61-80 of 247 Results

Article

Tim Rayner and Andrew Jordan

The European Union (EU) has long claimed, with some justification, to be a leader in international climate policy. Its policy activities in this area, dating from the early 1990s, have had enormous influence within and beyond Europe. The period since ca. 2000 in particular has witnessed the repeated emergence of policies and targets that are increasingly distinct from national ones and sometimes globally innovative. They encompass a wide array of instruments (e.g., market-based, informational, voluntary, as well as regulatory). Policy development has been motivated by a mixture of concerns: to avoid national differences in policy causing distortions of the EU’s internal market; to enhance the domestic legitimacy of the wider project of European integration; to improve energy security; and to increase economic competitiveness through “ecological modernization.” Climate policy has also offered a means to enhance the standing of the EU as a global actor. The EU has, in general, been influential in international negotiations, for example, in its promotion of the 2°C warming limit and advocacy of emission reduction “targets and timetables.” In turn, its own policy has been shaped by developments at global level, as with the surprisingly enthusiastic adoption of the “flexible mechanism” of emissions trading. However, it is becoming increasingly apparent that acute challenges to policy coherence and effectiveness—applying to emerging policy on adaptation, as well as mitigation—lie ahead in a Europe that is more polarized between its more environmentally conscious Member States and those in central and eastern Europe who have extracted significant concessions to protect their fossil fuel–intensive sectors. Although the Paris Agreement of 2015 offers an important opportunity to “ratchet up” the ambition of EU policy, it is proving to be a difficult one to seize.

Article

Philipp Pattberg and Oscar Widerberg

In 1992, when the international community agreed on the United Nations Framework Convention on Climate Change (UNFCCC), the science of climate change was under development, global greenhouse gas (GHG) emissions were by and large produced by developed countries, and the concentrations of CO2 in the atmosphere had just surpassed 350 ppm. Some 25 years later, climate change is scientifically uncontested, China has overtaken the United States as the world’s biggest emitter of CO2, and concentrations are now measured above 400 ppm. Against this background, states have successfully concluded a new global agreement under the UNFCCC, the 2015 Paris Agreement. Prior to the Paris Agreement, the climate regime focused on allocating emission reduction commitments among (a group of) countries. However, the new agreement has turned the climate regime on its feet by introducing an approach based on Nationally Determined Contributions (NDCs). Under this approach, states decide their ambition levels independently instead of engaging in negotiations about “who does what.” The result is a more flexible system that for the first time includes all countries in the quest to reduce GHG emissions to keep temperature increase below 2°C compared to preindustrial levels. Moreover, the international climate regime has transformed into a regime complex, denoting the broad activities of smaller groups of states as well as non-party actors, such as cities, regions, companies, and non-governmental organizations along with United Nations agencies.

