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Article

The free troposphere is the location of important weather and climate processes. Here, horizontal and vertical transport of energy, mass, and momentum take place, and it holds greenhouse gases, water vapor, and clouds. The free troposphere therefore plays an important role in global climate feedback processes. Mountains provide important ecosystem services for a large lowland population. Mountain ecosystems may react particularly strongly to climatic changes. This is because mountains intersect important environmental and geoecological boundaries such as the snow line and the tree line. In a changing climate, these boundaries may shift. Climate change thus affects mountain glaciers, water resources, and mountain ecosystems. Climates of mountains and of the free troposphere have attracted scientists of the enlightenment and have been studied scientifically at least since the 18th century. High-altitude observatories were installed in the late 19th century, and upper-air measurements were started soon afterwards. However, even in the early 21st century, the climate observing systems do not well cover mountain regions and specifically mountain peaks. The temperature of the free troposphere is dominated by horizontal and vertical transport of sensible and latent heat, condensation and release of latent heat, and radiation to space. Mountain peaks sometimes reach into the free troposphere, but at the same time also share characteristics of surface climate. They are strongly influenced by radiative processes of the surrounding surface, while during the day they are often within the atmospheric boundary layer. With respect to climate change, temperature trends are amplified in the tropical upper-troposphere relative to the surface due to latent heat release, while in the Arctic the surface warms faster than the free atmosphere due to strong inversions and due to feedback processes operating at the surface. Mountain peaks may see both types of amplification. Several processes have been suggested to cause an elevation dependent warming, the most important of which arguably is the snow-albedo feedback. Elevation dependent warming is also seen in model studies and in observations, although detecting this signal in observations turns out rather difficult outside the tropics due to high variability and sometimes low-data quality. The observed climatic changes are expected to continue into the future.

Article

Climate change politics refers to attempts to define climate change as a physical phenomenon as well as to delineate and predict current and future effects on the environment and broader implications for human affairs as a foundation for political action. Defining the causes, scale, time frame, and consequences of climate change is critical to determining the political response. Given the high stakes involved in both the consequences of climate change and the distributive implications of policies to address it, climate change politics has been and remains highly contentious both within and across countries. Climate politics presents difficulties for study given its interdisciplinary nature and the scientific complexities involved in climate change. Climate change politics emerged in the mid- to late 1980s, as climate science became more accessible to policymakers and the public. However, scholarship on international climate politics was relatively slow to develop. Prior to 2008, major publications on international relations (except for policy journals) only lightly touched upon climate politics. Climate change was frequently referenced in articles on a range of topics, but it was not the primary focus of analysis. Since 2008 there has been a dramatic increase in literature focusing on climate change. The possibility of massive economic, political, and ecological dislocation from the consequences of climate change as well as from policies to address the problem have resulted in an extensive literature. Scholars have addressed aspects of climate politics from every paradigm within international relations, as well as drawing on research from numerous related disciplines. The international relations theories that shaped the scholarship on climate politics provide the foundation for understanding the ongoing normative debates surrounding domestic and international policies to address climate change.

Article

Debbie Hopkins and Ezra M. Markowitz

Despite scientific consensus on the anthropogenic causation of climate change, and ever-growing knowledge on the biophysical impacts of climate change, there is large variability in public perceptions of and belief in climate change. Public support for national and international climate policy has a strong positive association with certainty that climate change is occurring, human caused, serious, and solvable. Thus to achieve greater acceptance of national climate policy and international agreements, it is important to raise public belief in climate change and understandings of personal climate risk. Public understandings of climate change and associated risk perceptions have received significant academic attention. This research has been conducted across a range of spatial scales, with particular attention on large-scale, nationally representative surveys to gain insights into country-scale perceptions of climate change. Generalizability of nationally representative surveys allows some degree of national comparison; however, the ability to conduct such comparisons has been limited by the availability of comparative data sets. Consequently, empirical insights have been geographically biased toward Europe and North America, with less understanding of public perceptions of climate change in other geographical settings including the Global South. Moreover, a focus on quantitative surveying techniques can overlook the more nuanced, culturally determined factors that contribute to the construction of climate change perceptions. The physical and human geographies of climate change are diverse. This is due to the complex spatial dimensions of climate change and includes both the observed and anticipated geographical differentiation in risks, impacts, and vulnerabilities. While country location and national climate can impact upon how climate change is understood, so too will sociocultural factors such as national identity and culture(s). Studies have reported high variability in climate change perceptions, the result of a complex interplay between personal experiences of climate, social norms, and worldviews. Exploring the development of national-scale analyses and their findings over time, and the comparability of national data sets, may provide some insights into the factors that influence public perceptions of climate change and identify national-scale interventions and communications to raise risk perception and understanding of climate change.

