 year-old sediment core record from Lake Caranã (LC) in the eastern Amazon. The onset of pre-Columbian activity at LC (~4,500 cal yr B.P.) is associated with the beginning of fire management and crop cultivation, later followed by the formation of Amazonian Dark Earth soils (ADEs) ~2,000 cal yr B.P. Selective forest enrichment of edible plants and low-severity fire activity altered the composition and structure of forests growing on ADEs (ADE forests) making them more drought susceptible and fire-prone. Following European colonization (1661 A.D.), the Amazon rubber boom (mid-1800s to 1920 A.D.) is associated with record-low fire activity despite drier regional climate, indicating fire exclusion. The formation of FLONA Reserve in 1974 A.D. is accompanied by the relocation of traditional populations and a fire suppression policy. Despite suppression efforts, biomass burning and fire severity in the past decade is higher than any other period in the record. This is attributed to combined climate and human factors which create optimal conditions for mega-fires in ADE forests and threatens to transform the Amazon from a net carbon sink to a net carbon source. To help mitigate the occurrence of mega-fires, a fire management policy reducing fire-use and careful fire management for farming may help to reduce fuel loads and the occurrence of mega-fires in fire-prone ADE forests. As both natural and anthropogenic pressures are projected to increase in the Amazon, this study provides valuable insights into the legacy of past human land use on modern ADE forest composition, structure, and flammability that can inform ecological benchmarks and future management efforts in the eastern Amazon.Funding for this research was supported by the PAST (Pre-Columbian Amazon-Scale Transformations) European Research Council Consolidator Grant to JI (ERC_Cog 616179). Research was conducted under permit 01506.004836/2014-69 from the Instituto do Patrimônio Histórico e Artístico Nacional (IPHAN) and ICMBio permit 106/14-FNT. We thank all residents of Maguarí and Jamaraquá community for their hospitality and help

Orbital-scale climate forcing of grassland burning in southern Africa.

This is the final version of the article. Available from the publisher via the DOI in this record.Although grassland and savanna occupy only a quarter of the world's vegetation, burning in these ecosystems accounts for roughly half the global carbon emissions from fire. However, the processes that govern changes in grassland burning are poorly understood, particularly on time scales beyond satellite records. We analyzed microcharcoal, sediments, and geochemistry in a high-resolution marine sediment core off Namibia to identify the processes that have controlled biomass burning in southern African grassland ecosystems under large, multimillennial-scale climate changes. Six fire cycles occurred during the past 170,000 y in southern Africa that correspond both in timing and magnitude to the precessional forcing of north-south shifts in the Intertropical Convergence Zone. Contrary to the conventional expectation that fire increases with higher temperatures and increased drought, we found that wetter and cooler climates cause increased burning in the study region, owing to a shift in rainfall amount and seasonality (and thus vegetation flammability). We also show that charcoal morphology (i.e., the particle's length-to-width ratio) can be used to reconstruct changes in fire activity as well as biome shifts over time. Our results provide essential context for understanding current and future grassland-fire dynamics and their associated carbon emissions.We thank Linda Rossignol for picking the foraminifera for carbon radiometric dating, Olivier Ther for XRF analysis, Marie-Hélène Castera and Muriel Georget for laboratory assistance, V. Hanquiez for extracting bathymetric data, Thibault Caley for providing the East African monsoon regression model data, Lydie Dupont for sharing the pollen data of cores GeoB1711 and MD96-2048, and Louis Scott for providing Wonderkrater’s charcoal data. This research was funded by European Research Council Advanced Grant TRACSYMBOLS 249587. The postdoctoral position of A.-L.D was funded by this project

Modern pollen-vegetation relationships along a steep temperature gradient in the Tropical Andes of Ecuador

This is the author accepted manuscript. The final version is available from Cambridge University Press via the DOI in this record.The characterization of modern pollen rain assemblages along environmental gradients is an essential prerequisite for reliable interpretations of fossil pollen records. In this study, we identify pollen-vegetation relationships using modern pollen rain assemblages in moss polsters (n = 13) and lake sediment surface samples (n = 11) along a steep temperature gradient of 7°C (3100–4200 m above sea level) on the western Andean Cordillera, Ecuador. The pollen rain is correlated to vascular plant abundance data recorded in vegetation relevées (n = 13). Results show that pollen spectra from both moss polsters and sediment surface samples reflect changes in species composition along the temperature gradient, despite overrepresentation of upper montane forest taxa in the latter. Estimated pollen transport distance for a lake (Laguna Llaviucu) situated in a steep upper montane forest valley is 1–2 km, while a lake (Laguna Pallcacocha) in the páramo captures pollen input from a distance of up to 10–40 km. Weinmannia spp., Podocarpus spp., and Hedyosmum sp. are indicators of local upper montane forest vegetation, while Phlegmariurus spp. and Plantago spp. are indicators for local páramo vegetation.Earth and Life Science council (ALW) of the Netherlands Organisation of Scientific Researc

