This study identified factors that affect climate change risk perception in a community college class. The purpose of this research was to determine if students were more influenced by cultural cognition (political affiliation) or science comprehension. Students in an undergraduate level environmental science and biology class were evaluated, using an online survey, for science comprehension level, political affiliation and risk perception at the beginning and end of each course. Data were analyzed to determine improved scientific literacy and any variation in risk perception. The research found that science comprehension did not contribute significantly to increased risk perception and that political affiliation or political views had a more significant effect on risk perception. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

Significant changes in climate and their impacts are now visible in various places around the globe and are expected to become more evident in the coming decades. For each increase in temperature, there are environmental and societal consequences. It has important implications for existing water resources systems as well as for future water resources planning and management. Water accounting (identifying, quantifying and reporting information of water flow in a system) is the first step towards formulating productive and sustainable water management strategies in a region. Thus, water balance models could be an empowering tool for water resource managers to prepare for and mitigate the effects of climate change on their local hydrologic resources. This thesis offers an insight into how such a tool can be used to assess and predict future stream flow trends in an effort to mitigate or manage any potential effects. / by Kevin Matthews. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Na década de 90 surge a primeira tentativa de gerar dados capazes de legitimar um modelo climático mundial detalhado: O Experimento de Circulação Oceânica Global (World Ocean Circulation Experiment - WOCE) Dentro dos diversos subprogramas inseridos no WOCE destaca-se o programa Hidrográfico (WHP). A JAMSTEC (Japan Marine Science and Tecnology Center), após cerca de uma década volta a reocupar algumas estações do WHP-WOCE, com o programa BEAGLE (Blue Earth Global Expedition), tendo como proposta detectar e quantificar alterações correspondentes ao aquecimento global. A I Comissão Oceanográfica Trans-Atlântica (TAI 2009) também constituiu um projeto de reocupação da seção A10, linha central do Oceano Atlântico Sul (~30?S), previamente amostrada pelo WHP-WOCE e BEAGLE, tendo como objetivo identificar alterações espaciais e temporais dos parâmetros oceanográficos nas últimas duas décadas. Considerando os valores de temperatura e salinidade foi evidenciada a presença de pelo menos, cinco massas d\'água: i) Água Tropical de Superfície (ATS) acima da isopícnal ?0= 26,70 ii) Água Central do Atlântico Sul (ACAS) abaixo da isopícnal ?1= 27,05 iii) Água Intermediária Antártica (AIA) abaixo da isopícnal ?2= 27,20 (iv) Água Profunda do Atlântico Norte (APAN) abaixo da isopícnal ?3= 27,70 v) Água Antártica de Fundo (AAF). Nas camadas superficiais dos três programas, notou-se uma proporcionalidade inversa entre as concentrações de nutrientes e oxigênio dissolvido. O Programa TAI ao longo de todo o transecto A10, apresentou as menores concentrações de nutrientes abaixo dos 1000 dbar. O WHP-WOCE foi mais aquecido que os outros programas nas camadas superficiais. Nas profundidades acima da termoclina (~1000 dbar), na bacia leste o Programa BEAGLE apresentou diferenciações que sugerem uma atividade mais intensa de ressurgência, para seu ano de amostragem do que nos anos dos Programas WHP-WOCE e TAI. Porém baseado nos resultados do Programa TAI, na extremidade leste da Bacia do Atlântico Sul, pode-se inferir que há afloramento da Água Central do Atlântico Sul (ACAS), provinda de aproximadamente 900 dbar de profundidade, sobre a Plataforma Continental Sul Africana. / In the 90s comes the first attempt of generate data able to legitimize a comprehensive global climate model: The Wolrd Ocean Circulation Experiment (WOCE). Within various subprograms inserted into the WOCE, highlight the WOCE Hydrographic Program (WHP). The JAMSTEC (Japan Marine Science and Technology Center), after about a decade back to reoccupy some stations of WOCE-WHP, with a program called BEAGLE (Blue Earth Global Expedition), proposing to detect and quantify changes related