Climate change has already increased the frequency, intensity, and duration of heat waves around the world. In the coming decades, this trend will continue and likely accelerate, exposing much of the world’s population to historically unprecedented conditions. In some regions, extreme temperatures (as indexed by the annual maximum temperature) are projected to increase at a faster rate than mean daily maximum temperatures. This dissertation shows that under a high emissions scenario, by 2060 – 2080 models project that the most extreme temperatures could warm by 1 – 2°C more than the warm season average in some regions. This amplified warming of the most extreme temperatures is most pronounced in the eastern U.S., Europe, eastern China, and parts of the Amazon rainforest, and may have substantial implications for heat risk in these regions. This dissertation explores the physical mechanisms driving the projected amplified warming of extremes in climate models and assesses the associated uncertainty. It shows that the amplification is linked to reductions in cloud cover, increased net surface shortwave radiation, and general surface drying as represented by declines in the evaporative fraction. In addition to rising temperatures, atmospheric humidity has been observed to increase in recent decades and models project this trend to continue. As a result, joint heat-humidity metrics indicating heat stress are likely to rapidly increase in the future. This dissertation explores how extreme wet bulb temperatures may change throughout the century and assesses the risk of exceeding a fundamental human heat tolerance limit that has been proposed in prior research. It then combines climate data with spatially explicit population projections to estimate the future population exposure to unprecedented wet bulb temperatures. Several regions stand out as being at particular risk: India, the coastal Middle East, and parts of West Africa are likely to experience extremely high wet bulb temperatures in the future, and rapidly growing populations in these regions will result in large increases in exposure to dangerous heat stress. In some areas, it is possible that wet bulb temperatures could occasionally exceed the proposed human tolerance limit by 2080 under a high emissions scenario, but limiting emissions to a moderate trajectory eliminates this risk. Nevertheless, even with emissions reductions, large portions of the world’s population are projected to experience unprecedented heat and humidity in the future. The projected changes in extreme temperatures will have a variety of impacts on infrastructure and other human systems. This dissertation explores how more frequent and severe hot conditions will impact aircraft takeoff performance by reducing air density and limiting the payload capacity of commercial aircraft. It uses performance models constructed for a variety of aircraft types and projected temperatures to assess the payload reductions that may be required in the future. These payload limits, along with sea level rise, changes in storm patterns, increased atmospheric turbulence, and other effects of climate change, stand to have significant economic and operational impacts on the aviation industry. Finally, this dissertation discusses evidence-based adaptation strategies to reduce the impacts of extreme heat in urban areas. It reviews a body of literature showing that effective strategies exist to both lower urban temperatures on a large scale and drastically reduce heat-related mortality during heat waves. Many adaptation techniques are not costly, but have yet to be widely implemented. Given the rapid increases in climate impacts that are projected in the coming decades, it will be essential to rigorously assess the cost-effectiveness of adaptation techniques and implement the most efficient strategies in both high- and low-income areas.

Unexpected melting of Northern Hemisphere ice sheets during periods of regional cooling characterizes the climate of the last glacial period. While the Heinrich Events are the most well-studied example of this phenomenon, Samuel Toucanne and colleagues recently documented evidence of Fennoscandian Ice Sheet melting during Heinrich Stadials, the cold periods during which Heinrich Events occur. In this dissertation, I use the geographic provenance of sediments in the Bay of Biscay, a proxy for Fennoscandian Ice Sheet melting, along with other paleoclimate records to: (1) demonstrate the persistence of abrupt Fennoscandian Ice Sheet melting as a feature of the Pleistocene climate system, (2) develop a self-consistent explanation for the synchronous melting of ice sheets in the North Atlantic region, and (3) elucidate the timing of abrupt climate change in the Northern Hemisphere. I begin by introducing a framework for inferring the subglacial transport distance of fine sediments from coupled provenance and grain size analyses. This chapter untangles the relationships between the source, size, transport history, and geochemical signature of glacigenic sediments in northern Europe, clarifying the geographical significance of sediment provenance in the Bay of Biscay. I then develop a new method for the spectral analysis of unevenly sampled time series. In the following chapter, I apply the new spectral method to time series of Fennoscandian Ice Sheet melting, Laurentide Ice Sheet melting, and solar activity changes during the last glacial period. Doing so reveals a coherence between ice sheet melting and solar activity and helps explain the quasi-periodic melting of ice sheets on millennial timescales. I then extend the neodymium isotope provenance record of Fennoscandian Ice Sheet melting through Marine Isotope Stage 6, demonstrating that enhanced summertime melting of the FIS during Heinrich Stadials is a recurring feature of glacial periods. In the final chapter, I document a relationship between the occurrence of abrupt ice sheet melting in the Northern Hemisphere and the precession of Earth’s spin axis to reveal an astronomical forcing of millennial-scale climate change.