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

Swadhin Behera and Toshio Yamagata

The El Niño Modoki/La Niña Modoki (ENSO Modoki) is a newly acknowledged face of ocean-atmosphere coupled variability in the tropical Pacific Ocean. The oceanic and atmospheric conditions associated with the El Niño Modoki are different from that of canonical El Niño, which is extensively studied for its dynamics and worldwide impacts. A typical El Niño event is marked by a warm anomaly of sea surface temperature (SST) in the equatorial eastern Pacific. Because of the associated changes in the surface winds and the weakening of coastal upwelling, the coasts of South America suffer from widespread fish mortality during the event. Quite opposite of this characteristic change in the ocean condition, cold SST anomalies prevail in the eastern equatorial Pacific during the El Niño Modoki events, but with the warm anomalies intensified in the central Pacific. The boreal winter condition of 2004 is a typical example of such an event, when a tripole pattern is noticed in the SST anomalies; warm central Pacific flanked by cold eastern and western regions. The SST anomalies are coupled to a double cell in anomalous Walker circulation with rising motion in the central parts and sinking motion on both sides of the basin. This is again a different feature compared to the well-known single-cell anomalous Walker circulation during El Niños. La Niña Modoki is the opposite phase of the El Niño Modoki, when a cold central Pacific is flanked by warm anomalies on both sides. The Modoki events are seen to peak in both boreal summer and winter and hence are not seasonally phase-locked to a single seasonal cycle like El Niño/La Niña events. Because of this distinction in the seasonality, the teleconnection arising from these events will vary between the seasons as teleconnection path will vary depending on the prevailing seasonal mean conditions in the atmosphere. Moreover, the Modoki El Niño/La Niña impacts over regions such as the western coast of the United States, the Far East including Japan, Australia, and southern Africa, etc., are opposite to those of the canonical El Niño/La Niña. For example, the western coasts of the United States suffer from severe droughts during El Niño Modoki, whereas those regions are quite wet during El Niño. The influences of Modoki events are also seen in tropical cyclogenesis, stratosphere warming of the Southern Hemisphere, ocean primary productivity, river discharges, sea level variations, etc. A remarkable feature associated with Modoki events is the decadal flattening of the equatorial thermocline and weakening of zonal thermal gradient. The associated ocean-atmosphere conditions have caused frequent and persistent developments of Modoki events in recent decades.

Article

Konrad Ott and Frederike Neuber

The means to combat dangerous anthropogenic climate change constitutes a portfolio. Beside abatement of greenhouse gas emissions, this portfolio entails adaptation to changing climate conditions, and so-called climate engineering measures. The overall portfolio has to be judged on technical, economic, and moral grounds. This requires an in-depth understanding of the moral aspects of climate engineering options. Climate engineering (CE) is a large-scale intentional intervention either in carbon cycles (carbon dioxide removal; CDR) or in solar radiation (solar radiation management; SRM). The ethical discourse on climate engineering has gained momentum since the 2010s. The set of arguments pro and contra specific CE technologies constitute a vast landscape of discourse. Single arguments must be analyzed with scrutiny according to their ethical background, their normative premises, their inferential logic, and their practical and political consequences. CE ethics, then, has a threefold task: (a) it must suppose a solid understanding of different CE technologies and their risks; (b) it has to analyze the moral arguments that speak in favor or against specific CE technologies; and (c) it has to assess the impacts of accepting or rejecting specific arguments for the overall climate portfolio’s design. The global climate portfolio differs from ordinary investment portfolios since stakes are huge, moral values in dispute, risks and uncertainties pervasive, and collective decision-making urgent. Any argument has implications of how to design the overall portfolio best. From an ethical perspective, however, one must reflect upon the premises and inferential structures of the arguments as such. Analysis of arguments and mapping them logically can be seen as core business of CE ethics. Highly general arguments about CE usually fall short, since the diverse features of individual technologies may not be addressed by overarching arguments that necessarily homogenize different technologies. It can be stated with confidence that the moral profiles of CDR and SRM are highly different. Every single deployment scheme ought to be judged specifically, for it is a huge difference to propose SRM as a substitute for abatement, or to embed it within a comprehensive climate portfolio including abatement and adaptation, where SRM will be used sporadically and only for a matter of decades.

