ABCs consist of anthropogenic aerosols such as sulfates, nitrates, organics, and black carbon and natural dust aerosols. The brownish color of the cloud which is visible when looking at the horizon is due to absorption of solar radiation at short wavelengths green, blue, and UV by organic and black carbon aerosols as well as by NOx.
While the local nature of ABCs around polluted cities has been known since the early s, the widespread transoceanic and transcontinental nature of ABCs as well as their large-scale effects on climate, hydrological cycle, and agriculture were discovered inadvertently by The Indian Ocean Experiment INDOEX , an international experiment conducted in the s over the Indian Ocean. The dimming was shown to be accompanied by significant atmospheric absorption of solar radiation by black and brown carbon a form of organic carbon.
The dimming by sulfates, nitrates, and carbonaceous black and organic carbon species has been shown to disrupt and weaken the monsoon circulation over southern Asia. Most significantly, the aerosols in ABCs near the ground lead to about 4 million premature mortalities every year. Technological and regulatory measures are available to mitigate most of the pollution resulting from ABCs.
This ABC program subsequently led to the identification of short-lived climate pollutants as potent mitigation agents of climate change, and in recognition, UNEP formed the Climate and Clean Air Coalition to deal with these pollutants. Biodiversity Generation and Loss. Human activities in the Anthropocene are influencing the twin processes of biodiversity generation and loss in complex ways that threaten the maintenance of biodiversity levels that underpin human well-being.
Yet many scientists and practitioners still present a simplistic view of biodiversity as a static stock rather than one determined by a dynamic interplay of feedback processes that are affected by anthropogenic drivers. Biodiversity describes the variety of life on Earth, from the genes within an organism to the ecosystem level. However, this article focuses on variation among living organisms, both within and between species.
Within species, biodiversity is reflected in genetic, and consequent phenotypic, variations among individuals. Genetic diversity is generated by germ line mutations, genetic recombination during sexual reproduction, and immigration of new genotypes into populations. Across species, biodiversity is reflected in the number of different species present and also, by some metrics, in the evenness of their relative abundance.
At this level, biodiversity is generated by processes of speciation and immigration of new species into an area. Anthropogenic drivers affect all these biodiversity generation processes, while the levels of genetic diversity can feed back and affect the level of species diversity, and vice versa. Therefore, biodiversity maintenance is a complex balance of processes and the biodiversity levels at any point in time may not be at equilibrium.
A major concern for humans is that our activities are driving rapid losses of biodiversity, which outweigh by orders of magnitude the processes of biodiversity generation. A wide range of species and genetic diversity could be necessary for the provision of ecosystem functions and services e. The importance of biodiversity becomes particularly marked over longer time periods, and especially under varying environmental conditions.
In terms of biodiversity losses, there are natural processes that cause roughly continuous, low-level losses, but there is also strong evidence from fossil records for transient events in which exceptionally large loss of biodiversity has occurred. These major extinction episodes are thought to have been caused by various large-scale environmental perturbations, such as volcanic eruptions, sea-level falls, climatic changes, and asteroid impacts.
From all these events, biodiversity has shown recovery over subsequent calmer periods, although the composition of higher-level evolutionary taxa can be significantly altered. In the modern era, biodiversity appears to be undergoing another mass extinction event, driven by large-scale human impacts. The primary mechanisms of biodiversity loss caused by humans vary over time and by geographic region, but they include overexploitation, habitat loss, climate change, pollution e.
It is worth noting that human activities may also lead to increases in biodiversity in some areas through species introductions and climatic changes, although these overall increases in species richness may come at the cost of loss of native species, and with uncertain effects on ecosystem service delivery. Genetic diversity is also affected by human activities, with many examples of erosion of diversity through crop and livestock breeding or through the decline in abundance of wild species populations.
Significant future challenges are to develop better ways to monitor the drivers of biodiversity loss and biodiversity levels themselves, making use of new technologies, and improving coverage across geographic regions and taxonomic scope.
Biodiversity Hotspots and Conservation Priorities. The concept of biodiversity hotspots arose as a science-based framework with which to identify high-priority areas for habitat protection and conservation—often in the form of nature reserves. The basic idea is that with limited funds and competition from humans for land, we should use range maps and distributional data to protect areas that harbor the greatest biodiversity and that have experienced the greatest habitat loss.