The El Niño Southern Oscillation (ENSO), which refers to a coupling between equatorial Pacific Ocean and atmosphere anomalies, is a major source of interannual climate variability. Although it is fundamentally a tropical Pacific phenomena, both warm (El Niño) and cold (La Niña) events alter atmospheric circulations -- and subsequently temperature and precipitation patterns -- well into the mid- latitudes. Furthermore, both El Niño and La Niña have characteristic multi-year life cycles of sea surface temperature and zonal wind anomalies. The research in this thesis focuses on understanding whether the global teleconnections and multi-year evolution of El Niño and La Niña imposes a risk of synchronous or sequential crop failures relevant to global food production. In the first chapter, which focuses on maize, wheat and soy in the Americas, we analyze the dynamics underlying ENSO life cycles to illustrate which aspects of the system are most important for agriculture. In North America, the same-season teleconnections affecting soybean and maize have been well studied, but we demonstrate the importance of lagged soil moisture teleconnections for wheat in the southern Great Plains. In South America, peak ENSO sea surface temperature (SST) teleconnections are concurrent with, and therefore critical for, wheat and maize growing seasons while soil moisture memory in Argentina plays an important role during the soybean growing season In the second chapter we show how the teleconnections from chapter one lead to correlated crop production anomalies in North and South America. We estimate the magnitude of ENSO-induced Pan-American production anomalies and discuss how increasing crop harvesting frequency may affect Pan-American production variability. We find that ENSO-induced production anomalies are greatest for maize, with median anomalies of about 5% of Pan-American production. After broadly characterizing ENSO-induced production anomalies, we demonstrate that they are not static in time. Increasing crop harvesting frequency in Brazil has affected the correlated risks posed by ENSO to soybeans and maize. In the third chapter we expand our analysis of agriculturally relevant teleconnections to the greater Pacific Basin region, and move beyond observations into model simulations. In this chapter we propose a coherent framework for understanding how trans-Pacific ENSO teleconnections pose a correlated risk to crop yields in major agricultural belts of the Americas, Australia and China over the course of an ENSO life cycle. The potential for consecutive ENSO-induced yield anomalies is of particular interest in these major food producing areas, where modest changes in yield have significant effects on global markets. We demonstrate that ENSO teleconnections relevant for crop flowering seasons are the result of a single trans-Pacific circulation anomaly that develops in boreal summer and persists through the following spring. These trans-Pacific ENSO teleconnections are often (but not always) offsetting between major producing regions in the Americas and those in northern China or Australia. Multi-year La Niñas, however, only tend to force multi-year growing season anomalies in Argentina and Australia. In our final chapter we estimate of the relative contribution of major modes of climate variability to crop yield variability at the global scale. We consider the influence of not only ENSO, but also the Indian Ocean Dipole (IOD), tropical Atlantic variability (TAV) and the North Atlantic Oscillation (NAO). We find that modes of climate variability account for 18.4%, 7.4% and 5.4% of globally aggregated maize, soy and wheat production variability, respectively. All modes of variability are important in at least one region studied, but only ENSO has a significant influence on global production. The low fractions of global-scale soy and wheat production variability attributable to climate is a result of significant but offsetting ENSO-induced yield anomalies in major production regions. Our findings represent an observationally-derived limit on the importance of climate variability to crop production stability that is not dependent on the fidelity of present generation of climate or crop models. In terms of synchronous crop failures within a single harvest year, we find that ENSO poses a significant correlated risk to maize yields but that it has a much smaller effect on global wheat and soy production. ENSO-forced maize production anomalies offset less than wheat and soy at the global scale because production is concentrated in regions with same-sign yield anomalies, notably the United States and Southeast Africa. To illustrate this point, we show that ENSO is largely responsible for the largest synchronous maize failure in the post-1960 historical record. These results demonstrate how the distribution of global cropland in relation to ENSO teleconnections contributes significantly to the presence for maize or absence for wheat and soy of synchronous global crop failures

