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Jonathan Holmes and Philipp Hoelzmann
From the end of the last glacial stage until the mid-Holocene, large areas of arid and semi-arid North Africa were much wetter than present, during the interval that is known as the African Humid Period (AHP). During this time, large areas were characterized by a marked increase in precipitation, an expansion of lakes, river systems, and wetlands, and the spread of grassland, shrub land, and woodland vegetation into areas that are currently much drier. Simulations with climate models indicate that the AHP was the result of orbitally forced increase in northern hemisphere summer insolation, which caused the intensification and northward expansion of the boreal summer monsoon. However, feedbacks from ocean circulation, land-surface cover, and greenhouse gases were probably also important.
Lake basins and their sediment archives have provided important information about climate during the AHP, including the overall increases in precipitation and in rates, trajectories, and spatial variations in change at the beginning and the end of the interval. The general pattern is one of apparently synchronous onset of the AHP at the start of the Bølling-Allerød interstadial around 14,700 years ago, although wet conditions were interrupted by aridity during the Younger Dryas stadial. Wetter conditions returned at the start of the Holocene around 11,700 years ago covering much of North Africa and extended into parts of the southern hemisphere, including southeastern Equatorial Africa. During this time, the expansion of lakes and of grassland or shrub land vegetation over the area that is now the Sahara desert, was especially marked. Increasing aridity through the mid-Holocene, associated with a reduction in northern hemisphere summer insolation, brought about the end of the AHP by around 5000–4000 years before present. The degree to which this end was abrupt or gradual and geographically synchronous or time transgressive, remains open to debate. Taken as a whole, the lake sediment records do not support rapid and synchronous declines in precipitation and vegetation across the whole of North Africa, as some model experiments and other palaeoclimate archives have suggested. Lake sediments from basins that desiccated during the mid-Holocene may have been deflated, thus providing a misleading picture of rapid change. Moreover, different proxies of climate or environment may respond in contrasting ways to the same changes in climate. Despite this, there is evidence of rapid (within a few hundred years) termination to the AHP in some regions, with clear signs of a time-transgressive response both north to south and east to west, pointing to complex controls over the mid-Holocene drying of North Africa.
Courtney Plante, Johnie J. Allen, and Craig A. Anderson
Given the dire nature of many researchers’ predictions about the effects of global climate change (e.g., rising sea levels, droughts, more extreme weather), it comes as little surprise that less attention has been paid to the subtler, less direct outcomes of rapid climate change: psychological, sociological, political, and economic effects. In this chapter we explore one such outcome in particular: the effects of rapid climate change on aggression. We begin by exploring the potential for climate change to directly affect aggression in individuals, focusing on research showing the relationship between uncomfortably hot ambient temperature and aggression. Next, we review several lines of research illustrating ways that climate change can indirectly increase aggression in individuals. We then shift our focus from individuals to the effects of climate change on group-level aggression. We finish by addressing points of contention, including the challenge that the effects of climate change on aggression are too remote and too small to be considered relevant.
Climate change is one of the most pressing issues facing humanity today. One reason is that, in recent years, it has moved from being a predominantly physical phenomenon to being simultaneously a political, social, and cultural phenomenon—and thus, a communication challenge. Current research shows that the meaning people ascribe to climate change is closely related to how it is portrayed during communication. Language plays a crucial role in this. Language not only reflects and expresses facts and observations but also influences attitudes and behavior. It helps to represent the reality but can also create new realities. In addition, the climate change debate is particularly multi-voiced, including both explicit and implicit or hidden voices representing different actors and interests. In order to know more about to what extent and in what way language matters, various linguistic and textual studies are undertaken: studies of words, of combinations of words, and of entire texts taken from different contexts, such as scientific reports, political documents, mainstream media, and new social media. Knowledge from linguistic and textual studies contributes to an improved knowledge base for societal and political actions to be undertaken in order to avoid dangerous consequences of climate change.