Article

Confidence in the projected impacts of climate change on agricultural systems has increased substantially since the first Intergovernmental Panel on Climate Change (IPCC) reports. In Africa, much work has gone into downscaling global climate models to understand regional impacts, but there remains a dearth of local level understanding of impacts and communities’ capacity to adapt. It is well understood that Africa is vulnerable to climate change, not only because of its high exposure to climate change, but also because many African communities lack the capacity to respond or adapt to the impacts of climate change. Warming trends have already become evident across the continent, and it is likely that the continent’s 2000 mean annual temperature change will exceed +2°C by 2100. Added to this warming trend, changes in precipitation patterns are also of concern: Even if rainfall remains constant, due to increasing temperatures, existing water stress will be amplified, putting even more pressure on agricultural systems, especially in semiarid areas. In general, high temperatures and changes in rainfall patterns are likely to reduce cereal crop productivity, and new evidence is emerging that high-value perennial crops will also be negatively impacted by rising temperatures. Pressures from pests, weeds, and diseases are also expected to increase, with detrimental effects on crops and livestock. Much of African agriculture’s vulnerability to climate change lies in the fact that its agricultural systems remain largely rain-fed and underdeveloped, as the majority of Africa’s farmers are small-scale farmers with few financial resources, limited access to infrastructure, and disparate access to information. At the same time, as these systems are highly reliant on their environment, and farmers are dependent on farming for their livelihoods, their diversity, context specificity, and the existence of generations of traditional knowledge offer elements of resilience in the face of climate change. Overall, however, the combination of climatic and nonclimatic drivers and stressors will exacerbate the vulnerability of Africa’s agricultural systems to climate change, but the impacts will not be universally felt. Climate change will impact farmers and their agricultural systems in different ways, and adapting to these impacts will need to be context-specific. Current adaptation efforts on the continent are increasing across the continent, but it is expected that in the long term these will be insufficient in enabling communities to cope with the changes due to longer-term climate change. African famers are increasingly adopting a variety of conservation and agroecological practices such as agroforestry, contouring, terracing, mulching, and no-till. These practices have the twin benefits of lowering carbon emissions while adapting to climate change as well as broadening the sources of livelihoods for poor farmers, but there are constraints to their widespread adoption. These challenges vary from insecure land tenure to difficulties with knowledge-sharing. While African agriculture faces exposure to climate change as well as broader socioeconomic and political challenges, many of its diverse agricultural systems remain resilient. As the continent with the highest population growth rate, rapid urbanization trends, and rising GDP in many countries, Africa’s agricultural systems will need to become adaptive to more than just climate change as the uncertainties of the 21st century unfold.

Article

The reconstruction of climate in Poland in the past millennium, as measured by several kinds of proxy data, is more complete than that of many other regions in Europe and the world. In fact, the methods of climate reconstruction used here are commonly utilized for other regions. Proxy data available for Poland (whether by documentary, biological, or geothermal evidence) mainly allow for reconstructions of three meteorological variables: air temperature, ground-surface temperature, and precipitation. It must be underlined however, that air temperature reconstructions are possible only for certain times of the year. This is particularly characteristic of biological proxies (e.g., tree rings measure January–April temperature, chironomids provide data for August temperature, chrysophyte cysts identify cold seasons, etc.). Potentially, such limitation has no corresponding documentary evidence. In Poland these data are available only for climate reconstructions covering mainly the last 500 years because the number of historical sources pre-1500 is usually too small. Geothermal data allow for reconstruction of mean annual ground surface temperature generally for the last 500 years. Reconstructions of air temperature that cover the entire, or almost the entire, millennium and have high time resolution are only available from biological proxies (tree rings, chironomids, diatoms, etc.). At present, the best source of information about climate in Poland in the last millennium is still documentary evidence. This evidence defines a Medieval Warm Period (MWP), which was present in the 11th century and probably ended in the 14th or early 15th century. Air temperature in the MWP was probably about 0.5–1.0°C warmer than contemporary conditions on average, and the climate was characterized by the greatest degree of oceanity throughout the entire millennium. A Little Ice Age (LIA) can be also distinguished in Poland’s climate history. Data show that it clearly began around the mid-16th century and probably ended in the second half of the 19th century. In this LIA, winters were 1.5–3.0°C colder than present conditions, while summers tended to be warmer by about 0.5°C. As a result, the continentality of the climate in the LIA was the greatest for the entire millennium. Mean annual air temperature was probably lower than the modern temperature by about 0.9–1.5°C. The average rise of air temperature since the mid-19th century, which is often called the Contemporary Warming Period (CWP), is equal to about 1°C and is in line with the results of reconstructions using geothermal and dendrochronological methods. The reconstruction of precipitation in Poland is much more uncertain than the reconstruction of air temperature. There was probably considerably higher average precipitation in the 12th century (and particularly in the second half of this century), in the first half of the 16th century, and also in the first half of the 18th century. The second half of the 13th century and the first half of the 19th century were drier than average. In other periods, precipitation conditions were close to average, including for the entire CWP period.