Due to the wide range of physical scales involved, clouds cannot be fully resolved in models of the global climate, and so are parameterized. The resultant model deficiencies in simulating important cloud processes within the current climate are strongly implicated in the large uncertainty in model predictions of future climate changes. Previous work has highlighted the uncertainties in predictions of future climate related to thermodynamic cloud changes, understanding of which requires detailed observations of small-scale cloud microphysics. In this thesis, we argue that understanding the linkages between mid-latitude clouds and the general circulation of the atmosphere can advance efforts to constrain their response to climate forcing. We make this argument with three main methods of analysis: 1) observations, 2) state-of-the-art general circulation models, and 3) experiments with an idealized model of the global climate. First, we perform a comprehensive investigation of the observed inter-annual relationships between clouds, their radiative effects, and key indices of the large-scale atmospheric circulation. Using reanalysis data and satellite retrievals, we find a relationship between the edge of the Hadley circulation (HC) and the high cloud field that is largely robust against season and ocean basin. In contrast, shifts of the mid-latitude eddy-driven jet latitude, which had been the focus of previous work on the coupling between mid-latitude clouds and circulation, only correlate with the high cloud field in the wintertime North Atlantic. In that season and basin, poleward shifts of the circulation are associated with anomalous shortwave cloud radiative warming. During all seasons in the Southern Hemisphere, however, poleward shifts of the circulation are associated with anomalous shortwave cloud radiative cooling. Second, we examine Coupled Model Intercomparison Project phase 5 (CMIP5) model output to evaluate the models' simulation of the inter-annual co-variability between the Southern Hemisphere HC extent and the shortwave cloud radiative effect. In the control climate runs, during years when the HC edge is anomalously poleward, most models reduce their cloud cover in the lower mid-latitudes (approximately 30$^\circ$S - 45$^\circ$S) and allow more sunlight to warm the region, although we find no such shortwave radiative warming in observations. We correlate these biases in the co-variability between the HC extent and shortwave cloud radiative anomalies with model biases in the climatological HC extent. Models whose climatological HCs are unrealistically equatorward compared to the observations exhibit weaker climatological subsidence in the lower mid-latitudes and exhibit larger increases in subsidence there with poleward HC extent shifts than models with more realistic climatological HCs. This behavior, based on control climate variability, has important implications for the model response to forcing. In 4$\times$CO$_2$-forced runs, models with unrealistically equatorward HCs in the control climatology exhibit a stronger shortwave cloud radiative warming response in the lower mid-latitudes and tend to have larger values of equilibrium climate sensitivity than models with more realistic HCs in the control climatology. The above correlative analyses suggest that uncertainty in the linkages between mid-latitude clouds and the general circulation of the atmosphere contributes to uncertainty in the model response to forcing. Finally, we use simulations of the global climate in an idealized aquaplanet model to show that the biases in the climatological Southern Hemisphere circulation do indeed contribute to much of the model spread in the cloud-circulation coupling. We find that for the same 1$^\circ$ latitude poleward shift, simulations with narrower climatological HCs exhibit stronger mid-latitude shortwave cloud radiative warming anomalies than simulations with wider climatological HCs. The shortwave cloud radiative warming anomalies result predominantly from a subsidence warming of the planetary boundary layer, which decreases low-level cloud fraction and is stronger for narrower HCs because of a tighter mean meridional circulation. A comparison of the spread across aquaplanet simulations with that across CMIP5 models suggests that about half of the model uncertainty in the mid-latitude cloud-circulation coupling stems from this impact of the circulation on the large-scale temperature structure of the boundary layer, and thus can be removed by improving the representation of the climatological circulation in models. Therefore, a more realistic representation of the Hadley circulation in models can improve their representation of the linkage between mid-latitude clouds and the atmospheric circulation in the current climate and increase overall confidence in predictions of future climate.