Jens Wolling and Dorothee Arlt
The annual climate summits (Conferences of the Parties, or COPs) are major political events that receive considerable media attention. In this way, the topic of climate change returns regularly to both the media and the political agenda. It makes sense, therefore, that communication research regards COPs as occasion to investigating how the media cover climate change. Nevertheless, this strategy has two shortcomings: On the one hand the focus on the conferences might provide a distorted picture—because of the political character of the conferences, the role of political actors and policy-related frames might be overestimated. On the other hand, the political character of the conferences is not always considered appropriately. Most research is mainly interested in the coverage on climate change in the context of the conferences and not in the political discussions taking place at the summits. Future research should address these discussions more intensively, giving more attention especially to the debates in the various online media.
Hans Peter Peters
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Climate Science. Please check back later for the full article.
Global climate change is one of the risks that have become known to the public and to decision makers only through scientific research. Climate scientists were the dominant communicators in the early climate-change discourse, putting the issue on the public agenda, and they remained important communicators in later discourse stages. Among the scientists visible in the mass media coverage on climate change are climate researchers as well as researchers from other disciplines dealing with technical or socioeconomic aspects of global climate-change mitigation and adaptation. Surveys among scientists involved in research on climate change and content analyses of media coverage on climate change show the widespread involvement of scientists in public communication and inform us about their communication-relevant beliefs, preferences, attitudes, and perception of their role as public communicators. Two theoretical perspectives can be used to understand the role of climate researchers as public communicators: medialization of science and specification of the “public expert” role in the science-policy context of climate change.
Peter Weingart’s medialization of science framework points to the media orientation of scientific communicators in the climate-change discourse. The medialization thesis assumes that scientists and scientific organizations have a strong interest in increasing their visibility and caring for their image in the media in order to build legitimacy and raise support for their demands and persuasive goals. The thesis further argues that scientists interested in public visibility tend to adjust their communication behavior and public messages to media expectations and also consider media criteria such as public attention and recognition when making decisions about research and scholarly communication. According to this thesis, the media orientation of science not only affects the public representation of science but also has repercussions for scientific inquiry, which threatens scientific autonomy and constitutes a risk to the quality of scientific knowledge.
The science-policy context of the public discourse on global climate change has important implications for scientists' role as public communicators. Whether or not they themselves recognize it, scientists in the climate-change discourse are not primarily involved as popularizers of their research but as “public experts” whose messages are received—and probably most often intended—as contributions to the understanding, assessment, and governance of risks resulting from global climate change. Scientists construe their expert role in different ways, however. One dimension of variation concerns the readiness of scientists in public communication to go beyond relatively certain facts and also offer interpretations, generalizations, or projections that are uncertain and may be controversial within science. A second dimension concerns its relation to decision making: assuming a guarded role as provider of reliable knowledge to inform opinion formation and decision making of (imagined) clients such as public or politics versus an advocacy role aiming at pushing public opinion and decisions into a particular direction. Some perceptions of the expert role conform more with traditional scientific norms of objectivity and responsibility than others.
Mental models are the sets of causal beliefs we “run” in our minds to infer what will happen in a given event or situation. Mental models, like other models, are useful simplifications most of the time. They can, however, lead to mistaken or misleading inferences, for example, if the analogies that inform them are misleading in some regard. The coherence and consistency of mental models a person employs to solve a given problem are a function of that person’s expertise. The less familiar and central a problem is, the less coherent and consistent the mental models brought to bear on that problem are likely to be. For problems such as those posed by anthropogenic climate change, most people are likely to recruit multiple mental models to make judgments and decisions.