to global warming. The 1st Trans-Atlantic Oceanographic Commission (TAI 2009) was also created as a project of A10 section reoccupation, aiming to identify spatial and temporal changes in oceanographic parameters after two decades WOCE-WHP and BEAGLE sampling. The A10 section, represents the axis of South Atlantic Ocean (~ 30?S). Considering the values of temperature and salinity the presence of at least five water masses can be inferred: i) Surface Tropical Water (ATS) above isopícnal ?0 = 26.70, ii) South Atlantic Central Water (ACAS) below the isopícnal ?1 = 27.05 iii) Antarctic Intermediate Water (AIA) below the isopícnal ?2 = 27.20, (iv) North Atlantic Deep Water (APAN) below the isopícnal ?3 = 27.70, v) Antarctic Bottom Water (AAF). On the superficial layers of the three programs, it was noted an inverse proportionality between the concentrations of nutrients and dissolved oxygen. The TAI program, throughout the A10 transect, showed the lowest concentrations of nutrients below 1000 dbar. The warmer in the superficial layers was WOCE-WHP. On the layers above the thermocline (~ 1000 dbar), the BEAGLE Program around East Basin, showed some anomalies that suggest its sampling happened during some more intense upwelling activity, for its year than in years of WHP- WOCE and TAI programs. But based on the results of the TAI Program, at the east end of the South Atlantic Basin, it\'s possible to infer that there is upwelling of South Atlantic Central Water (ACAS), coming from about 900 dbar depth on the South African continental shelf.

Un futur climat planétaire plus chaud avec une sècheresse plus marquée durant toute l’année est aujourd’hui prévus, en particulier pour les hautes latitudes de l’hémisphère nord. Ces changements environnementaux seraient marqués par des fréquences et des intensités plus importantes des perturbations naturelles, qui pourraient menacer l’intégrité de certains écosystèmes forestiers boréaux. L’une des conséquences prévisibles serait une augmentation significative de l’occurrence des feux de forêt qui est déjà et deviendrait davantage encore l’élément perturbateur majeur de ces écosystèmes. Le devenir des écosystèmes boréaux suscite donc de nombreuses interrogations et des incertitudes, ce qui amène à souligner la nécessité d’une bonne caractérisation des changements climatiques spatio-temporels et de leurs conséquences sur ces écosystèmes.Afin de maintenir ces paysages forestiers dans les limites de leur variabilité naturelle, le Ministère des Forêts, de la Faune et des Parcs du Québec (MFFP) se propose, dans un contexte d’aménagement écosystémique durable, d’établir un Registre des états de référence. Dans cette perspective, l’objectif de recherche de cette thèse était de produire des reconstitutions des paléotempératures holocènes les plus robustes possibles au sein de la pessière à mousses de l’ouest du Québec. La recherche a porté sur une approche multi-indicateurs incluant les Chironomidae et le pollen contenus dans les sédiments des deux lacs retenus. Les résultats mettent en évidence la pertinence des capsules céphaliques de Chironomidae pour reconstituer à haute résolution temporelle, les paléotempératures holocènes du mois d’août provenant du Lac Aurélie à l’aide de deux Fonctions de Transfert (FT). La FT Est canadienne s’est avérée plus en accord avec le signal régional que la FT canadienne. De surcroit, les assemblages de Chironomidae du Lac Lili ont donné une reconstitution surestimée des paléotempératures en raison de la faible profondeur de ce lac. Enfin, la reconstitution quantitative combinée (Chironomidae et pollen) des paléotempératures du mois d’août a souligné trois périodes principales: (i) 8500-4500 ans AA, identifiée comme le Maximum Thermique de l’Holocène (HTM) durant laquelle les températures d’août sont plus chaudes que les températures actuelles; (ii) 4500-1000 ans AA, marquée par le début de la période Néoglaciaire froide, où les températures oscillent autour des valeurs actuelles et (iii) les derniers 1000 ans AA, caractérisés par une diminution générale des températures. Plusieurs événements climatiques courts ont également été identifiés pour chaque période : (i) l’évènement froid de 8200 ans AA; (ii) l’évènement chaud de 4200 ans AA; (iii) la période chaude dite Romaine (RWP, 1900-1700 ans AA) ; (iv) la période froide de l’Âge Sombre (DACP, 1700-1500 ans AA) ; (v) l’Anomalie Climatique Médiévale (MCA, 1100 ans AA) et (vi) le Petit Âge Glaciaire (LIA, 500-250 ans AA). Une série