Recent increase in forest mortality events worldwide and their relationship with drought episodes highlight the importance of understanding tree resilience to a changing climate. Empirical models of forest mortality have been typically used and were focusing on carbon related variables such as growth to predict tree death. Recent efforts have shifted toward a more mechanistic modeling of mortality. Mechanistic approaches use tree traits and climate as inputs to model processes and represent carbon and water fluxes, all necessary to plant life. The advantage of mechanistic approaches is their ability to account for potential adaptation of trees to climate change, but also to physically explore the causes of vulnerability and resilience to droughts. Mechanistically, the atmospheric demand for moisture at the canopy level is communicated to the tree through stomata, creating a water gradient between the leaves and the roots, and resulting in the ascent of sap via the plant hydraulic structure. Depending on the climate (temperature, atmospheric dryness, light, precipitation), different architectures will perform differently at maintaining the gradient. For example, deep roots can access deep water in dry regions and shallow roots can access rare precipitation events whereas larger leaf area increases the atmospheric demand for moisture. In very harsh conditions such as extreme or lasting droughts, the hydraulic structure might suffer from a steep water gradient. Protection against excessive gradients can be achieved either through an investment in a stronger structure (denser wood) or through a regulation of the pulling force at the top of the canopy (closing leaf stomata). Evolution of structures and physiological strategies have resulted in fitness advantages and partially explain the diversity of species architectures across climates. More importantly, this diversity is at the core of the vulnerability and resilience of each species to increased aridity and frequency of extreme events, and therefore its mortality. This dissertation investigates the resilience to droughts of two co-occuring species in common woodlands of New Mexico, USA. This location is of specific interest because drought conditions (high temperature and/or low precipitation) have become more frequent as a result of global warming and because these ecosystems have suffered extensive mortality in the last decades. The two species, Pinus edulis and Juniper monosperma have very different physiological strategies, which allows for an extra level of vulnerability comprehension. To further test their resilience to extreme drought and possibly future climatic conditions, I studied trees that were subject to a six-year rain-reduction experiment. In the first part we develop a mechanistic model of the tree functioning that includes water and carbon fluxes and is based on their respective supply-demand balances. We use this simplified mechanistic model to study the sensitivity of mortality to hydraulic structure variations and to the physiological strategy of each species. We find that for both species death resulted from an irreversible damage of tissues transporting water. Despite P. edulis’s ability to close stomata to reduce the atmospheric demand, they died first because of their vulnerable tissues. In the second part, I specifically investigate P. edulis’s structural response to drought at the canopy level. By dissecting branch anatomy at an annual resolution, I find that during droughts this species increase relatively more leaf area (water demand) compared to transport area (water supply). I suggest that the structural adjustments that occur at the branch level do not contribute to the protection of the tissues transporting water. In the third part, I analyze the anatomy of these tissues in branches of P. edulis. I find that in response to long-lasting drought the trees built tissues more efficient at transporting water but also more vulnerable to future drought. By contrast, a short-intense drought decreases efficiency without changing vulnerability. I hence show that during lasting drought the anatomical adjustment of branch tissues increase the vulnerability of the piñons. This study shows the importance of considering climate responses of structure and physiology together to compare resilience across species. It also shows that adjustments of hydraulic elements in response to drought tend to decrease hydraulic resilience and could favor a run-away scenario. If the population of Pinus edulis - a dominant species of the Southwest US - were to decline, major shift should be expected in related ecosystems.

