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Some of the most significant impacts of climate change are likely to be felt in water resources management, but climate change is not the only uncertainty facing water managers and policymakers. The concept of water security has emerged to address social, economic, political, and environmental factors, as well as the physical determinants of water availability. There are significant challenges for communicating about water security under a changing climate. Water security shares many of the characteristics of climate change with regards to communication. It is a complex concept involving interactions between dynamic human and natural systems, requiring public deliberation and engagement to inform political debate and to facilitate behavioral and cultural change. Knowledge and values about water and climate change are communicated through material experiences as well as through language. Communication about water security and climate change takes many forms, which can be characterized as five key modes—policy, communication campaigns, media, cultures, and environments. More effective communication about climate change and water is needed across these different modes to support meaningful participation and deliberation in policy decisions by a wide range of stakeholders. Integrating climate change into communication campaigns about water security provides opportunities to challenge and reframe traditional formulations of the role of water in society and culture and how to manage water in human settlements, the economy, and the environment. The central challenge for communicating the impacts of climate change on water scarcity lies in the complex interactions between society, policy, technology, infrastructure, the economy, and the environment in modern water systems. Different modes of communication are useful to enable public and stakeholder engagement in understanding the issues and making decisions about how to ensure water security in a changing society and environment.

Article

Post-glacial aquatic ecosystems in Eurasia and North America, such as the Baltic Sea, evolved in the freshwater, brackish, and marine environments that fringed the melting glaciers. Warming of the climate initiated sea level and land rise and subsequent changes in aquatic ecosystems. Seminal ideas on ancient developing ecosystems were based on findings in Swedish large lakes of species that had arrived there from adjacent glacial freshwater or marine environments and established populations which have survived up to the present day. An ecosystem of the first freshwater stage, the Baltic Ice Lake initially consisted of ice-associated biota. Subsequent aquatic environments, the Yoldia Sea, the Ancylus Lake, the Litorina Sea, and the Mya Sea, are all named after mollusc trace fossils. These often convey information on the geologic period in question and indicate some physical and chemical characteristics of their environment. The ecosystems of various Baltic Sea stages are regulated primarily by temperature and freshwater runoff (which affects directly and indirectly both salinity and nutrient concentrations). Key ecological environmental factors, such as temperature, salinity, and nutrient levels, not only change seasonally but are also subject to long-term changes (due to astronomical factors) and shorter disturbances, for example, a warm period that essentially formed the Yoldia Sea, and more recently the “Little Ice Age” (which terminated the Viking settlement in Iceland). There is no direct way to study the post-Holocene Baltic Sea stages, but findings in geological samples of ecological keystone species (which may form a physical environment for other species to dwell in and/or largely determine the function of an ecosystem) can indicate ancient large-scale ecosystem features and changes. Such changes have included, for example, development of an initially turbid glacial meltwater to clearer water with increasing primary production (enhanced also by warmer temperatures), eventually leading to self-shading and other consequences of anthropogenic eutrophication (nutrient-rich conditions). Furthermore, the development in the last century from oligotrophic (nutrient-poor) to eutrophic conditions also included shifts between the grazing chain (which include large predators, e.g., piscivorous fish, mammals, and birds at the top of the food chain) and the microbial loop (filtering top predators such as jellyfish). Another large-scale change has been a succession from low (freshwater glacier lake) biodiversity to increased (brackish and marine) biodiversity. The present-day Baltic Sea ecosystem is a direct descendant of the more marine Litorina Sea, which marks the beginning of the transition from a primeval ecosystem to one regulated by humans. The recent Baltic Sea is characterized by high concentrations of pollutants and nutrients, a shift from perennial to annual macrophytes (and more rapid nutrient cycling), and an increasing rate of invasion by non-native species. Thus, an increasing pace of anthropogenic ecological change has been a prominent trend in the Baltic Sea ecosystem since the Ancylus Lake. Future development is in the first place dependent on regional factors, such as salinity, which is regulated by sea and land level changes and the climate, and runoff, which controls both salinity and the leaching of nutrients to the sea. However, uncertainties abound, for example the future development of the Gulf Stream and its associated westerly winds, which support the sub-boreal ecosystems, both terrestrial and aquatic, in the Baltic Sea area. Thus, extensive sophisticated, cross-disciplinary modeling is needed to foresee whether the Baltic Sea will develop toward a freshwater or marine ecosystem, set in a sub-boreal, boreal, or arctic climate.