In its early application, much analysis and scientific debate went into asking the following questions: Should all species be treated equally? Do endemic species matter more? Should the magnitude of threat matter? Does evolutionary uniqueness matter? And if one has good data on one broad group of organisms e. Early applications also recognized that hotspots could be identified at a variety of spatial scales—from global to continental, to national to regional, to even local.
Hence, within each scale, it is possible to identify biodiversity hotspots as targets for conservation. In the last 10 years, the concept of hotspots has been enriched to address some key critiques, including the problem of ignoring important areas that might have low biodiversity but that certainly were highly valued because of charismatic wild species or critical ecosystem services.
Analyses revealed that although the spatial correlation between high-diversity areas and high-ecosystem-service areas is low, it is possible to use quantitative algorithms that achieve both high protection for biodiversity and high protection for ecosystem services without increasing the required area as much as might be expected. Currently, a great deal of research is aimed at asking about what the impact of climate change on biodiversity hotspots is, as well as to what extent conservation can maintain high biodiversity in the face of climate change.
Finally, conservation planning has most recently embraced what is in some sense the inverse of biodiversity hotspots—what we might call conservation wastelands. This approach recognizes that in the Anthropocene epoch, human development and infrastructure are so vast that in addition to using data to identify biodiversity hotspots, we should use data to identify highly degraded habitats and ecosystems.
These degraded lands can then become priority development areas—for wind farms, solar energy facilities, oil palm plantations, and so forth. By specifying degraded lands, conservation plans commonly pair maps of biodiversity hotspots with maps of degraded lands that highlight areas for development. By putting the two maps together, it should be possible to achieve much more effective conservation because there will be provision of habitat for species and for economic development—something that can obtain broader political support than simply highlighting biodiversity hotspots.
Causes of Soil Salinization, Sodification, and Alkalinization. Driving forces for natural soil salinity and alkalinity are climate, rock weathering, ion exchange, and mineral equilibria reactions that ultimately control the chemical composition of soil and water.
The major weathering reactions that produce soluble ions are tabled. Where evapotranspiration is greater than precipitation, downward water movement is insufficient to leach solutes out of the soil profile and salts can precipitate. Microbes involved in organic matter mineralization and thus the carbon, nitrogen, and sulfur biogeochemical cycles are also implicated. Seasonal contrast and evaporative concentration during dry periods accelerate short-term oxidation-reduction reactions and local and regional accumulation of carbonate and sulfur minerals.
The presence of salts and alkaline conditions, together with the occurrence of drought and seasonal waterlogging, creates some of the most extreme soil environments where only specially adapted organisms are able to survive. Sodic soils are alkaline, rich in sodium carbonates, with an exchange complex dominated by sodium ions. Such sodic soils, when low in other salts, exhibit dispersive behavior, and they are difficult to manage for cropping.
Maintaining the productivity of sodic soils requires control of the flocculation-dispersion behavior of the soil. Poor land management can also lead to anthropogenically induced secondary salinity. New developments in physical chemistry are providing insights into ion exchange and how it controls flocculation-dispersion in soil.
Classification and Mitigation of Soil Salinization. Soil salinity has been causing problems for agriculturists for millennia, primarily in irrigated lands. The importance of salinity issues is increasing, since large areas are affected by irrigation-induced salt accumulation. A wide knowledge base has been collected to better understand the major processes of salt accumulation and choose the right method of mitigation.
There are two major types of soil salinity that are distinguished because of different properties and mitigation requirements. The first is caused mostly by the large salt concentration and is called saline soil, typically corresponding to Solonchak soils.
The second is caused mainly by the dominance of sodium in the soil solution or on the soil exchange complex. Saline soils have homogeneous soil profiles with relatively good soil structure, and their appropriate mitigation measure is leaching.
Naturally sodic soils have markedly different horizons and unfavorable physical properties, such as low permeability, swelling, plasticity when wet, and hardness when dry, and their limitation for agriculture is mitigated typically by applying gypsum. Salinity and sodicity need to be chemically quantified before deciding on the proper management strategy.
The most complex management and mitigation of salinized irrigated lands involves modern engineering including calculations of irrigation water rates and reclamation materials, provisions for drainage, and drainage disposal. Mapping-oriented soil classification was developed for naturally saline and sodic soils and inherited the first soil categories introduced more than a century ago, such as Solonchak and Solonetz in most of the total of 24 soil classification systems used currently.