The Mackenzie River Delta is an ecologically rich freshwater environment in Canada’s Northwest Territories. It is vulnerable to multiple stressors such as climate change, resource development activities (oil and natural gas) and upstream-downstream linkages related to extraction activities in the southern part of the Mackenzie River watershed. Resultant socio-ecological impacts affect fishing livelihoods, which represent a significant component of the country food system and ways of life for Inuvialuit (Inuit of the Western Arctic), whose Settlement Area overlaps with the Delta. This thesis analyzes the implications of socio-ecological changes in the Mackenzie River Delta for Inuvialuit fishing livelihoods and the country food system, drawing from Local and Traditional Knowledge. In collaboration with the Fisheries Joint Management Committee in the Inuvialuit Settlement Region, the westernmost Inuit region in Canada, I undertook a participatory-qualitative research, while also drawing on relevant literature and complementary data. Using 28 semi-structured interviews about changes in the Mackenzie River Delta and the importance of fishing livelihoods, results indicated that fishing livelihoods are essential contributors to the Inuvialuit food system, as well as cultural practices surrounding fishing as an activity. Moreover, some results imply the importance of previously ignored species for food security, such as burbot and inconnu, which receive limited attention in other studies. Key findings also indicate that multiple environmental changes are occurring in the Delta, including lower water levels, increasing land erosion, decreasing fish populations, and changes in Delta-reliant wildlife populations (e.g. more beavers), warmer water temperatures, poorer fish quality (e.g. softer flesh, parasites), thinner ice, climate variability, and an escalating cost of living. These changes affect primarily fishing access and raise important concerns about the safety of fish consumption for human health. Ultimately, limited access and declining fish quality have a negative impact on food security, given the key role of fish in the country food system and the importance of socio-cultural dimensions such as fishing knowledge and skills, and sharing practices.

Na área de serviços, e mais especificamente no segmento hoteleiro - que tem enfrentado, como em outros segmentos de negócios, um grande aumento de concorrência, aliado ao aumento do nível de exigência dos consumidores - o diferencial representado pelas pessoas, que fazem parte da organização, é mais do que uma vantagem competitiva: é uma questão de essência. Afinal, o negócio hoteleiro está associado ao conceito de hospitalidade, e a hospitalidade, em sua essência, é um atributo de pessoas, e não de lugares ou de instalações. Considerando que a cultura organizacional (CO) de uma empresa pode ou não possibilitar a superação deste tipo de desafio de caráter humano, realizou-se um estudo de caso em um hotel que buscou um reposicionamento mercado lógico, com o objetivo de observar como esta mudança se refletiu na cultura da organização. Optou-se pela metodologia qualitativa, utilizando-se como instrumentos pesquisa documental, entrevistas e observação participante. Os resultados desejados pelos gestores, em termos de produtividade, foram alcançados. Observaram-se mudanças organizacionais importantes, impostas no estilo \'top-down\' e que ocorreram no nível mais superficial da cultura. Não houve alteração no sistema de valores ou nas políticas institucionais. Os resultados positivos em termos de produtividade fundamentaram-se nos valores das equipes orientadas para a satisfação do cliente e para a hospitalidade. Valores e normas, já estavam internalizados desde o processo de socialização no hotel, sendo que a mudança em procedimentos não chegou a afetar este aspecto. Conclui-se que o grande desafio desse empreendimento é o desenvolvimento de uma CO que conjugue profissionalismo e afetividade. / Considering the services area, specifically the lodging industry which has facing, just like others business segments, a huge concurrence and growing level of consumers\' exigency - the differential represented by human beings, which are part of the organization, is not just a competitive advantage: it is an essence issue. After all, the hotel business is related to the hospitality concept, and hospitality, in its essence, it is an attribute of people, and not an attribute of places or accommodations. Considering the importance of the people in a lodging organization, and that the behavior of these people influences and it\'s influenced by the organizational culture, justify a deeper look to the cultural elements which defines behavior patterns. In this way, it introduces a study case in a hotel that looked for a marketing repositioning, and it involved relevant organizational changes. The information collected on documental research, interviews with managers and employees, and participant observation tried to understand how the organization culture makes the hotel and the people be how they are. The data analyses suggest that changes were made on superficial levels of culture, and the managers\' desired results, in productivity terms, were reached.