d’événements froids est également observée vers 5900, 4300, 2800 et 400 ans AA, se référant probablement aux évènements « Bond ». La durée et l’amplitude observées des événements climatiques rejoignent les enregistrements régionaux, nord-américains et plus largement ceux de l’Hémisphère Nord. Par ailleurs, la synthèse soulignant les relations entre climat-végétation-feu confirme l’influence d’une instabilité climatique sur les changements des régimes des feux, principalement causée par les variations saisonnières des précipitations et de l'irrégularité des épisodes de sécheresse. Toutefois, notre reconstitution combinée des paléotempératures indique que les grands feux coïncident avec l’évènement ponctuel de 4200 ans AA et ceux survenus à partir de 2000 ans (RWP, DACP, MCA et LIA). La température estivale conjuguée à d’autres variables climatiques (sécheresse estivale, ensoleillement estival, et précipitations annuelles) joue donc un rôle important dans la variation du régime des feux à l’ouest du Québec. / A future warmer global climate with more severe annual drought has been predicted, especially for the high latitudes of the Northern Hemisphere. Such an environmental change would be marked by higher frequencies and intensities of natural disturbances, which could threaten the integrity of some boreal forest ecosystems. One of the foreseeable consequences would be a significant increase in the occurrence of wildfires, which is already the major disruptive element of these ecosystems. The future of boreal ecosystems thus raises many questions and uncertainties, highlighting the need for a good characterization of spatio-temporal climate changes and its consequences on these ecosystems.In order to maintain these forest landscapes within the limits of their natural variability, the Ministère des Forêts, de la Faune et des Parcs du Québec (MFFP) proposes, in a context of sustainable ecosystem management, to establish a registry of reference states. In this perspective, the research objective of this thesis was to produce the most possible robust reconstructions of Holocene temperatures within the spruce-moss forest of western Québec. The research focused on a multi-indicator approach including Chironomidae and pollen deposited in the sediments of two selected lakes.The results highlight the relevance of Chironomidae head capsules to reconstruct at high temporal resolution the August Holocene temperatures from Lac Aurélie using two Transfer Functions (TF). The East Canadian TF was more in agreement with the regional signal than the Canadian TF. In addition, chironomid assemblages from Lac Lili gave an overestimated paleotemperature reconstruction due to the specific shallowness of this lake. Finally, the combined quantitative reconstruction (Chironomidae and pollen) of the August palaeotemperatures suggested three distinct periods: (i) 8500-4500 years BP, identified as the Holocene Thermal Maximum (HTM) during which the August temperatures are warmer than modern temperatures; (ii) 4500-1000 cal BP, marked by the beginning of the cold Neoglacial period, where the temperatures oscillate around the current values and (iii) the last 1000 cal BP, characterized by a general decrease of the temperatures. Several short climatic events were also identified for each period: (i) the 8200 cal BP cold event; (ii) the 4200 cal BP warm event; (iii) the Roman Warm Period (RWP, 1900-1700 cal BP); (iv) the Dark Age Cold Period (DACP, 1700-1500 cal BP); (v) Medieval Climate Anomaly (MCA, 1100 cal BP) and (vi) the Little Ice Age (LIA, 500-250 cal BP). A series of cold events is also observed around 5900, 4300, 2800 and 400 cal BP, probably corresponding to the "Bond" events. The observed duration and amplitude of climate events are consistent with regional, North American records, and more widely those of the Northern Hemisphere. In addition, the synthesis highlighting climate-vegetation-fire relationships confirms the influence of climatic instability on changes in fire regimes mainly driven by seasonal variations in rainfall and frequency of drought events. However, our paleotemperatures combined reconstitution indicated that large fires coincide with the occasional event of 4200 cal BP and those occurring from 2000 cal BP onwards (RWP, DACP, MCA and LIA). Summer temperatures combined with other climatic variables (summer drought, summer insolation, and annual precipitation) play an important role in the variation of the fire regime in western Québec.