Article

The Baltic Sea catchment area extends from the upper course of the Elbe in the Czech Republic to northernmost Lapland where the Tornionjoki river (Sw. Torneälven = Lake Torne) marks the border between Finland and Sweden today. This article concentrates on the coastal regions of the sea and discusses a mutual dialogue between climate and man. Oxygen isotope 18O and hydrogen isotope 2H in the layers of polar ice sheets indicate climate change in the time span of thousands, even tens of thousands, of years. In northern areas, much climatologic information is based on polar ice drilling data from Greenland. The influence of climate changes on human subsistence is clearly visible in pollen data from the numerous ponds and swamps in the Baltic Sea coastal zone. Accelerator mass spectrometry (AMS) dating of carbon remains in archaeological materials (such as the crusts of ceramic pieces) are used to build detailed chronological sequences. Human adaption to conditions dictated by nature is usually interpreted as innovation and progress in prehistory. But numerous raw materials, once used, cannot be replaced, while land exploitation is often followed by side effects such as erosion and eutrophication. For example, the Neolithic “revolution”—the beginning of crop cultivation and large-scale cattle breeding—is an example of such changes in southern Europe from ca. 6,000 bce. Between ca. 200 bce and 100 ce, during the Early Iron Age, the climate was relatively warm here. Local iron production expanded in the Baltic Sea region and allowed effective slash-and-burn crop cultivation for the first time in prehistory. Since then, human activity has caused damage to forests all around the Baltic Sea. A colder phase followed in 100–600 ce. Even today slight changes in annual temperature have great impact on subsistence in areas with harsh climate conditions, such as close to the Polar Circle. An abrupt and radical fall of temperature surely caused severe difficulties. Hunter-gatherers had to find secondary food resources while societies which were strongly dependent on one single base for economy, like agriculture, had even greater difficulties. In the southern part of the Baltic Sea sphere, considerable areas of land were under cultivation at that time. Harvest failures led to famines. A climate catastrophe, probably caused by volcanic eruption, adversely impacted urban, peasant, nomadic, and hunting populations all over the northern hemisphere in 535–536 ce. Recent archaeological studies and AMS samples have proven there was a demographic crisis in the northern part of the Baltic Sea. Soon after 600 ce, the climate became milder again, and the following centuries were warmer than almost any period during Holocene: the warm phase from 800 to ca.1050 ce perfectly matches a historical and archaeological era: the Viking Period. The Middle Ages and early post-medieval period were relatively mild and human-friendly times. But this was followed by the so-called Little Ice Age, dated approximately to 1275–1870. With the beginning of industrialization in mid-19th century, human impact on climate became obvious all over the globe, and the Baltic Sea region is no exception.

Article

A. Johannes Dolman, Luis U. Vilasa-Abad, and Thomas A. J. Janssen

Drylands cover around 40% of the land surface on Earth and are inhabited by more than 2 billion people, who are directly dependent on these lands. Drylands are characterized by a highly variable rainfall regime and inherent vegetation-climate feedbacks that can enhance the resilience of the system, but also can amplify disturbances. In that way, the system may get locked into two alternate stable states: one relatively wet and vegetated, and the other dry and barren. The resilience of dryland ecosystems derives from a number of adaptive mechanisms by which the vegetation copes with prolonged water stress, such as hydraulic redistribution. The stochastic nature of both the vegetation dynamics and the rainfall regime is a key characteristic of these systems and affects its management in relation to the feedbacks. How the ecohydrology of the African drylands will change in the future depends on further changes in climate, human disturbances, land use, and the socioeconomic system.