Article

Tropical cyclones (TCs) in their most intense expression (hurricanes or typhoons) are the main natural hazards known to humankind. The impressive socioeconomic consequences for countries dealing with TCs make our ability to model these organized convective structures a key issue to better understanding their nature and their interaction with the climate system. The destructive effects of TCs are mainly caused by three factors: strong wind, storm surge, and extreme precipitation. These TC-induced effects contribute to the annual worldwide damage of the order of billions of dollars and a death toll of thousands of people. Together with the development of tools able to simulate TCs, an accurate estimate of the impact of global warming on TC activity is thus not only of academic interest but also has important implications from a societal and economic point of view. The aim of this article is to provide a description of the TC modeling implementations available to investigate present and future climate scenarios. The two main approaches to dynamically model TCs under a climate perspective are through hurricane models and climate models. Both classes of models evaluate the numerical equations governing the climate system. A hurricane model is an objective tool, designed to simulate the behavior of a tropical cyclone representing the detailed time evolution of the vortex. Considering the global scale, a climate model can be an atmosphere (or ocean)-only general circulation model (GCM) or a fully coupled general circulation model (CGCM). To improve the ability of a climate model in representing small-scale features, instead of a general circulation model, a regional model (RM) can be used: this approach makes it possible to increase the spatial resolution, reducing the extension of the domain considered. In order to be able to represent the tropical cyclone structure, a climate model needs a sufficiently high horizontal resolution (of the order of tens of kilometers) leading to the usage of a great deal of computational power. Both tools can be used to evaluate TC behavior under different climate conditions. The added value of a climate model is its ability to represent the interplay of TCs with the climate system, namely two-way relationships with both atmosphere and ocean dynamics and thermodynamics. In particular, CGCMs are able to take into account the well-known feedback between atmosphere and ocean components induced by TC activity and also the TC–related remote impacts on large-scale atmospheric circulation. The science surrounding TCs has developed in parallel with the increasing complexity of the mentioned tools, both in terms of progress in explaining the physical processes involved and the increased availability of computational power. Many climate research groups around the world, dealing with such numerical models, continuously provide data sets to the scientific community, feeding this branch of climate change science.

Article

Throughout the world, major climate-related catastrophic events have devastated lives and livelihoods. These events are predicted to increase in frequency and intensity across the globe, as greenhouse gas emissions continue to accumulate in our atmosphere. The causes and consequences of these disasters are not constrained to geographic and political boundaries, or even temporal scales, increasing the complexity of their management. Differences in cultures, governance and policy processes often occur among jurisdictions in a transboundary setting, whether adjacent nations that are exposed to the same transboundary hazard or across municipalities located within the same political jurisdiction. Political institutions and processes may vary across jurisdictions in a region, presenting challenges to cooperation and coordination of risk management. With shifting climates, risks from climate-related natural hazards are in constant flux, increasing the difficulty of making predictions about and governing these risks. Further, different groups of individuals may be exposed to the same climate hazard, but that exposure may affect these groups in unique ways. Managing climate change as a transboundary natural hazard may mandate a shift from a focus on individual climate risks to developing capacity to encourage learning from and adaptation to a diversity of climatic risks that span boundaries. Potential barriers to adaptation to climate risks must not be considered individually but rather as a part of a more dynamic system in which multiple barriers may interact, impeding effective management. Greater coordination horizontally, for example through networks linking cities, and vertically, across multiple levels of governance (e.g., local, regional, national, global), may aid in the development of increased capacity to deal with these transboundary risks. Greater public engagement in management of risks from climate change hazards, both in risk mitigation and post-hazard recovery, could increase local-level capacity to adapt to these hazards.