Article

The growing concern about global warming has turned focus in Sweden and other Baltic countries toward the connection between history and climate. Important steps have been taken in the scientific reconstruction of climatic parables. Historic climate data have been published and analyzed, and various proxy data have been used to reconstruct historic climate curves. The results have revealed an ongoing regional warming from the late 17th to the early 21st century. The development was not continuous, however, but went on in a sequence of warmer and colder phases. Within the fields of history and socially oriented climate research, the industrial revolution has often been seen as a watershed between an older and a younger climate regime. The breakthrough of the industrial society was a major social change with the power to influence climate. Before this turning point, man and society were climate dependent. Weather and short-term climate fluctuations had major impacts on agrarian culture. When the crops failed several years in sequence, starvation and excess mortality followed. As late as 1867–1869, northern Sweden and Finland were struck by starvation due to massive crop failures. Although economic activities in the agricultural sector had climatic effects before the industrial society, when industrialization took off in Sweden in the 1880s it brought an end to the large-scale starvations, but also the start of an economic development that began to affect the atmosphere in a new and broader way. The industrial society, with its population growth and urbanization, created climate effects. Originally, however, the industrial outlets were not seen as problems. In the 18th century, it was thought that agricultural cultivation could improve the climate, and several decades after the industrial take-off there still was no environmental discourse in the Swedish debate. On the contrary, many leading debaters and politicians saw the tall chimneys, cars, and airplanes as hopeful signs in the sky. It was not until the late 1960s that the international environmental discourse reached Sweden. The modern climate debate started to make its imprints as late as the 1990s. During the last two decades, the Swedish temperature curve has unambiguously turned upwards. Thus, parallel to the international debate, the climate issue has entered the political agenda in Sweden and the other Nordic countries. The latest development has created a broad political consensus in favor of ambitious climate goals, and the people have gradually started to adapt their consumption and lifestyles to the new prerequisites.Although historic climate research in Sweden has had a remarkable expansion in the last decades, it still leans too much on its climate change leg. The clear connection between the climate fluctuations during the last 300 years and the major social changes that took place in these centuries needs to be further studied.

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.

Article

Carl Friedrich Gethmann and Georg Kamp

The expected climate change is and will be fraught with conflicts at private, societal, and global levels. Because of the temporal scope of the developments, future generations as well will be affected by its consequences. Therefore, the debate on how to cope with climate change and its consequences necessarily includes pivotal ethical questions. Philosophical ethics critically reviews suggestions and arguments given in the debate and develops justified solutions. It therefore analyzes conflict constellations, reconstructs the conditions of and options for their resolution, and defines the limits of justifiability. Even though individual behavior lies in the focus of ethical consideration, the specific conditions for acting make organized collective action indispensable for achieving relevant effects. Because nobody can be obligated to actions that he or she cannot perform at all, or at least not successfully, all on one’s own (ultra posse nemo obligatur), organized and institutionalized action lie in the focus of ethical consideration. States especially, with their organizational and regulative power, are indispensable to manage social conflicts, to overcome social dilemmas, and to create suitable conditions for effective measures. Because there is no privileged principle of justice that guides the distribution of burdens and benefits in international cooperation, the procedural fairness of international negotiation is of special significance.

Article

The signing of the United Nations Framework Convention on Climate Change (UNFCCC) by 154 nations at the Rio “Earth Summit” in 1992 marked the beginning of multilateral climate negotiations. Aiming for the “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system,” the Convention divided parties according to different commitments and established the common but differentiated responsibilities and respective capabilities (CBDRRC) principle. In 1997, parties to the Convention adopted the Kyoto Protocol, which entered into force in 2005. The Protocol set internationally binding emission reduction targets based on a rigid interpretation of the CBDRRC principle. Different perceptions on a fair distribution of climate change mitigation costs hindered multilateral efforts to tackle the problem. Climate change proved a “super wicked” challenge (intricately linked to security, development, trade, water, energy, food, land use, transportation, etc.) and this fact led to a lack of consensus on the distribution of rights and responsibilities among countries. Indeed, since 1992, greenhouse gas concentrations in the atmosphere have increased significantly and the Kyoto Protocol did not reverse the trend. In 2009, a new political framework, the Copenhagen Accord, was signed. Although parties recognized the need to limit global warming to < 2°C to prevent dangerous climate change, they did not agree on a clear path toward a legally-binding treaty to succeed the Kyoto Protocol, whose first commitment period would end in 2012. A consensus would only be reached in 2015, when a new, partially legally-binding treaty—the Paris Climate Agreement—committing all parties to limit global warming to “well below 2°C” was finally signed. It came into force in November 2016. Described in many political, public, and academic contexts as a diplomatic success, the agreement suffers, however, from several limitations to its effectiveness. The nationally determined contributions that parties have presented thus far under the agreement would limit warming to approximately 3°C by 2100, placing the Earth at a potentially catastrophic level of climate change. Forces that resist the profound transformations necessary to stabilize the Earth’s climate dominate climate change governance. Throughout almost three decades of international negotiations, global greenhouse gas (GHG) emissions have increased substantially and at a rapid pace, and climate change has worsened significantly.