Common types of mental models of climate change and global warming include: (a) a carbon emissions model, in which global warming is a result of burning fossil fuels thereby emitting CO2, and of deforestation, which both releases sequestered CO2 and decreases the possible sinks that might take CO2 out of the atmosphere; (b) a stratospheric ozone depletion mental model, which conflates stratospheric ozone depletion with global warming; (c) an air pollution mental model, in which global warming is viewed as air pollution; and (d) a weather change model, in which weather and climate are conflated. As social discourse around global warming and climate change has increased, mental models of climate change have become more complex, although not always more coherent. One such complexity is the belief that climate changes according to natural cycles and due to factors beyond human control, in addition to changes resulting from human activities such as burning fossil fuels and releasing other greenhouse gases.
As our inference engines, mental models play a central role in problem solving and subjective projections and are hence at the heart of risk perceptions and risk decision-making. However, both perceiving and making decisions about climate change and the risks thereof are affective and social processes foremost.
Methods for Assessing Journalistic Decisions, Advocacy Strategies, and Climate Change Communication Practices
Research in the field of journalistic decisions, advocacy strategies, and communication practices is very heterogeneous, comprising diverse groups of actors and research questions. Not surprisingly, various methods have been applied to assess actors’ motives, strategies, intentions, and communication behaviors. This article provides an overview of the most common methods applied—i.e., qualitative and quantitative approaches to textual analyses, interviewing techniques, observational and experimental research. After discussing the major strengths and weaknesses of each method, an outlook on future research is given. One challenge of the future study of climate change communication will be to account for its dynamics, with various actors reacting to one another in their public communication. To better approximate such dynamics in the future, more longitudinal research will be needed.
Visual representation has been important in communicating and constructing the environment as a focus for public and political concern since the rise of environmentalism in the 1960s. As communications media have themselves become increasingly visual with the rise of digital media, so too has visual communication become key to public debate about environmental issues, no more so than in public debate and the politics of climate change.
This chapter surveys the methods, approaches, and frameworks deployed in emerging research on public-mediated visual communication about climate change. Research on the visual mediation of climate change is itself part of the emerging field of visual environmental communication research, defined as research concerned with theorizing and empirically examining how visual imagery contributes to the increasingly multimodal public communication of the environment. Focused on a sociological understanding of the contribution that visuals make to the social, political, and cultural construction of “the environment,” visual environmental communication research analytically requires a multimodal approach, which situates analysis of the semiotic, discursive, rhetorical, and narrative characteristics of visuals in relation to the communicative, cultural, and historical contexts and in relation to the three main sites—production, content, and audiences/consumption—of communication in the public sphere.
Mineral dust is the most important natural aerosol type by mass, with northern Africa the most prominent source region worldwide. Dust particles are lifted into the atmosphere by strong winds over arid or semiarid soils through a range of emission mechanisms, the most important of which is saltation. Dust particles are mixed vertically by turbulent eddies in the desert boundary layer (up to 6km) or even higher by convective and frontal circulations. The meteorological systems that generate winds strong enough for dust mobilization cover scales from dust devils (~100m) to large dust outbreaks related to low- and high-pressure systems over subtropical northern Africa (thousands of kilometers) and include prominent atmospheric features such as the morning breakdown of low-level jets forming in the stable nighttime boundary layer and cold pools emanating from deep convective systems (so-called haboobs). Dust particles are transported in considerable amounts from northern Africa to remote regions such as the Americas and Europe. The removal of dust particles from the atmosphere occurs through gravitational settling, molecular and turbulent diffusion (dry deposition), as well as in-cloud and sub-cloud scavenging (wet deposition). Advances in satellite technology and numerical dust models (including operational weather prediction systems) have led to considerable progress in quantifying the temporal and spatial variability of dust from Africa, but large uncertainties remain for practically all stages of the dust cycle. The annual cycle of dustiness is dominated by the seasonal shift of rains associated with the West African monsoon and the Mediterranean storm track. In summer, maximum dust loadings are observed over Mauritania and Mali, and the main export is directed toward the Caribbean Sea, creating the so-called elevated Saharan Air Layer. In winter the northeasterly harmattan winds transport dust to the tropical Atlantic and across to southern America, usually in a shallower layer.