Article

The warming of the global climate is expected to continue in the 21st century, although the magnitude of change depends on future anthropogenic greenhouse gas emissions and the sensitivity of climate to them. The regional characteristics and impacts of future climate change in the Baltic Sea countries have been explored since at least the 1990s. Later research has supported many findings from the early studies, but advances in understanding and improved modeling tools have made the picture gradually more comprehensive and more detailed. Nevertheless, many uncertainties still remain. In the Baltic Sea region, warming is likely to exceed its global average, particularly in winter and in the northern parts of the area. The warming will be accompanied by a general increase in winter precipitation, but in summer, precipitation may either increase or decrease, with a larger chance of drying in the southern than in the northern parts of the region. Despite the increase in winter precipitation, the amount of snow is generally expected to decrease, as a smaller fraction of the precipitation falls as snow and midwinter snowmelt episodes become more common. Changes in windiness are very uncertain, although most projections suggest a slight increase in average wind speed over the Baltic Sea. Climatic extremes are also projected to change, but some of the changes will differ from the corresponding change in mean climate. For example, the lowest winter temperatures are expected to warm even more than the winter mean temperature, and short-term summer precipitation extremes are likely to become more severe, even in the areas where the mean summer precipitation does not increase. The projected atmospheric changes will be accompanied by an increase in Baltic Sea water temperature, reduced ice cover, and, according to most studies, reduced salinity due to increased precipitation and river runoff. The seasonal cycle of runoff will be modified by changes in precipitation and earlier snowmelt. Global-scale sea level rise also will affect the Baltic Sea, but will be counteracted by glacial isostatic adjustment. According to most projections, in the northern parts of the Baltic Sea, the latter will still dominate, leading to a continued, although decelerated, decrease in relative sea level. The changes in the physical environment and climate will have a number of environmental impacts on, for example, atmospheric chemistry, freshwater and marine biogeochemistry, ecosystems, and coastal erosion. However, future environmental change in the region will be affected by several interrelated factors. Climate change is only one of them, and in many cases its effects may be exceeded by other anthropogenic changes.

Article

Accurate projections of climate change under increasing atmospheric greenhouse gas levels are needed to evaluate the environmental cost of anthropogenic emissions, and to guide mitigation efforts. These projections are nowhere more important than Africa, with its high dependence on rain-fed agriculture and, in many regions, limited resources for adaptation. Climate models provide our best method for climate prediction but there are uncertainties in projections, especially on regional space scale. In Africa, limitations of observational networks add to this uncertainty since a crucial step in improving model projections is comparisons with observations. Exceeding uncertainties associated with climate model simulation are uncertainties due to projections of future emissions of CO2 and other greenhouse gases. Humanity’s choices in emissions pathways will have profound effects on climate, especially after the mid-century. The African Sahel is a transition zone characterized by strong meridional precipitation and temperature gradients. Over West Africa, the Sahel marks the northernmost extent of the West African monsoon system. The region’s climate is known to be sensitive to sea surface temperatures, both regional and global, as well as to land surface conditions. Increasing atmospheric greenhouse gases are already causing amplified warming over the Sahara Desert and, consequently, increased rainfall in parts of the Sahel. Climate model projections indicate that much of this increased rainfall will be delivered in the form of more intense storm systems. The complicated and highly regional precipitation regimes of East Africa present a challenge for climate modeling. Within roughly 5º of latitude of the equator, rainfall is delivered in two seasons—the long rains in the spring, and the short rains in the fall. Regional climate model projections suggest that the long rains will weaken under greenhouse gas forcing, and the short rains season will extend farther into the winter months. Observations indicate that the long rains are already weakening. Changes in seasonal rainfall over parts of subtropical southern Africa are observed, with repercussions and challenges for agriculture and water availability. Some elements of these observed changes are captured in model simulations of greenhouse gas-induced climate change, especially an early demise of the rainy season. The projected changes are quite regional, however, and more high-resolution study is needed. In addition, there has been very limited study of climate change in the Congo Basin and across northern Africa. Continued efforts to understand and predict climate using higher-resolution simulation must be sustained to better understand observed and projected changes in the physical processes that support African precipitation systems as well as the teleconnections that communicate remote forcings into the continent.