Article

Pierre Camberlin

Eastern Africa, classically presented as a major dry climate anomaly region in the otherwise wet equatorial belt, is a transition zone between the monsoon domains of West Africa and the Indian Ocean. Its complex terrain, unequaled in the rest of Africa, results in a huge diversity of climatic conditions that steer a wide range of vegetation landscapes, biodiversity and human occupations. Meridional rainfall gradients dominate in the west along the Nile valley and its surroundings, where a single boreal summer peak is mostly observed. Bimodal regimes (generally peaking in April and November) prevail in the east, gradually shifting to a single austral summer peak to the south. The swift seasonal shift of the Intertropical Convergence Zone and its replacement in January–February and June–September by strong meridional, generally diverging low-level winds (e.g., the Somali Jet), account for the low rainfall. These large-scale flows interact with topography and lakes, which have their own local circulation in the form of mountain and lake breezes. This results in complex rainfall patterns, with a strong diurnal component, and a frequent asymmetry in the rainfall distribution with respect to the major relief features. Whereas highly organized rain-producing systems are uncommon, convection is partly modulated at intra-seasonal (about 30–60-day) timescales. Interannual variability shows a fair level of spatial coherence in the region, at least in July–September in the west (Ethiopia and Nile Valley) and October–December in the east along the Indian Ocean. This is associated with a strong forcing from sea-surface temperatures in the Pacific and Indian Oceans, and to a lesser extent the Atlantic Ocean. As a result, Eastern Africa shows some of the largest interannual rainfall variations in the world. Some decadal-scale variations are also found, including a drying trend of the March–May rainy season since the 1980s in the eastern part of the region. Eastern Africa overall mean temperature increased by 0.7 to 1 °C from 1973 to 2013, depending on the season. The strong, sometimes non-linear altitudinal gradients of temperature and moisture regimes, also contribute to the climate diversity of Eastern Africa.

Article

C.J.C. Reason

Southern Africa extends from the equator to about 34°S and is essentially a narrow, peninsular land mass bordered to its south, west, and east by oceans. Its termination in the mid-ocean subtropics has important consequences for regional climate, since it allows the strongest western boundary current in the world ocean (warm Agulhas Current) to be in close proximity to an intense eastern boundary upwelling current (cold Benguela Current). Unlike other western boundary currents, the Agulhas retroflects south of the land mass and flows back into the South Indian Ocean, thereby leading to a large area of anomalously warm water south of South Africa which may influence storm development over the southern part of the land mass. Two other unique regional ocean features imprint on the climate of southern Africa—the Angola-Benguela Frontal Zone (ABFZ) and the Seychelles-Chagos thermocline ridge (SCTR). The former is important for the development of Benguela Niños and flood events over southwestern Africa, while the SCTR influences Madden-Julian Oscillation and tropical cyclone activity in the western Indian Ocean. In addition to South Atlantic and South Indian Ocean influences, there are climatic implications of the neighboring Southern Ocean. Along with Benguela Niños, the southern African climate is strongly impacted by ENSO and to lesser extent by the Southern Annular Mode (SAM) and sea-surface temperature (SST) dipole events in the Indian and South Atlantic Oceans. The regional land–sea distribution leads to a highly variable climate on a range of scales that is still not well understood due to its complexity and its sensitivity to a number of different drivers. Strong and variable gradients in surface characteristics exist not only in the neighboring oceans but also in several aspects of the land mass, and these all influence the regional climate and its interactions with climate modes of variability. Much of the interior of southern Africa consists of a plateau 1 to 1.5 km high and a narrow coastal belt that is particularly mountainous in South Africa, leading to sharp topographic gradients. The topography is able to influence the track and development of many weather systems, leading to marked gradients in rainfall and vegetation across southern Africa. The presence of the large island of Madagascar, itself a region of strong topographic and rainfall gradients, has consequences for the climate of the mainland by reducing the impact of the moist trade winds on the Mozambique coast and the likelihood of tropical cyclone landfall there. It is also likely that at least some of the relativity aridity of the Limpopo region in northern South Africa/southern Zimbabwe results from the location of Madagascar in the southwestern Indian Ocean. While leading to challenges in understanding its climate variability and change, the complex geography of southern Africa offers a very useful test bed for improving the global models used in many institutions for climate prediction. Thus, research into the relative shortcomings of the models in the southern African region may lead not only to better understanding of southern African climate but also to enhanced capability to predict climate globally.