Climate Change Impacts on Agriculture across Africa. Confidence in the projected impacts of climate change on agricultural systems has increased substantially since the first Intergovernmental Panel on Climate Change IPCC reports. 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.
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. 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.
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.
Carbon has been part of the Earth since its beginning, and the carbon cycle is well understood. However, its abundance in the atmosphere has become a problem. Those who propose solutions in decentralized market economies often prefer economic incentives to direct government regulation. Carbon cap-and-trade programs and carbon tax programs are the prime candidates to reign in emissions by altering the economic conditions under which producers and consumers make decisions.
This distortion is caused by overproduction and underpricing of carbon-related goods and services. The ideal level of emissions would be set under cap-and-trade, or be the outcome of an ideally set carbon tax. The ideal price of carbon permits would result from demand generated by government decree meeting an ideal fixed supply set by the government. The economic benefit of using the ideal carbon tax or the ideal permit price occurs because heterogeneous decision-makers will conceptually reduce emissions to the level that equates their marginal incremental emissions-reduction cost to the tax or permit price.
When applying the theory to the real world, ideal conditions with full information do not exist. The economically efficient levels of emissions, the carbon tax, and the permit price cannot be categorically determined. The targeted level of emissions is often proposed by non-economists. The spatial extent and time span of the emissions target need to be considered. The carbon tax is bound to be somewhat speculative, which does not bode well for private-sector decision-makers who have to adjust their behavior, and for the achievement of a particular emissions target.
The permit price depends on how permits are initially distributed and how well the permit market is designed. The effectiveness of either program is tied to monitoring and enforcement. Social justice considerations in the operation of tax programs often include the condition that they be revenue-neutral.
This is more complicated in the permit scheme as much activity after the initial phase is among the emitters themselves. Scenarios of the uncertain future continue to be generated under myriad assumptions in the quest for the most reliable. Deforestation: Drivers, Implications, and Policy Responses. Over the last 8, years, cumulative forest loss amounted to approximately 2. The rate of loss has slowed from 7.
Globally since the s, the net loss in the tropics has been outweighed by a net gain in the subtropical, temperate, and boreal climate zones. Deforestation is driven by a number of complex direct and indirect factors. Agricultural expansion both commercial and subsistence is the primary driver, followed by mining, infrastructure extension, and urban expansion.
In turn, population and economic growth drive the demand for agricultural, mining, and timber products as well as supporting infrastructure. This increase is unlikely to be offset entirely by agricultural intensification due to limits on yield increases and land quality.
Deforestation is also affected by other factors such as land tenure uncertainties, poor governance, low capacity of public forestry agencies, and inadequate planning and monitoring. Forest loss has a number of environmental, economic, and social implications.
Forests provide an expansive range of environmental benefits across local, regional, and global scales, including: hydrological benefits e. The long-term loss of forest resources also negatively affects societies and economies. The forest sector in contributed roughly 0.
About million people globally live in forest ecosystems, with an estimated million people entirely dependent on forest ecosystems for their livelihoods. Understanding how to best manage remaining forest resources in order to preserve their unique qualities will be a challenge that requires an integrated set of policy responses. Developing and implementing effective policies will require a better understanding of the socio-ecological dynamics of forests, a more accurate and timely ability to measure and monitor forest resources, sound methodologies to assess the effectiveness of policies, and more efficacious methodologies for valuing trade-offs between competing objectives.
Deforestation of the Brazilian Amazon. Deforestation in Brazilian Amazonia destroys environmental services that are important for the whole world, and especially for Brazil itself. The forest also maintains the human populations and cultures that depend on it. Deforestation rates have gone up and down over the years with major economic cycles. Government repression measures explain the continued decline from to , but an important part of the effect of the repression program hinges on a fragile base: a decision that makes the absence of pending fines a prerequisite for obtaining credit for agriculture and ranching.
Massive plans for highways, dams, and other infrastructure in Amazonia, if carried out, will add to forces in the direction of increased deforestation. Deforestation occurs for a wide variety of reasons that vary in different historical periods, in different locations, and in different phases of the process at any given location.