Article

Climate politics presents difficulties for study given its interdisciplinary nature and the scientific complexities involved in climate change. Climate change politics had got its start in the mid- to late 1980s, as climate science became more and more accessible to policy makers and the general public. Yet prior to 2008, climate politics was only touched upon in major publications on international relations, with the exception of policy journals. Climate change was frequently referenced in articles on a range of topics, but it was not the primary focus of analysis. The recent years have seen an explosion in literature focusing on the topic, however. The potential for massive economic, political, and ecological dislocation from the consequences of climate change as well as from the potential policies to address the problem have since resulted in an extensive literature, with scholars addressing aspects of climate politics from every paradigm within international relations, as well as drawing on research in numerous other related disciplines. In addition, efforts to address the consequences of climate change have evoked controversial ethical and distributive justice questions that have produced an important normative literature. Overall, the literature on climate politics centers on two issues: how we can explain the international political response to climate change, as well as how the international community should respond to climate change.

Article

Climate change politics refers to attempts to define climate change as a physical phenomenon as well as to delineate current and predict future effects on the environment and broader implications for human affairs as a foundation for political action. Defining the causes, scale, time frame, and consequences of climate change is critical to determining the political response. Given the high stakes involved in both the consequences of climate change and the distributive implications of policies to address climate change, climate change politics has been and remains highly contentious both within countries and across countries. Climate politics presents difficulties for study given its interdisciplinary nature and the scientific complexities involved in climate change. The international relations literature surrounding climate politics has also evolved and grown substantially since the mid-2000s. Efforts to address the consequences of climate change have evoked controversial ethical and distributive justice questions that have produced an important normative literature. These debates increasingly inform the ongoing negotiations surrounding responsibility for the problem of climate change and the policies required to address climate change. There is also a larger debate regarding the complex linkages between climate change and broader ecological as well as economic and political consequences of both the effects of climate change and policies designed to reduce greenhouse gas emissions or remove them from the atmosphere. As we enter the 2020s, a new debate has emerged related to the implications of the posited transition to the Anthropocene Epoch and the future of climate politics. Normative and policy debates surrounding climate change politics remain contentious without a clear path to meaningful political action.

Article

Christopher Shaw

International climate negotiations seek to limit warming to an average of two degrees Celsius (2°C). This objective is justified by the claim that scientists have identified two degrees of warming as the point at which climate change becomes dangerous. Climate scientists themselves maintain that while science can provide projections of possible impacts at different levels of warming, determining what constitutes an acceptable level of risk is not a matter to be decided by science alone, but is a value choice to be deliberated upon by societies as a whole. Hence, while climate science can inform debates about how much warming is too much, it cannot provide a definitive answer to that question. In order to fully understand how climate change came to be defined as a phenomenon with a single global dangerous limit of 2°C, it is necessary to incorporate insights from the social sciences. Political economy, culture, economics, sociology, geography, and social psychology have all played a role in defining what constitutes an acceptable level of climate risk. These perspectives can be applied through the framework of institutional analysis to examine reports from the Intergovernmental Panel on Climate Change and other international organizations. This interdisciplinary approach offers the potential to provide a comprehensive history of how climate science has been interpreted in policy making. An interdisciplinary analysis is also essential in order to move beyond historical description to provide a narrative of considerable explanatory power. Such insights offer a valuable framework for considering current debates about whether or not it will be possible to limit warming to 2°C.