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

Ricardo García-Herrera and David Barriopedro

The Mediterranean is a semi-enclosed sea surrounded by Europe to the north, Asia to the east, and Africa to the south. It covers an area of approximately 2.5 million km2, between 30–46 °N latitude and 6 °W and 36 °E longitude. The term Mediterranean climate is applied beyond the Mediterranean region itself and has been used since the early 20th century to classify other regions of the world, such as California or South Africa, usually located in the 30º–40º latitudinal band. The Mediterranean climate can be broadly characterized by warm to hot dry summers and mild wet winters. However, this broad picture hides important variations, which can be explained through the existence of two geographical gradients: North/South, with a warmer and drier south, and West/East, more influenced by Atlantic/Asian circulation. The region is located at a crossroad between the mid-latitudes and the subtropical regimes. Thus, small changes in the Atlantic storm track may lead to dramatic changes in the precipitation of the northwestern area of the basin. The variability of the descending northern branch of the Hadley cell influences the climate of the southern margin, while the eastern border climate is conditioned by the Siberian High in winter and the Indian Summer Monsoon during summer. All these large-scale factors are modulated by the complex orography of the region, the contrasting albedo, and the moisture and heat supplied by the Mediterranean Sea. The interactions occurring among all these factors lead to a complex picture with some relevant phenomena characteristic of the Mediterranean region, such as heatwaves and droughts, Saharan dust intrusions, or specific types of cyclogenesis. Climate model projections generally agree in characterizing the region as a climate change hotspot, considering that it is one of the areas of the globe likely to suffer pronounced climate changes. Anthropogenic influences are not new, since the region is densely populated and is the home of some the oldest civilizations on Earth. This has produced multiple and continuous modifications in the land cover, with measurable impacts on climate that can be traced from the rich available documentary evidence and high-resolution natural proxies.

Article

Sharon E. Nicholson

This article provides an in-depth look at all aspects of the climate of the Sahel, including the pervasive dust in the Sahelian atmosphere. Emphasis is on two aspects: West African monsoon and the region’s rainfall regime. This includes an overview of the prevailing atmospheric circulation at the surface and aloft and the relationship between this and the rainfall regime. Aspects of the rainfall regime that are considered include its unique characteristics, its changes over time, the storm systems that produce rainfall, and factors governing its variability on interannual and decadal time scales. Variability is examined on three time scales: millennial (as seen is the paleo records of the last 20,000 years), multi-decadal (as seen over the last few centuries as seen from proxy data and, more recently, in observations), and interannual to decadal (quantified by observations from the late 19th century and onward). A unique feature of Sahel climate is that is rainfall regime is perhaps the most sensitive in the world and this sensitivity is apparent on all of these time scales.

