Arid environments cover about one third of the Earth’s surface, comprising the most extensive of the terrestrial biomes. Deserts show considerable individual variation in climate, geomorphic surface expression, and biogeography. Climatically, deserts range from dry interior environments, with large temperature ranges, to humid and relatively cool coastal environments, with small temperature ranges. What all deserts share in common is a consistent deficit of precipitation relative to water loss by evaporation, implying that the biological availability of water is very low. Deserts develop because of climatic (persistent high-pressure cells), topographic (mountain ranges that cause rain shadow effects), and oceanographic (cold currents) factors that limit the amount of rain or snowfall that a region receives. Most global deserts are subtropical in distribution.
There is a large range of geomorphic surfaces, including sand sheets and sand seas (ergs), stone pavements, bedrock outcrops, dry lakebeds, and alluvial fans. Vegetation cover is generally sparse, but may be enhanced in areas of groundwater seepage or along river courses. The limited vegetation cover affects fluvial and slope processes and results in an enhanced role for the wind. While the majority of streams in deserts are ephemeral features, both intermittent and perennial rivers develop in response to snowmelt in nearby mountains or runoff from distant, more well-watered regions. Most drainage is endoreic, meaning that it flows internally into closed basins and does not reach the sea, being disposed of by seepage and evaporation.
The early study of deserts was largely descriptive. More process-based studies commenced with the study of North American deserts in the mid- to late-1800s. Since the late 20th century, research has expanded into many areas of the world, with notable contributions coming from China, but our knowledge of deserts is still more compete in regions such as North America, Australia, Israel, and southern Africa, where access and funding have been more consistently secure. The widespread availability of high-quality remotely sensed images has contributed to the spread of study into new global field areas. The temporal framework for research has also improved, benefiting from improvements in geochronological techniques. Geochronological controls are vital to desert research because most arid regions have experienced significant climatic changes. Deserts have not only expanded or contracted in size, but have experienced changes in the dominant geomorphic processes and biogeographic environment. Contemporary scientific work has also benefited from improvements in technology, notably in surveying techniques, and from the use of quantitative modeling.
Boreal countries are rich in forest resources, and for their area, they produce a disproportionally large share of the lumber, pulp, and paper bound for the global market. These countries have long-standing strong traditions in forestry education and institutions, as well as in timber-oriented forest management. However, global change, together with evolving societal values and demands, are challenging traditional forest management approaches. In particular, plantation-type management, where wood is harvested with short cutting cycles relative to the natural time span of stand development, has been criticized. Such management practices create landscapes composed of mosaics of young, even-aged, and structurally homogeneous stands, with scarcity of old trees and deadwood. In contrast, natural forest landscapes are characterized by the presence of old large trees, uneven-aged stand structures, abundant deadwood, and high overall structural diversity. The differences between managed and unmanaged forests result from the fundamental differences in the disturbance regimes of managed versus unmanaged forests. Declines in managed forest biodiversity and structural complexity, combined with rapidly changing climatic conditions, pose a risk to forest health, and hence, to the long-term maintenance of biodiversity and provisioning of important ecosystem goods and services. The application of ecosystem management in boreal forestry calls for a transition from plantation-type forestry toward more diversified management inspired by natural forest structure and dynamics.
Enuvie G. Akpokodje
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.
Deltas have played a significant role in the growth of human civilization because of their economic and ecological importance, and their recurring water related hazards. They are endowed with abundant natural resources (oil, gas, water, etc.), highly productive agricultural land, rich biodiversity, extensive wetland ecosystems, and waterways. Deltas cover about 1% of the earth’s surface, with an estimated total human population of over 500 million and an average density of about 500/km2. The combined population of the Ganges-Brahmaputra, Yangtze, and Nile deltas in 2000 was 230 million, which was expected to increase by 35% in 2015. Some of the world’s large urban cities (Shanghai, Bangkok, Dhaka, Cairo, New Orleans, etc.) are located in deltas.
Globally, urban deltas and associated coastal regions are becoming increasingly vulnerable because of the impact of intensive human development, high population growth, climate change, and sea level rise. In addition, a significant number of the world's major deltas are experiencing subsidence and severe flooding. The trapping of sediments behind dams constructed upstream from deltas constitutes another major threat to the long-term stability of deltas.