Article

Jill E. Hopke and Luis E. Hestres

Divestment is a socially responsible investing tactic to remove assets from a sector or industry based on moral objections to its business practices. It has historical roots in the anti-apartheid movement in South Africa. The early-21st-century fossil fuel divestment movement began with climate activist and 350.org co-founder Bill McKibben’s Rolling Stone article, “Global Warming’s Terrifying New Math.” McKibben’s argument centers on three numbers. The first is 2°C, the international target for limiting global warming that was agreed upon at the United Nations Framework Convention on Climate Change 2009 Copenhagen conference of parties (COP). The second is 565 Gigatons, the estimated upper limit of carbon dioxide that the world population can put into the atmosphere and reasonably expect to stay below 2°C. The third number is 2,795 Gigatons, which is the amount of proven fossil fuel reserves. That the amount of proven reserves is five times that which is allowable within the 2°C limit forms the basis for calls to divest. The aggregation of individual divestment campaigns constitutes a movement with shared goals. Divestment can also function as “tactic” to indirectly apply pressure to targets of a movement, such as in the case of the movement to stop the Dakota Access Pipeline in the United States. Since 2012, the fossil fuel divestment movement has been gaining traction, first in the United States and United Kingdom, with student-led organizing focused on pressuring universities to divest endowment assets on moral grounds. In partnership with 350.org, The Guardian launched its Keep it in the Ground campaign in March 2015 at the behest of outgoing editor-in-chief Alan Rusbridger. Within its first year, the digital campaign garnered support from more than a quarter-million online petitioners and won a “campaign of the year” award in the Press Gazette’s British Journalism Awards. Since the launch of The Guardian’s campaign, “keep it in the ground” has become a dominant frame used by fossil fuel divestment activists. Divestment campaigns seek to stigmatize the fossil fuel industry. The rationale for divestment rests on the idea that fossil fuel companies are financially valued based on their resource reserves and will not be able to extract these reserves with a 2°C or lower climate target. Thus, their valuation will be reduced and the financial holdings become “stranded assets.” Critics of divestment have cited the costs and risks to institutional endowments that divestment would entail, arguing that to divest would go against their fiduciary responsibility. Critics have also argued that divesting from fossil fuel assets would have little or no impact on the industry. Some higher education institutions, including Princeton and Harvard, have objected to divestment as a politicization of their endowments. Divestment advocates have responded to this concern by pointing out that not divesting is not a politically neutral act—it is, in fact, choosing the side of fossil fuel corporations.

Article

Catrien Termeer, Arwin van Buuren, Art Dewulf, Dave Huitema, Heleen Mees, Sander Meijerink, and Marleen van Rijswick

Adaptation to climate change is not only a technical issue; above all, it is a matter of governance. Governance is more than government and includes the totality of interactions in which public as well as private actors participate, aiming to solve societal problems. Adaptation governance poses some specific, demanding challenges, such as the context of institutional fragmentation, as climate change involves almost all policy domains and governance levels; the persistent uncertainties about the nature and scale of risks and proposed solutions; and the need to make short-term policies based on long-term projections. Furthermore, adaptation is an emerging policy field with, at least for the time being, only weakly defined ambitions, responsibilities, procedures, routines, and solutions. Many scholars have already shown that complex problems, such as adaptation to climate change, cannot be solved in a straightforward way with actions taken by a hierarchic or monocentric form of governance. This raises the question of how to develop governance arrangements that contribute to realizing adaptation options and increasing the adaptive capacity of society. A series of seven basic elements have to be addressed in designing climate adaptation governance arrangements: the framing of the problem, the level(s) at which to act, the alignment across sectoral boundaries, the timing of the policies, the selection of policy instruments, the organization of the science-policy interface, and the most appropriate form of leadership. For each of these elements, this chapter suggests some tentative design principles. In addition to effectiveness and legitimacy, resilience is an important criterion for evaluating these arrangements. The development of governance arrangements is always context- and time-specific, and constrained by the formal and informal rules of existing institutions.

Article

The contribution summarizes the topic of climate change communication in Switzerland. The development of the topic of “climate change” is described and located within the general area of environmental politics in Switzerland, based on the specifics of Switzerland as a small, federal state, and non-EU member with direct democratic political processes. Climate change communication then is analyzed based on the results of several content analyses, mostly of Swiss print media, which focus on intensity of coverage, topics, and media frames. In the last part, the perception of and attitudes towards environment and climate change are presented and compared to other countries, based on public opinion survey data.