This thesis seeks to examine the politics of building resilience to climate change by analysing the manner in which policy contexts and initiatives to build climate change resilience interact. For analysis, the ‘policy context' is broken into its three constituent parts- actors, policy spaces and discourses. This permits the addition of new knowledge on how discourses attached to resilience are dissonant with those prevailing in ossified policy environments in developing countries; the influence of actor networks, epistemic communities, knowledge intermediaries and policy entrepreneurs in helping climate change resilience gain traction in policy environments; and the dynamic interaction of interest, agendas and power within decision-making spaces attached to resilience-building processes. This analysis takes place by employing a case-study of a major, international climate change resilience initiative unfolding in two Indian cities. Using data gathered through a variety of rigorous qualitative research methods employed over 14 months of empirical inquiry the thesis highlights issues of politics and power to argue that they are significant determinants of processes to deal with climate impacts. More specifically, it expands current understandings of engaging with climate impacts by exposing gaps in resilience thinking and argues against a technocratic approach to designing and executing resilience policies. In doing so it also demonstrates that resilience, with its emphasis on systems thinking, dealing with uncertainty and community engagement brings new challenges for policy makers. As the study is located in the urban context, it highlights the manner in which fragmented urban policy environments, dense patterns of settlement in cities, urban livelihood patterns and prevailing epistemic cultures can pose obstacles for a policy initiative aimed at building resilience to climate change. Finally, the research underlines the importance of coupling resilience with local narratives of dealing with shocks and stresses, argues for genuine iteration and shared learning during decision-making and highlights the need to celebrate multiple visions of resilience. Findings from this research can help inform a growing number of policy initiatives aimed at deploying resilience to help those battling the exigencies of a changing climate in some of the world's most vulnerable areas.

This research addresses the following question: ‘In the context of climate change, how do different actors narrate the uncertain, ambiguous and risky future of maize agriculture, and what are the implications?' A multi-sited and institutional ethnography approach was adopted in order to look critically at how knowledge and narratives of future change in Kenyan maize agriculture are constructed by a variety of actors. The thesis describes: contested narratives of climate change and climate change impacts (through an analysis of the global climate impact modelling endeavour); contested narratives of change on smallholder farms (based on two case study sites in Kenya); contested narratives of pro-poor technological interventions (including the development of genetically modified drought tolerant maize); and contested narratives of technology regulation (with a focus on Kenyan biosafety policy). It is shown that narratives are contested in multiple sites and by a variety of actors and, although the resolution of these contestations often fall along familiar lines of power and elite capture, there are examples in which alternative perspectives find agency. This is the case not only in national policy-making arenas and the board-rooms of international development initiatives, but also in the fields and communities of smallholder farmers, the offices of national research centres, and the operations of civil society organisations. It is argued that, within these diverse settings, critical analysis of the constructed nature of knowledge is a necessary foundation on which to open up the negotiation of Kenya's agricultural future to multiple alternatives.

One central goal in ecology is to understand how biodiversity, and key organismal traits, interact with ecosystem properties and processes, and ultimately to understand and predict how these interactions will be affected by rapid environmental change. Thus, global change experiments and observational gradients in diversity provide the opportunity to examine and test hypotheses about how organismal traits, multiple dimensions of biodiversity, and ecosystem function will respond to environmental change. In Arctic tundra, increased nitrogen (N) and phosphorus (P) availability accompanying rapid warming is thought to significantly alter plant community composition and ecosystem function. The following four chapters examine hypotheses about the responses of species’ traits, multiple dimensions of biodiversity, and ecosystem function to the effects Arctic warming. Chapter 1 examines plant community composition and the capacity for ecosystem function (net ecosystem exchange, ecosystem respiration, and gross primary production) across a gradient of experimental N and P addition expected to more closely approximate warming-induced fertilization, demonstrating declines in plant diversity and an increase in the capacity for ecosystem carbon uptake at the highest level of fertilization. Chapter 2 examines a set of physiological and functional leaf traits across the same N and P gradient in order to evaluate the possible physiological mechanisms underlying community and ecosystem responses, highlighting the effects of increasing nutrient availability for deciduous shrub species. Chapter 3 found that single-dose, long-term nutrient addition (i.e., > 20 years) led to significant declines in multiple dimensions of diversity (taxonomic, functional and phylogenetic), and that these effects persist through time, increasing for dimensions that capture organismal traits (functional and phylogenetic). Finally, Chapter 4 examined the relationship between multidimensional diversity and ecosystem function across a natural gradient of diversity, and found that taxonomic diversity and functional diversity were significantly and positively related to whole ecosystem productivity, and, conversely, functional evenness and dispersion were significantly and negatively related to ecosystem productivity. Cumulatively, these four chapters advance our understanding of the connections between communities and ecosystems in a rapidly changing ecosystem.