Quantifying resilience of socio-ecological systems through dynamic Bayesian networks

This is the final version. Available on open access from Frontiers Media via the DOI in this recordQuantifying resilience of socio-ecological systems (SES) can be invaluable to delineate management strategies of natural resources and aid the resolution of socio-environmental conflicts. However, resilience is difficult to quantify and the factors contributing to it are often unknown. We provide a theoretical and conceptual framework to quantify resilience in a long-term context. Our approach uses elements from interdisciplinarity and network perspectives to establish links and causalities between social and ecological variables and resilience attributes. The evaluation and modeling of SES structure and function are established from the analysis of dynamic Bayesian networks (DBN). DBN models allow quantifying resilience through probabilities and offer a platform of interdisciplinary dialogue and an adaptive framework to address questions on ecosystem monitoring and management. The proposed DBN is tested in Monquentiva, a SES located in the high Andes of Colombia. We determined historical socio-ecological resilience from paleoecological evidence (palynological diversity, forest cover, fires, and precipitation) and social-economic factors (governance, social organization, and connectivity) between 1920 and 2019. We find that transformation processes in Monquentiva are mainly related to social change (e.g., social organization) and increased ecological diversity that in turn have fostered SES resilience between 1980 and 2019. The ability to predict the SES response over time and under cumulative, non-linear interactions across a complex ecosystem highlights the utility of DBNs for decision support and environmental management. We conclude with a series of management and policy-relevant applications of the DBN approach for SES resilience assessment.Natural Environment Research Council (NERC

Intensification of ENSO frequency drives forest disturbance in the Andes during the Holocene

This is the final version. Available on open access from Elsevier via the DOI in this recordThe biodiverse montane forests of the tropical Andes are today frequently disturbed by rainfall-driven mass movements which occur mostly during extreme El Niño events. Over the coming decades these events are projected to double under the 1.5 °C global warming scenario. The consequent increased rainfall and mass movement events likely present an elevated risk to millions of people living in the Andes. However, the impact of more frequent rainfall extremes remains unclear due to a lack of studies that directly link past changes in El Niño-Southern Oscillation (ENSO) frequency to forest and landscape disturbance patterns. Here, we present the first Holocene palaeoecological record from Laguna Pallcacocha, southern Ecuador, a key site for El Niño reconstructions. We demonstrate that for the past 10,000 years plant taxa indicative of recolonization – such as Alnus acuminata – covary with El Niño-induced flood layers in the lake. An amplified forest disturbance pattern is observed in the late Holocene, suggesting enhanced slope instability following deforestation. The temporal pattern is not explained by tree line fluctuations or human impact, while the latter does amplify the impact of ENSO on landscape disturbance. Spatial correlations between modern ENSO and precipitation are consistent with a regional comparison of Holocene records of landscape disturbance. Our results indicate that climate extremes, such as those associated with future intensification of El Niño, combined with ongoing land use change will increase the frequency of mass movements elevating risks for millions of people in the Andes.Earth and Life Science council (ALW), Netherlands Organisation of Scientific Research (NWO

The ACER pollen and charcoal database: A global resource to document vegetation and fire response to abrupt climate changes during the last glacial period

This is the final version of the article. Available from Copernicus Publications via the DOI in this record.Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard-Oeschger (D-O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D-O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73-15ka) with a temporal resolution better than 1000years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U/230Th, optically stimulated luminescence (OSL), 40Ar/39Ar-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft Access™ at https://doi.org/10.1594/PANGAEA.870867.The members of the ACER project wish to thank the QUEST-DESIRE (UK and France) bilateral project, the INQUA International Focus Group ACER and the INTIMATE-COST action for funding a suite of workshops to compile the ACER pollen and charcoal database and the workshop on ACER chronology that allow setting the basis for harmonizing the chronologies. Josué M. Polanco-Martinez was funded by a Basque Government postdoctoral fellowship (POS_2015_1_0006) and Sandy P. Harrison by the ERC Advanced Grant GC2.0: unlocking the past for a clearer future