O Atlântico Sudoeste comporta uma das regiões oceânicas mais energéticas do planeta: a Confluência Brasil-Malvinas (CBM). Essa região encerra o giro subtropical do Atlântico Sul e possui fundamental importância para a dinâmica desse oceano bem como para o clima regional. Através de saídas de modelos numéricos acoplados do 4°?elatório do IPCC, descreve-se o comportamento dessa região em dois cenários futuros de aquecimento global: um de elevada emissão de gases estufa (A1b) e o outro mais ameno em termos de impactos antrópicos (B2). Ambos os cenários apresentaram fortes tendências de aumento de temperatura sobretudo na superfície (chegando a 0,065°C/ano no cenário A1b e 0,055°C/ano no B2). A salinidade de superfície mostrou forte tendência positiva do Equador até a região da CBM, e negativa em maiores latitudes. A posição média da CBM desloca-se em aproximadamente 1,1° para sul no cenário A1b (entre 2066 e 2100) e 0,9° no cenário B2. O padrão espectral dessa posição (dominado pelo ciclo anual no século XX) é dominado pela variabilidade de baixa frequência no cenário A1b. Tais modificações na média e no espectro da posição da CBM estão associados à intensificação e mudança da Corrente do Brasil. / Southwestern Atlantic comprises one of the most energetic region of the world: Brazil-Malvinas Confluence (BMC). This region lies within the Southern Atlantic Subtropical Gyre and holds fundamental importance for this oceanic dynamics as well as for the regional climate. Through numerical modeling output coupled to IPCC\'s 4th Report, it is sunk to describe this region behavior for two distinct future scenarios: high greenhouse gases emission (A1b) and a milder one in terms of anthropic impacts (B2). Both scenarios have shown strong temperature increasing tendencies, especially on the surface (reaching up to 0.065°C/year in A1b and 0.055°C/year in B2). Surface salinity have also shown strong positive tendency from the Equator to the BMC region, and negative in higher latitudes. BMC medium position is shifted around 1.1°S in A1b scenario (between 2066 and 2010) and 0.9° in B2. Spectral pattern on this position (dominated for XX century annual cycle) is controlled by low-frequency variabilities in A1b scenario. These modifications in average and spectral patterns of BMC position are linked to the intensification and changing of Brazil current.

Between a Promise and a Trench examines how science is constituted as a strategic practice and site through which citizens make claims about racial democracy in Guyana. It shows how government policymaking around climate adaptation--which drew upon the recommendations of outside actors, including the Intergovernmental Panel on Climate Change (IPCC), the United Nations (UN), and various NGOs and international scientific networks-- profoundly disrupted the country's delicate racial-ethnic balance. A contribution to the burgeoning anthropology on the social and political impact of climate change, the dissertation also speaks to current debates over race and citizenship, the complex relationship between expertise and democracy, and the competing post-colonial claims of Indo-, Afro-, and Amerindian Guyanese to land and self-determination. The dissertation is based on seventeen months of fieldwork and archival research conducted between, 2009-11 in coastal Guyana. It brings together three conflicting perspectives: of engineers, who drew upon datasets and models about flooding and construction of canals around IPCC and UN climate data; the state officials, who sought to reduce vulnerability to flood hazards through land evictions; and of Indo-, Afro-, and Amerindian Guyanese farmers and squatters who were evicted as a result of post-2005 engineering projects. I use the concept "politics of vulnerability" to describe how states assume that citizens experience vulnerability to climate change based on their "ethnic-political status," thereby making the extension of democratic rights contingent on citizens providing cultural knowledge to the state to manage climate change. The dissertation attends to the consequences of the canals, including collapsed housing, failed civic science programs, and erratic water allocation. In response to these failures, citizens charge that state engineering repositions environmental hazards around existing social welfare inequities between racial-ethnic communities. During my time in Guyana, I tracked these responses at four distinct sites. 1) I observed engineers at work in the field produce and interpret "datasets" and "models" about flooding and construction of canals around IPCC and UN climate data. 2) I gathered residents' "unofficial" stories about vulnerability to floods through interviews and participant observations of everyday life in two coastal villages, Sophia (a racially mixed urban squatter community) and Mahaica (a predominately Indo-Guyanese cash crop community), where people were evicted due to the post-2005 engineering projects. 3) I analyzed "official" data generated through civic science projects and fieldwork in Mahaica and Sophia by engineers, state officials, and scientists that addressed vulnerability to flood hazards and its relationship to land evictions and property rights. 4) I conducted archival research in Guyana's National Archives on documents relating to colonial-era canals (1920s-60s) that inform the current projects. Although there is a growing ethnographic literature on climate change, a critical anthropology of vulnerability has yet to emerge. This dissertation offers two key interventions in this emerging field. First, I argue that in applied contexts, the validity of climate science is structured by the ways in which governments hinge climate adaptation projects to address varying national racial-ethnic populations. Second, I argue that governments cultivate institutions of social welfare that encourage "racial-ethnic" niche markets to manage vulnerability to climate change to soothe citizens' fears of state failure and environmental insecurity in the everyday. In such contexts, experiences of vulnerability become privatized, informing a consumer-oriented practice of racial democracy.