Article

Western and Central Equatorial Africa (WCEA), home to the Congo rainforests, is the green heart of the otherwise dry continent of Africa. Despite its crucial role in the Earth system, WCEA’s climate variability has received little attention compared to the rest of Africa. Climate variability in the region is a result of complex interactions among various features acting on local and global scales. The mesoscale convective systems (MCSs) that have a preferentially westward propagation and present a distinct diurnal cycle are the main source of rainfall in the region. As a result of strong MCS activity, WCEA stands out as a convective anomaly within the tropics and experiences the world’s most intense thunderstorms as well as the highest lightning flash rates. The moisture of the region is supplied primarily from the Atlantic Ocean, with additional contributions from local recycling and East Africa. WCEA, in turn, serves as a moisture source for other parts of the continent. One striking characteristic of WCEA is its intrinsic heterogeneity with respect to interannual variability of rainfall, resulting in delineation of the region primarily in the zonal direction. This is in contrast to the meridionally oriented spatial variability of the annual cycle and underlines the fact that driving factors of the two can be quite different. The annual cycle is mainly determined by the seasonal excursion of the sun. However, the interannual and intraseasonal variability of the region are modulated by remote forcings from all three oceans, reflected via zonal atmospheric cells and equatorial wave dynamics. The local atmospheric jets and regional Walker-like circulations also contribute to WCEA’s climate variability by modulating the moisture transport and vertical motion. The region has experienced an increasing rate of deforestation in recent decades and has made a significant contribution to the global biomass burning emissions that can alter regional and global circulation, along with energy and water cycles. The mean annual temperature of the region has increased by about 1°C in the past 70 years. The annual rainfall over the same period presents a negative trend, though that is quite negligible in the eastern sector of the region.

Article

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. Africa, a continent with the largest number of countries falling under the category of Least Developed Countries (LDCs), remains highly dependent on rain-fed agriculture that suffers from low intake of water, exacerbating the vulnerability to climate variability and anthropogenic climate change. The increasing frequency and severity of climate extremes impose major strains on the economies of these countries. The loss of livelihoods due to interaction of climate change with existing stressors is elevating internal and cross-border migration. The continent is experiencing rapid urbanization, and its cities represent the most vulnerable locations to climate change due in part to incapacitated local governance. Overall, the institutional capacity to coordinate, regulate, and facilitate development in Africa is weak. The general public is less empowered to hold government accountable. The rule of law, media, and other watchdog organizations, and systems of checks and balances are constrained in different ways, contributing to poor governance and resulting in low capacity to respond to climate risks. As a result, climate policy and governance are inseparable in Africa, and capacitating the government is as essential as establishing climate policy. With the highest level of vulnerability to climate change compared with the rest of the world, governance in Africa is pivotal in crafting and implementing viable climate policies. It is indisputable that African climate policy should focus first and foremost on adaptation to climate change. It is pertinent, therefore, to assess Africa’s governance ability to identify and address the continent’s needs for adaptation. One key aspect of effective climate policy is access to up-to-date and contextually relevant information that encompasses indigenous knowledge. African countries have endeavored to meet international requirements for reports such as the National Communications on Climate Change Impacts and Vulnerabilities and the National Adaptation Programmes of Action (NAPAs). However, the capacity to deliver on-time quality reports is lacking; also the implementation, in particular integration of adaptation plans into the overall development agenda, remains a challenge. There are a few successes, but overall adaptation operates mainly at project level. Furthermore, the capacity to access and effectively utilize availed international resources, such as extra funding or technology transfer, is limited in Africa. While the continent is an insignificant source of emissions on a global scale, a more forward looking climate policy would require integrating adaptation with mitigation to put in place a foundation for transformation of the development agenda, towards a low carbon driven economy. Such a futuristic approach calls for a comprehensive and robust climate policy governance that goes beyond climate to embrace the Sustainable Development Goals Agenda 2030. Both governance and climate policy in Africa will need to be viewed broadly, encompassing the process of globalization, which has paved the way to a new geological epoch, the Anthropocene. The question is, what should be the focus of climate policy and governance across Africa under the Anthropocene era?