Article

Anil Markandya, Elena Paglialunga, Valeria Costantini, and Giorgia Sforna

Economic damage from climate change includes several aspects that need to be considered at the global and regional levels to achieve an equitable common solution to global warming. The economic literature reviewed here analyzes this issue under three general perspectives. First, the analytical estimation of the linkages between damages in monetary terms and climate variables, as projections of temperature, precipitation, and frequency of extreme events, is rapidly evolving. Damage functions are included in complex economic models in order to calculate the economic impact of the climate change on economic output and growth, thus informing the debate on the amount of resources that should be devoted to reducing greenhouse gas (GHG) emissions and limiting climate damages. The choice of the geographical aggregation in this respect is a crucial aspect to be considered if policy advice is to be formulated on the basis of model results. The higher the level of regional detail, the more reliable the results are in terms of geographical distribution of economic damages. Second, the precise estimation of the costs associated with different damages caused by climate change is attracting growing interest. Climate costs present a wide range of heterogeneity for several reasons, such as the different formulation of the damage function adopted, the modeling design of the economic impact, the temporal horizon considered, and the differentiation across sectors. Two broad categories of analysis are relevant. The first refers to the choice of the sectoral dimension under investigation, where some studies cover multiple sectors and their interactions, while others analyze specific sectors in depth. The second classification criterion refers to the choice of the economic aspects estimated, where a strand of literature analyzes only market-based costs, while other analyses also include non-market (or intangible) damages. The most common sectors investigated are agriculture, forestry, health, energy, coastal zones and sea level rise, extreme events, tourism, ecosystem, industry, air quality, and catastrophic damages. Most studies consider market-based costs, while non-market impacts need to be better detailed in economic models. Third, the computation of a single number through the analytical framework of the social costs of carbon (SCC) represents a key aspect of the process of adapting complex results in order to properly inform the political debate. SCC represents the marginal global damage cost of carbon emissions and can also be interpreted as the economic value of damages avoided for unitary GHG emission reduction. Several uncertainties still influence the robustness of the SCC analytical framework, such as the choice of the discount rate, which strongly influences the role of SCC in supporting or not mitigation action in the short term. Although the debate on the economic damages arising from climate change is flourishing, several aspects still need to be investigated in order to build a common consensus within the scientific community as a necessary condition to properly inform the political debate and to facilitate the achievement of a long-term equitable global climate agreement.

Article

Climate and carbon cycle are tightly coupled on many time scales, from the interannual to the multimillennial. Observation always shows a positive feedback between climate and the carbon cycle: elevated atmospheric CO2 leads to warming, but warming is expected to further release of carbon to the atmosphere, enhancing the atmospheric CO2 increase. Earth system models do represent these climate–carbon cycle feedbacks, always simulating a positive feedback over the 21st century; that is, climate change will lead to loss of carbon from the land and ocean reservoirs. These processes partially offset the increases in land and ocean carbon sinks caused by rising atmospheric CO2. As a result, more of the emitted anthropogenic CO2 will remain in the atmosphere. There is, however, a large uncertainty on the magnitude of this feedback. Recent studies now help to reduce this uncertainty. On short, interannual, time scales, El Niño years record larger-than-average atmospheric CO2 growth rate, with tropical land ecosystems being the main drivers. These climate–carbon cycle anomalies can be used as emerging constraint on the tropical land carbon response to future climate change. On a longer, centennial, time scale, the variability of atmospheric CO2 found in records of the last millennium can be used to constrain the overall global carbon cycle response to climate. These independent methods confirm that the climate–carbon cycle feedback is positive, but probably more consistent with the lower end of the comprehensive models range, excluding very large climate–carbon cycle feedbacks.