The role of the environment in the development process is frequently framed as a one-way interaction, with humans decoupling from natural systems, and often damaging them in the process. When the environment is granted an influential role, it is often in establishing the initial conditions under which development will take place, for example, through natural resource endowments or climate factors. However, in some extreme environments, it may be responsible for not only the initial opportunities available in a society, but also for continuously shaping those opportunities through time. The field of Sustainable Development is fundamentally concerned with this two-way interaction between the environment and society, recognizing both as part of a coupled system. The chapters in this volume demonstrate some of the costs associated with development in an extreme environment using methods from climate science, ecology, remote sensing, and economics. By looking at places exposed to tropical cyclones, to persistent pollution resulting from fires that burn readily in a drought-prone location, to annual floods that frequently and randomly strike households in a country, we see that the environment critically shapes aspects of societies and their economic opportunities. By no means are all opportunities dictated by the environment. However, these chapters robustly illustrate that the environment imposes some critical boundaries on development in extreme environments and policies aiming to increase welfare must take account of the coupling of social and natural systems.

The recent extreme hydrological extremes over the globe highlight the importance of understanding the role of atmospheric dynamics and climate variability on the occurrence of these extreme events and the associated temporal and spatial characteristics of sequences of the precipitation events. Most of the studies have been focusing on overall average impacts of long-term global climate change on extremes. Majority are driven largely by considering the changes of the moisture holding capacity as a function of temperature, as indicated by the Clausius-Clapeyron equation. Given the complex dynamical structure of the atmosphere, one needs to also consider the attendant atmospheric circulation and moisture transport mechanisms that lead to extreme precipitation and subsequent floods as evidenced in the recent major floods. This study first develops insights into the causative climatic factors associated with precipitation induced regional floods events and understand the roles of Atmospheric Rivers (AR) or Tropical Moisture Exports (TME) and atmospheric circulation patterns associated with the frequency and/or persistency of such events in the midlatitudes. The second part explores the spatiotemporal relationship between climate variability and global extreme precipitation occurrence using a graph based approach based upon the concept of reciprocity to investigated the linkages and influences of the slowly changing boundary conditions on the development or propagation of atmospheric circulations, to assess the predictability of global precipitation extremes given the leading modes of identified climate dipole networks. A multi-timescale statistical, climate informed, stochastic streamflow forecast model serves as the bridge linking the first two parts to the application in the third part: application on water resources management by developing a multi-timescale climate informed stochastic hybrid stimulation-optimization model for multi-purpose reservoir systems, which enables the utilization of the streamflow forecast. The novel reservoir operation model attempts to change the game of water resources management from its conservative, rigid rule-following scheme to a robust, market-based, reliable water allocation strategy. Part I. Tropical Moisture Exports, Extreme Precipitation and Major Flood Atmospheric Rivers are being increasingly identified as associated with some extreme floods. More generally, such floods may be associated with tropical moisture exports that exhibit relatively robust teleconnections between moisture source regions and flood regions. First, a large-scale flood event that persisted over Western Europe in January 1995 is studied. During the last ten days of the month, two rare flooding events, associated with heaviest rainfall in 150 years, occurred in two places, one over Brittany (West of France), and the second in the France-Germany border region and parts of neighboring countries. In this study, we explore the month-long evolution of tropical moisture exports (TME) and their connection to the precipitation events that led to the Brittany event. The persistent large-scale atmospheric circulation patterns that led to the birth, death and evolution of these TME as atmospheric rivers with landfalls in Western Europe are identified, and the relationship of daily extreme precipitation to these patterns is examined. Singular value decomposition (SVD) analysis and a generalized linear model (GLM) are used to assess whether knowledge of the atmospheric circulation patterns from the prior