Article

The expansion and intensification of summer monsoon precipitation in North and East Africa during the African Humid Period (AHP; c. 15,000–5,000 years before present) is recorded by a wide range of natural archives, including lake and marine sediments, animal and plant remains, and human archaeological remnants. Collectively this diverse proxy evidence provides a detailed portrait of environmental changes during the AHP, illuminating the mechanisms, temporal and spatial evolution, and cultural impacts of this remarkable period of monsoon expansion across the vast expanse of North and East Africa. The AHP corresponds to a period of high local summer insolation due to orbital precession that peaked at ~11–10 ka, and it is the most recent of many such precessionally paced pluvial periods over the last several million years. Low-latitude sites in the North African tropics and Sahel record an intensification of summer monsoon precipitation at ~15 ka, associated with both rising summer insolation and an abrupt warming of the high northern latitudes at this time. Following a weakening of monsoon strength during the Younger Dryas cold period (12.9–11.7 ka), proxy data point to peak intensification of the West African monsoon between 10–8 ka. These data document lake and wetland expansions throughout almost all of North Africa, expansion of grasslands, shrubs and even some tropical trees throughout much of the Sahara, increases in Nile and Niger River runoff, and proliferation of human settlements across the modern Sahara. The AHP was also marked by a pronounced reduction in windblown mineral dust emissions from the Sahara. Proxy data suggest a time-transgressive end of the AHP, as sites in the northern and eastern Sahara become arid after 8–7 ka, while sites closer to the equator became arid later, between 5–3 ka. Locally abrupt drops in precipitation or monsoon strength appear to have been superimposed on this gradual, insolation-paced decline, with several sites to the north and east of the modern arid/semi-arid boundary showing evidence of century-scale shifts to drier conditions around 5 ka. This abrupt drying appears synchronous with rapid depopulation of the North African interior and an increase in settlement along the Nile River, suggesting a relationship between the end of the AHP and the establishment of proto-pharaonic culture. Proxy data from the AHP provide an important testing ground for model simulations of mid-Holocene climate. Comparisons with proxy-based precipitation estimates have long indicated that mid-Holocene simulations by general circulation models substantially underestimate the documented expansion of the West African monsoon during the AHP. Proxy data point to potential feedbacks that may have played key roles in amplifying monsoon expansion during the AHP, including changes in vegetation cover, lake surface area, and mineral dust loading. This article also highlights key areas for future research. Among these are the role of land surface and mineral aerosol changes in amplifying West African monsoon variability; the nature and drivers of monsoon variability during the AHP; the response of human populations to the end of the AHP; and understanding locally abrupt drying at the end of the AHP.

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Clustering techniques are used in the analysis of weather and climate to identify discrete groups of atmospheric and oceanic structures and evolutions that occur more frequently than would be expected based on a background distribution, such as a multivariate Gaussian distribution. Some of the techniques identify states that are also unusually long-lived (or persistent). Familiar examples of atmospheric states identified from cluster analysis include a small number of seasonal mean midlatitude response patterns to El Niño events, and on intra-seasonal timescales the North Atlantic Oscillation and the Pacific–North America patterns. On weather timescales, cluster analysis has been used to objectively identify a number of typical synoptic patterns familiar to forecasters. Cluster analysis has also been used to categorize cyclone tracks. A large variety of clustering techniques are available. One approach is to determine whether the underlying probability distribution contains multiple, distinct peaks, and to identify these peaks. The existence of more than one peak would indicate the existence of preferred states. These techniques rely on kernel density estimation and mixture modeling, and are most successful when applied to a very low-dimensional representation of the state space. The identification of multiple preferred states in higher dimensional representations can be achieved with the k-means and hierarchical clustering techniques. These techniques can be applied to cyclone tracks as well as to the usual meteorological variables. In certain applications it may be desirable to allow a given state to belong to multiple clusters with differing probabilities. The mixture modeling technique gives such probabilities, as does the fuzzy clustering generalization of the k-means approach. A technique that tries to objectively identify an ordered array of states (or patterns) that best fit the underlying distribution in some sense makes use of self-organizing maps. An alternative approach that identifies not only preferred states but also ones that are unusually persistent is the Hidden Markov method. The Hidden Markov method makes use of an underlying “hidden variable” whose evolution is modeled by a Markov process. This method can be generalized further to detect long-term changes in the population of the clusters by letting the evolution of the hidden state be governed by a non-stationary finite element vector autoregressive factor process.