Article

Bruno Takahashi and Alejandra Martinez

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

Article

Rasmus Benestad

The Barents Sea is a region of the Arctic Ocean named after one of its first known explorers (1594–1597), Willem Barentsz from the Netherlands, although there are accounts of earlier explorations: the Norwegian seafarer Ottar rounded the northern tip of Europe and explored the Barents and White Seas between 870 and 890 ce, a journey followed by a number of Norsemen; Pomors hunted seals and walruses in the region; and Novgorodian merchants engaged in the fur trade. These seafarers were probably the first to accumulate knowledge about the nature of sea ice in the Barents region; however, scientific expeditions and the exploration of the climate of the region had to wait until the invention and employment of scientific instruments such as the thermometer and barometer. Most of the early exploration involved mapping the land and the sea ice and making geographical observations. There were also many unsuccessful attempts to use the Northeast Passage to reach the Bering Strait. The first scientific expeditions involved F. P. Litke (1821±1824), P. K. Pakhtusov (1834±1835), A. K. Tsivol’ka (1837±1839), and Henrik Mohn (1876–1878), who recorded oceanographic, ice, and meteorological conditions. The scientific study of the Barents region and its climate has been spearheaded by a number of campaigns. There were four generations of the International Polar Year (IPY): 1882–1883, 1932–1933, 1957–1958, and 2007–2008. A British polar campaign was launched in July 1945 with Antarctic operations administered by the Colonial Office, renamed as the Falkland Islands Dependencies Survey (FIDS); it included a scientific bureau by 1950. It was rebranded as the British Antarctic Survey (BAS) in 1962 (British Antarctic Survey History leaflet). While BAS had its initial emphasis on the Antarctic, it has also been involved in science projects in the Barents region. The most dedicated mission to the Arctic and the Barents region has been the Arctic Monitoring and Assessment Programme (AMAP), which has commissioned a series of reports on the Arctic climate: the Arctic Climate Impact Assessment (ACIA) report, the Snow Water Ice and Permafrost in the Arctic (SWIPA) report, and the Adaptive Actions in a Changing Arctic (AACA) report. The climate of the Barents Sea is strongly influenced by the warm waters from the Norwegian current bringing heat from the subtropical North Atlantic. The region is 10°C–15°C warmer than the average temperature on the same latitude, and a large part of the Barents Sea is open water even in winter. It is roughly bounded by the Svalbard archipelago, northern Fennoscandia, the Kanin Peninsula, Kolguyev Island, Novaya Zemlya, and Franz Josef Land, and is a shallow ocean basin which constrains physical processes such as currents and convection. To the west, the Greenland Sea forms a buffer region with some of the strongest temperature gradients on earth between Iceland and Greenland. The combination of a strong temperature gradient and westerlies influences air pressure, wind patterns, and storm tracks. The strong temperature contrast between sea ice and open water in the northern part sets the stage for polar lows, as well as heat and moisture exchange between ocean and atmosphere. Glaciers on the Arctic islands generate icebergs, which may drift in the Barents Sea subject to wind and ocean currents. The land encircling the Barents Sea includes regions with permafrost and tundra. Precipitation comes mainly from synoptic storms and weather fronts; it falls as snow in the winter and rain in the summer. The land area is snow-covered in winter, and rivers in the region drain the rainwater and meltwater into the Barents Sea. Pronounced natural variations in the seasonal weather statistics can be linked to variations in the polar jet stream and Rossby waves, which result in a clustering of storm activity, blocking high-pressure systems. The Barents region is subject to rapid climate change due to a “polar amplification,” and observations from Svalbard suggest that the past warming trend ranks among the strongest recorded on earth. The regional change is reinforced by a number of feedback effects, such as receding sea-ice cover and influx of mild moist air from the south.

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Despite an accumulation of scientific evidence on both the causes and consequences of climate change, U.S. public opinion on the subject has splintered sharply along party lines. While a vast majority of Democrats now believe that global warming is real, that its effects will happen within their lifetime, and that human activity is the dominant cause, Republicans have grown increasingly skeptical, creating a yawning gap that complicates efforts to communicate the urgency of the problem and the need for aggressive action. When attitudes harden and diverge, it is often driven by the behavior of political elites, who shape the frames and mental models that people use to interpret events. Scholars have long observed that people resort instinctively to heuristics to ease the burden of making decisions, especially on issues like climate, where there is an obvious disconnect between scientific understanding and mass competence. Those cues, however, are often unreliable and prone to cognitive bias. When voters act upon signals provided by their preferred political party and by selective exposure to preferred media outlets, they may do so mechanically, with little regard for the accuracy of the evidence that they receive, or they may ignore and distort information in a way that reinforces preexisting assumptions. In the end, beliefs about climate change are as complex as the issue itself, which suggests that awareness of the problem and an understanding of its effects will not translate automatically—or even easily—into increased concern, issue salience, or policy preferences. The “pictures in our heads,” to borrow Walter Lippmann’s famous phrase, are shaped less by factual knowledge than by a variety of other factors more difficult to control—by personal experience and assorted real-world cues (such as the weather), but also by opinion leaders, media narratives, and political rhetoric, each of which provides a competing frame of reference with the power to filter and mislead. Because climate change has become so heavily laden with values and so absorbed into partisan identity, it will be nearly impossible to build social consensus through conventional means. Once a “hard” issue for all, which seemed to demand sophisticated calculation or technical expertise, it has now become an “easy” one for many, where the reactions that it prompts are familiar, stable, and symbolic, increasingly polarized, immune to rational argument, and vulnerable to manipulation by elites.