record is useful for explaining the occurrence of their rare events. The analysis establishes the importance of both global and regional atmospheric circulation modes for the occurrence of such persistent events and the hydrologic importance of diagnosing global atmospheric moisture pathways. Part II. Seasonal to Interannual Variability of Tropical Moisture Exports, Extremes and ENSO A statistically and physically based framework is put forward that investigates the relationship between Tropical Moisture Exports (TMEs), Extreme Precipitation and Floods. TMEs is the more general phenomena than Atmospheric Rivers (ARs) in terms of (1) facilitates the poleward transport of warm and moist air masses from low latitudes, primarily tropical oceanic areas, to higher latitudes; (2) contributes to the global climatology precipitation and its extremes; (3) closely relates to floods events, especially in the midlatitudes. The TMEs itself has seasonal and interannual variability that is regulated by slowly changing boundary conditions and climate variability, such El Niño Southern Oscillation (ENSO), while the trajectories and movements are presumably led by atmospheric circulations patterns driven by the balance of global energy and water budgets. In this study, we take Northwest US (NE US) to show how the TMEs is related to extreme precipitation and then floods, and the results of the variability of TMEs, coupled with atmospheric circulation patterns, on the extremes. Historical large floods events in NE US in different seasons are studied for their link to the TMEs. Major moisture sources of TMEs that contributes to precipitation, extremes and floods in NE US are identified, together with the sources' seasonally and interannually varying characterizes in terms of both birth and entrance to the NE US, with the consideration of large scale climate regulations and atmospheric circulation patterns. Part III. Correlation Networks for Identifying Predictors for Extended Range Forecasts for Extreme Precipitation Correlation networks identified from financial, genomic, ecological, epidemiological, social and climate data are being used to provide useful topological insights into the structure of high dimensional data. Strong convection over the oceans and the atmospheric moisture transport and flow convergence indicated by atmospheric pressure fields may determine where and when extreme precipitation occurs. Here, the spatiotemporal relationship between climate and extreme global precipitation is explored using a graph based approach that uses the concept of reciprocity to generate cluster pairs of locations with similar spatiotemporal patterns at any time lag. A global time-lagged relationship between pentad sea surface temperatures (SST) anomalies and pentad sea level pressure (SLP) anomalies is investigated to understand the linkages and influence of the slowly changing oceanic boundary conditions on the development of the global atmospheric circulation. We explore the use of this correlation network to predict extreme precipitation globally over the next 30 days, using a Principal Component logistic regression on the strong global dipoles found between SST and SLP. Unprecedented success of the predictive skill under cross validation for 30 days precipitation higher than the 90th percentile is indicated for selected global regions for each wet season considered. Part IV. Applications of Climate Informed Streamflow Forecasts for Water Management Streamflow forecasts at multiple time scales (e.g., season and year ahead) provide a new opportunity for reservoir management to address competing objectives. Market instruments such as forward contracts with specified reliability are considered as a tool that may help address the perceived risk associated with the use of such instruments in lieu of a traditional operation and allocation. A water allocation process that enables multiple contracts with different durations, to facilitate participatory management of the reservoir by users and system operators, is presented here. Since these contracts are based on a verifiable reliability they may in turn be insurable. A Multi-timescale climate informed Stochastic Hybrid Simulation - Optimization Model (McISH) is developed, featuring (1) dynamic flood control storage allocation at a specified risk level; (2) multiple duration energy/water contracts with user specified reliability and prices; and (3) contract sizing and updating to reflect changes in both demands and supplies. The model incorporates multi-timescale (annual and seasonal) streamflow forecasts, and addresses uncertainties across both timescales. The intended use is as part of an interaction between users and water operators to arrive at a set of short-term and long term contracts through disclosure of demand or needs and the value placed on reliability and contract duration. An application is considered using data for the Bhakra Dam, India. The issues of forecast skill and contract performance given a set of parameters are examined to illustrate the approach. Prospects for the application in a general setting are discussed.