Article

The Tibetan Plateau (TP) is subjected to strong interactions among the atmosphere, hydrosphere, cryosphere, and biosphere. The Plateau exerts huge thermal forcing on the mid-troposphere over the mid-latitude of the Northern Hemisphere during spring and summer. This region also contains the headwaters of major rivers in Asia and provides a large portion of the water resources used for economic activities in adjacent regions. Since the beginning of the 1980s, the TP has undergone evident climate changes, with overall surface air warming and moistening, solar dimming, and decrease in wind speed. Surface warming, which depends on elevation and its horizontal pattern (warming in most of the TP but cooling in the westernmost TP), was consistent with glacial changes. Accompanying the warming was air moistening, with a sudden increase in precipitable water in 1998. Both triggered more deep clouds, which resulted in solar dimming. Surface wind speed declined from the 1970s and started to recover in 2002, as a result of atmospheric circulation adjustment caused by the differential surface warming between Asian high latitudes and low latitudes. The climate changes over the TP have changed energy and water cycles and has thus reshaped the local environment. Thermal forcing over the TP has weakened. The warming and decrease in wind speed lowered the Bowen ratio and has led to less surface sensible heating. Atmospheric radiative cooling has been enhanced, mainly through outgoing longwave emission from the warming planetary system and slightly enhanced solar radiation reflection. The trend in both energy terms has contributed to the weakening of thermal forcing over the Plateau. The water cycle has been significantly altered by the climate changes. The monsoon-impacted region (i.e., the southern and eastern regions of the TP) has received less precipitation, more evaporation, less soil moisture and less runoff, which has resulted in the general shrinkage of lakes and pools in this region, although glacier melt has increased. The region dominated by westerlies (i.e., central, northern and western regions of the TP) received more precipitation, more evaporation, more soil moisture and more runoff, which together with more glacier melt resulted in the general expansion of lakes in this region. The overall wetting in the TP is due to both the warmer and moister conditions at the surface, which increased convective available potential energy and may eventually depend on decadal variability of atmospheric circulations such as Atlantic Multi-decadal Oscillation and an intensified Siberian High. The drying process in the southern region is perhaps related to the expansion of Hadley circulation. All these processes have not been well understood.

Article

Biomass burning is widespread in sub-Saharan Africa, which harbors more than half of global biomass burning activity. These African open fires are mostly induced by humans for various purposes, ranging from agricultural land clearing and residue burning to deforestation. They affect a wide variety of land ecosystems, including forests, woodlands, shrublands, savannas, grasslands, and croplands. Satellite observations show that fires are distributed almost equally between the northern and southern hemispheres of sub-Saharan Africa, with a dipole-type annual distribution pattern, peaking during the dry (winter) season of either hemisphere. The widespread nature of African biomass burning and the tremendous amounts of particulate and gas-phase emissions the fires produce have been shown to affect a variety of processes that ultimately impact the earth’s atmospheric composition and chemistry, air quality, water cycle, and climate in a significant manner. However, there is still a high level of uncertainty in the quantitative characterization of biomass burning, and its emissions and impacts in Africa and globally. These uncertainties can be potentially alleviated through improvements in the spatial and temporal resolutions of satellite observations, numerical modeling and data assimilation, complemented by occasional field campaigns. In addition, there is great need for the general public, policy makers, and funding organizations within Africa to recognize the seriousness of uncontrolled biomass burning and its potential consequences, in order to bring the necessary human and financial resources to bear on essential policies and scientific research activities that can effectively address the threats posed by the combined adverse influences of the changing climate, biomass burning, and other environmental challenges in sub-Saharan Africa.

Article

Nathalie de Noblet-Ducoudré and Andrew J. Pitman

The land surface is where humans live and where they source their water and food. The land surface plays an important role in climate and anthropogenic climate change both as a driver of change and as a system that responds to change. Soils and vegetation influence the exchanges of water, energy and carbon between the land and the overlying atmosphere and thus contribute to the variability and the evolution of climate. But the role of the land in climate is scale dependent which means different processes matter on different timescales and over different spatial scales. Climate change alters the functioning of the land with changes in the seasonal cycle of ecosystem growth, in the extent of forests, the melt of permafrost, the magnitude and frequency of disturbances such as fire, drought, … Those changes feedback into climate at both the global and the regional scales. In addition, humans perturb the land conditions via deforestation, irrigation, urbanization, … and this directly affects climatic conditions at the local to regional scales with also sometimes global consequences via the release of greenhouse gases. Not accounting for land surface processes in climate modelling, whatever the spatial scale, will result in biases in the climate simulations.

Article

Elevation-dependent climate change has been observed in the European Alps in the context of global warming and as a consequence of Alpine orography. It is most obvious in elevation-dependent warming, conveniently defined as the linear regression of the time series of temperatures against elevation, and it reaches values of several tenths of a degree per 1,000 m elevation per decade. Observed changes in temperature have forced changes in atmospheric pressure, water vapor, cloud condensation, fluxes of infrared and solar radiation, snow cover, and evaporation, which have affected the Alpine surface energy and water balance in different ways at different elevations. At the same time, changes in atmospheric aerosol optical depth, in atmospheric circulation, and in the frequency of weather types have contributed to the observed elevation-dependent climate change in the European Alps. To a large extent, these observations have been reproduced by model simulations.