The future of the environment of planet earth has been a subject of extensive research because of the growing threat to the sustainability of the earth’s environment. In 2013, the International Association of Hydrological Sciences (IAHS) launched the “Future Earth” decadal research initiative, aimed at bringing together the environmental and social sciences to promote sustainable development. A 10-year “Global Delta Sustainability” initiative was declared the same year because deltas constitute important sub-sets of “Future Earth.” The goal of the Global Delta Sustainability initiative is to focus attention on the value and vulnerabilities of deltas worldwide, and to promote international and regional cooperation among scientists, policymakers, and other stakeholders.
Geology has always played an important role in the development of human society. Recently, Environmental Geology has emerged as a sub-discipline with a strong interdisciplinary approach (integrating other science disciplines, economics, law, etc.) to the understanding of geologic processes and the application of geological science to issues directly related to human activities. Environmental geology focuses attention on human interactions with earth processes, resources, and environment, and it identifies constraints imposed on human activities by geologic processes and vice versa. The key environmental geologic challenges, especially in urban delta areas are: increasing exposure of large human populations and infrastructures to geologic hazards (flooding, cyclones, etc.), provision of adequate and quality drinking water, safe waste disposal, contamination of soil, and water resources.
The restoration and maintenance of the sustainability of deltas require the development of integrated management strategies that incorporate extensive research, monitoring, and intensive consultation with the people whose activities are affecting and/or affected by deltas. The strongly interdisciplinary approach of Environmental Geology and its rapidly growing importance hold greater prospects for a better understanding of deltas as vulnerable, complex, socio-ecologic systems and ensures better preparedness in protecting, restoring, and mitigating them in a rapidly changing global environment.
There is scientific consensus that human activities have been altering the atmospheric composition and are a key driver of global climate and environmental changes since pre-industrial times (IPCC, 2013). It is a pressing priority to understand the Earth system response to atmospheric aerosol input from diverse sources, which so far remain one of the largest uncertainties in climate studies (Boucher et al., 2014; Forster et al., 2007). As the second most abundant component (in terms of mass) of atmospheric aerosols, mineral dust exerts tremendous impacts on Earth’s climate and environment through various interaction and feedback processes. Dust can also have beneficial effects where it deposits: Central and South American rain forests get most of their mineral nutrients from the Sahara; iron-poor ocean regions get iron; and dust in Hawaii increases plantain growth. In northern China as well as the midwestern United States, ancient dust storm deposits known as loess are highly fertile soils, but they are also a significant source of contemporary dust storms when soil-securing vegetation is disturbed. Accurate assessments of dust emission are of great importance to improvements in quantifying the diverse dust impacts.
Lora Fleming, Michael Depledge, Niall McDonough, Mathew White, Sabine Pahl, Melanie Austen, Anders Goksoyr, Helena Solo-Gabriele, and John Stegeman
The interdisciplinary study of oceans and human health is an area of increasing global importance. There is a growing body of evidence that the health of the oceans and that of humans are inextricably linked and that how we interact with and affect our oceans and seas will significantly influence our future on earth. Since the emergence of modern humans, the oceans have served as a source of culture, livelihood, expansion, trade, food, and other resources. However, the rapidly rising global population and the continuing alterations of the coastal environment are placing greater pressure on coastal seas and oceans. Negative human impacts, including pollution (chemical, microbial, material), habitat destruction (e.g., bottom trawling, dredging), and overfishing, affect not only ecosystem health, but also human health. Conversely, there is potential to promote human health and well-being through sustainable interactions with the coasts and oceans, such as the restoration and preservation of coastal and marine ecosystems.
The study of oceans and human health is inherently interdisciplinary, bringing together the natural and social sciences as well as diverse stakeholder communities (including fishers, recreational users, private enterprise, and policymakers). Reviewing history and policy with regard to oceans and human health, in addition to known and potential risks and benefits, provides insights into new areas and avenues of global cooperation, with the possibility for collaboratively addressing the local and global challenges of our interactions with the oceans, both now and in the future.