Arctic air temperatures have increased at two to three times the global rate over the past century. As a result, abiotic and biotic responses to climate change are more rapid and pronounced in the Arctic compared to other biomes. One important change detected over the past several decades by satellite studies is a lengthening of the arctic growing season, which is due to earlier onsets and/or delayed ends to growing seasons. A handful of studies also suggest the peak green season (i.e. when the tundra is at maximum leaf-out and maximum carbon uptake potential) is starting earlier in the arctic tundra. The vast majority of studies detecting shifts in the growing season suggest this is due to increasing spring and fall air temperatures, which lead to earlier spring snowmelt and later fall snowfall. Less well understood is how indirect consequences of arctic warming, such as ongoing changes in plant community composition, may also be contributing to these satellite signals. For instance, there is mounting evidence that deciduous shrubs are expanding into previously non-shrub dominated tundra in several parts of the Arctic. Deciduous shrubs may alter tundra canopy phenology and contribute to the regional shifts in timing of phenological events being detected by satellites. Concurrently, in many areas where deciduous shrubs are expanding they are also becoming taller. As taller shrubs become increasingly dominant, arctic landscapes may retain more snow, which could lengthen spring snow cover duration, and offset advances in the start of the growing season that are expected as a result of earlier spring snowmelt. As a consequence, deeper snow and later snowmelt in taller shrub tundra could delay plant emergence, and shorten the period of annual carbon uptake. Thus greater dominance of taller stature deciduous shrubs in the Arctic may actually delay the onset of the growing season, which would suggest that increasing deciduous shrub dominance may not be contributing to satellite signals of an earlier start to the growing season. To contribute to satellite-detected shifts in the onset of the growing and peak seasons, tall deciduous shrubs would need to have accelerated leaf development to compensate for deeper snow packs and later spring snowmelt relative to surrounding tundra. Understanding the drivers of shifts in tundra phenology is important since longer (or shorter) growing and peak green seasons would increase (or decrease) productivity and the period of carbon uptake, which will have implications for landscape-level carbon exchange, and ultimately global carbon balances. Given the rate and magnitude of changes occurring in the face of acute arctic warming, there is a need to monitor, understand, and predict ecological responses over large spatial and temporal scales. However, compared to more southern environments, the arctic tundra is characterized by considerable heterogeneity in vegetation distribution, as well as a short and rapid growing season. In addition, the arctic tundra is relatively vast and inaccessible. These characteristics can make it difficult to monitor and study changes in the Arctic, and make it difficult to develop landscape-level models able to predict changes in ecosystem dynamics and tundra vegetation. The use of airborne and satellite sensors has at least partially fulfilled these needs to monitor, understand, and predict change in the Arctic. The normalized difference vegetation index (NDVI) acquired from these sensors, for instance, has become a widely adopted tool for detecting and quantifying spatial-temporal dynamics in tundra vegetation cover, productivity, and phenology. This suggests that remote sensing technology and vegetation indices may be similarly applied to characterizing patterns of primary and secondary consumers (e.g. arthropods), which would be enormously useful in a region as vast and remote as the Arctic. The research presented in this dissertation provides useful insight into the influence vegetation community composition, particularly increasing deciduous shrub dominance, has on phenology, carbon flux, and canopy arthropod biomass in the arctic foothills region of the Brooks Range, Alaska. Findings in Chapter one suggest that delayed snowmelt in areas dominated by taller shrubs may have a short-lived impact on the timing of leaf development, likely resulting in no difference in duration of peak photosynthetic period between tall and short- stature shrubs. Findings in Chapter two suggest that greater deciduous shrub dominance not only increases carbon uptake due to higher leaf area relative to surrounding tundra, but may also be causing an earlier onset of, and ultimately a net extension of, the period of maximum tundra greenness and further increasing peak season carbon sequestration. Findings in Chapter three suggest that measurements of the NDVI made from air and spaceborne sensors may be able to quantify spatial and temporal variation in canopy arthropod biomass at landscape to regional scales in the arctic tundra.