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In recent years, scientists have identified cognitive processes that short-circuit our deliberative faculties. In the domain of climate change in particular, a number of psychological barriers and biases may disrupt typical discourse and reflection and may even prevent those who are aware of climate change from taking action to mitigate or reduce its impact. These processes include the use of heuristic versions of calculation-based decisions to reduce processing load, which can make climate change judgments responsive to situational factors in the immediate decision context. Recent research in the decision sciences provides insight into how common biases in judgment inhibit rational deliberation about climate change, which may lead to the gap between society’s recognition of environmental problems and society’s frequent failure to address them appropriately. These insights involve the finite nature of human attention and cognitive resources, the complex interactions of personal experience and emotion, the challenges that uncertainty and risk place on behavior, and the profoundly social nature of human action. Understanding these barriers and systematic biases have led to a set of potential interventions, which demonstrate how practitioners can put research insights into practice in order to address a variety of sustainability challenges. One important direction for these interventions involves changing the decision context in ways that account for decision bias (e.g., using green defaults) and triggering more adaptive decisions as a result.

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The term public engagement (PE) refers to processes that provide a distinct role for citizens or stakeholder groups in policymaking. Such engagement is distinctive because it aims to create opportunities for mutual learning among policymakers, scientists, stakeholders, and members of the public. In so doing, PE involves a particular type of voice in public debate and policymaking that is different from more established discourses, such as those expressed through official policymaking channels, scientific institutions, civil society activists, or the public media. By the early 1970s, PE had emerged in the context of an overall democratization movement in Western societies through such innovations as the “citizen jury” in the United States and “planning cells” in Germany. Today, it is often more pragmatically motivated, such as in the European Commission, where PE is seen as a tool for responsible research and innovation that helps to anticipate and assess potential implications and societal expectations of research and innovation, as well as to design more inclusive and sustainable research policies. The first global PE processes in history were created to incorporate citizen voices into United Nations (UN) conventions on biodiversity and climate change. Building on theories of deliberative democracy and tested PE practices, a new World Wide Views process was developed to provide informed and considered input from ordinary citizens to the 2009 UN climate summit. This and subsequent World Wide Views (WWViews) deliberations have demonstrated that PE may potentially open up policy discourses that are constricted and obfuscated by organized interests. A telling example is provided by the World Wide Views on Climate and Energy deliberation held on June 5, 2015, where nearly 10,000 ordinary citizens gathered in 76 countries to consider and express their views on the issues to be addressed at the UN climate summit in Paris later that year. In a noteworthy departure from prevailing media and policy discourses, two-thirds of the participating citizens saw measures to fight climate change as “mostly an opportunity to improve our quality of life,” while only a quarter saw them as “mostly a threat to our quality of life,” a result that was consistent across high-, middle-, and low-income countries. Recent research on PE has indicated that when effectively implemented, such processes can increase the legitimacy, quality, and capacity of decision-making. Earlier aspirations for broader impacts, such as the democratization of policymaking at all levels, are now less prominent but arguably indispensable for achieving both immediate and longer-range goals. The relatively new concept of a deliberative system captures this complexity by moving beyond the narrow focus on single PE events encountered in much research to date, recognizing that single events rarely affect the course of policymaking. The evolving prospects for PE in biodiversity and climate change policy, therefore, can be seen as requiring ongoing improvements in the capacities of the deliberative system.