Mineral dust has a multitude of impacts on climate and weather systems but also on humans (air pollution, visibility, erosion). Nutrients contained in dust fertilize marine and terrestrial ecosystems and therefore impact the global carbon cycle. Dust affects the energy budget directly through interactions with short- and long-wave radiation, with details depending crucially on particle size, shape, and chemical composition. Mineral dust particles are the most important ice-nuclei worldwide and can also serve as condensation nuclei in liquid clouds, but details are not well understood. The resulting modifications to cloud characteristics and precipitation can again affect the energy (and water) budget. Complicated responses and feedbacks on atmospheric dynamics are known, including impacts on regional-scale circulations, sea-surface temperatures, surface fluxes and boundary layer mixing, vertical stability, near-surface winds, soil moisture, and vegetation (and therefore again dust emission). A prominent example of such complex interactions is the anti-correlation between African dust and Atlantic hurricane activity from weekly to decadal timescales, the causes of which remain difficult to disentangle. Particularly in the early 21st century, research on African dust intensified substantially and became more interdisciplinary, leading to some significant advances in our understanding of this fascinating and multifaceted element of the Earth system.
Yanhong Gao and Deliang Chen
The modeling of climate over the Tibetan Plateau (TP) started with the introduction of Global Climate Models (GCMs) in the 1950s. Since then, GCMs have been developed to simulate atmospheric dynamics and eventually the climate system. As the highest and widest international plateau, the strong orographic forcing caused by the TP and its impact on general circulation rather than regional climate was initially the focus. Later, with growing awareness of the incapability of GCMs to depict regional or local-scale atmospheric processes over the heterogeneous ground, coupled with the importance of this information for local decision-making, regional climate models (RCMs) were established in the 1970s. Dynamic and thermodynamic influences of the TP on the East and South Asia summer monsoon have since been widely investigated by model. Besides the heterogeneity in topography, impacts of land cover heterogeneity and change on regional climate were widely modeled through sensitivity experiments.
In recent decades, the TP has experienced a greater warming than the global average and those for similar latitudes. GCMs project a global pattern where the wet gets wetter and the dry gets drier. The climate regime over the TP covers the extreme arid regions from the northwest to the semi-humid region in the southeast. The increased warming over the TP compared to the global average raises a number of questions. What are the regional dryness/wetness changes over the TP? What is the mechanism of the responses of regional changes to global warming? To answer these questions, several dynamical downscaling models (DDMs) using RCMs focusing on the TP have recently been conducted and high-resolution data sets generated. All DDM studies demonstrated that this process-based approach, despite its limitations, can improve understandings of the processes that lead to precipitation on the TP. Observation and global land data assimilation systems both present more wetting in the northwestern arid/semi-arid regions than the southeastern humid/semi-humid regions. The DDM was found to better capture the observed elevation dependent warming over the TP. In addition, the long-term high-resolution climate simulation was found to better capture the spatial pattern of precipitation and P-E (precipitation minus evapotranspiration) changes than the best available global reanalysis. This facilitates new and substantial findings regarding the role of dynamical, thermodynamics, and transient eddies in P-E changes reflected in observed changes in major river basins fed by runoff from the TP. The DDM was found to add value regarding snowfall retrieval, precipitation frequency, and orographic precipitation.
Although these advantages in the DDM over the TP are evidenced, there are unavoidable facts to be aware of. Firstly, there are still many discrepancies that exist in the up-to-date models. Any uncertainty in the model’s physics or in the land information from remote sensing and the forcing could result in uncertainties in simulation results. Secondly, the question remains of what is the appropriate resolution for resolving the TP’s heterogeneity. Thirdly, it is a challenge to include human activities in the climate models, although this is deemed necessary for future earth science. All-embracing further efforts are expected to improve regional climate models over the TP.