Northern Africa has experienced major shifts towards aridity and extensive C4 vegetation over the late Cenozoic, but due to a scarcity of spatially and temporally extensive paleoenvironmental records, the timing, patterns, and causes of these shifts are still under debate. Both long-term aridification and large amplitude orbital-scale climate variability have been recognized, with little understanding of how these two patterns relate to each other over time. African’s climate and environmental history of the last 7 Myr is of particular interest because hydrological and vegetation variability is considered the driving selection mechanism for human evolution. In addition, the age of the initiation of desert conditions in the modern Sahara desert, Earth’s largest warm desert and the largest source of dust to the modern atmosphere, is unknown. The stable isotope ratios of carbon and hydrogen in sedimentary plant leaf wax biomarker compounds have recently been shown to quantitatively track source vegetation photosynthetic pathways and the hydrogen isotope composition of plant source water, which is dominantly controlled by the amount of precipitation in Africa. These proxies have been applied to reconstruct long-term vegetation changes in East Africa and SW Africa over the last 14 Ma, as well as orbital-scale variability from various locations around the African continent, but they have not been extended further back in time or combined in tandem to robustly assess both long-term and orbital-scale climate and vegetation variability and how they relate to each other. In this thesis, I have utilized quantitative plant leaf wax stable isotope proxies to examine both orbital-scale and long-term changes in North African aridity and vegetation from a variety of regions over the last 25 Ma, with particular emphasis on the last 4.5 Ma. In Chapter 2, I investigated the evolution of hydrological and vegetation gradients from the equator to the sub-Sahara in NW Africa over the last 25 Myr using leaf wax stable isotopes at two marine sediment core locations, producing the longest existing leaf wax stable isotope record in Africa to my knowledge, and one of the longest such records globally. In this study I found that NW African environments were remarkably similar at both latitudes from 25 – 10 Ma, but at 10 Ma C4 vegetation abruptly expanded in the north, indicating sudden aridification in the Sahara region at that time. The hydrogen isotope record was stable long-term, with variability similar to that of known orbital-scale cyclicity in the Pliocene and Pleistocene, possibly suggesting that orbital-scale cyclicity or other factors obscured or were larger than any long-term changes in the hydrogen isotope ratio of precipitation. Saharan aridification at 10 Ma is consistent with climate model predictions of aridity due to the closure of the Tethys Seaway connection between the Indian Ocean and Mediterranean Sea near that time. The 10 Ma expansion in C4 vegetation is earlier than most other regions globally. To examine long-term changes in orbital-scale variability in the Eastern Sahara and Mediterranean Sea, I constructed a record of eastern Mediterranean sedimentary leaf wax carbon and hydrogen isotopes, leaf wax abundance, lignin biomarkers, and oxygen isotope ratios of planktonic foraminifera G. ruber during two 100-kyr periods of equal eccentricity near 3.0 and 1.7 Ma (Chapter 3). I found that precession-scale variability dominates the record during both periods, and Eastern Saharan precipitation and the vegetation assemblage, which was C4-dominated, do not change on average between the two periods. Chapter 4 extended the eastern Mediterranean record of Chapter 3 by sampling leaf wax stable isotopes in sapropel sediments (deposited during North African humid periods) at ~0.25 Myr resolution back to 4.5 Ma, placing the orbital-scale Chapter 3 results in long term context. I found that Eastern Saharan environments were persistently C4-dominated (>68%) throughout the entire interval, and that long-term hydrogen and carbon variability were similar in magnitude to orbital-scale cycles back to 4.5 Ma, strongly indicating that orbital-scale variability has been the dominant environmental control in NE Africa since the early Pliocene. This record contrasts sharply with observations of a transition from C3-C4 mixed vegetation to abundant C4 grasslands in East Africa over the same period of time. The results may suggest that long-term precipitation shifts did not occur in NE Africa since the Pliocene, or that the resolution of this approach is not sufficient to detect long-term shifts. It is likely that NW Africa also experienced similarly large hydrological variability over the same period of time, which may explain the unclear long-term hydrological signal in Chapter 2. The results emphasize that East Africa has not been representative of northern Africa as a whole since the Pliocene.