Economic cycles, such as recessions and the ups and downs of commodity markets, are one influence. The traditional economic logic, where people deforest to make a profit by producing products from agriculture and ranching, is important but only a part of the story. Ulterior motives also drive deforestation. Land speculation is critical in many circumstances, where the increase in land values bid up, for example, as a safe haven to protect money from hyperinflation can yield much higher returns than anything produced by the land.
Even without the hyperinflation that came under control in , highway projects can yield speculative fortunes to those who are lucky or shrewd enough to have holdings along the highway route. The practical way to secure land holdings is to deforest for cattle pasture.
This is also critical to obtaining and defending legal title to the land. In the past, it has also been the key to large ranches gaining generous fiscal incentives from the government. Deforestation receives impulses from logging, mining, and, especially, road construction. Soybeans and cattle ranching are the main replacements for forest, and recently expanded export markets are giving strength to these drivers.
Population growth and household dynamics are important for areas dominated by small farmers. Extreme degradation, where tree mortality from logging and successive droughts and forest fires replace forest with open nonforest vegetation, is increasing as a kind of deforestation, and is likely to increase much more in the future. Controlling deforestation requires addressing its multiple causes.
Repression through fines and other command-and-control measures is essential to avoid a presumption of impunity, but these controls must be part of a broader program that addresses underlying causes. The many forms of government subsidies for deforestation must be removed or redirected, and the various ulterior motives must be combated. Industry agreements restricting commodity purchases from properties with illegal deforestation or from areas cleared after a specified cutoff have a place in efforts to contain forest loss, despite some problems.
The notion that the — deforestation slowdown means that the process is under control and that infrastructure projects can be built at will is extremely dangerous. Finally, one must provide alternatives to support the rural population of small farmers. Large investors, on the other hand, can fend for themselves. Tapping the value of the environmental services of the forest has been proposed as an alternative basis for sustaining both the rural population and the forest.
Despite some progress, a variety of challenges remain. Ecological Effects of Environmental Stressors. Regimes of environmental stress are exceedingly complex. Particular stressors exist within continua of intensity of environmental factors. Those factors interact with each other, and their detrimental effects on organisms are manifest only at relatively high or low strengths of exposure—in fact, many of them are beneficial at intermediate levels of intensity.
Although a diversity of environmental factors is manifest at any time and place, only one or a few of them tend to be dominant as stressors. It is useful to distinguish between stressors that occur as severe events disturbances and those that are chronic in their exposure, and to aggregate the kinds of stressors into categories while noting some degree of overlap among them.
Climatic stressors are associated with extremes of temperature, solar radiation, wind, moisture, and combinations of these factors. They act as stressors if their condition is either insufficient or excessive, in comparison with the needs and comfort zones of organisms or ecosystem processes. Chemical stressors involve environments in which the availability of certain substances is too low to satisfy biological needs, or high enough to cause toxicity or another physiological detriment to organisms or to higher-level attributes of ecosystems.
Wildfire is a disturbance that involves the combustion of much of the biomass of an ecosystem, affecting organisms by heat, physical damage, and toxic substances. Physical stress is a disturbance in which an exposure to kinetic energy is intense enough to damage organisms and ecosystems such as a volcanic blast, seismic sea wave, ice scouring, or anthropogenic explosion or trampling.
Biological stressors are associated with interactions occurring among organisms. They may be directly caused by such trophic interactions as herbivory, predation, and parasitism. They may also indirectly affect the intensity of physical or chemical stressors, as when competition affects the availability of nutrients, moisture, or space. Extreme environments are characterized by severe regimes of stressors, which result in relatively impoverished ecosystem development.
This may be a consequence of either natural or anthropogenic stressors. As the world urbanizes, we need to study and understand the impacts of these changes to be able to live harmoniously with nature. For example, how much land should we designate as green space around streams that flow through subdivisions?
How do we prevent road pollution from dumping on baby fish at the next big rainfall? Urban ecologists work to find solutions to these problems. You can't physically travel to all of the places you wish to study. Even if you could, by the time you got there, the place would have already changed. In order to cover vast amounts of land, scientists are increasingly turning to tools like satellites and drones to spy on the natural world from afar.
They can then put the information they get on maps in a geographic information system GIS program and analyze the data. Scientists use GIS for many reasons, like tracking the greening of the Serengeti as the rainy season starts. Currently, there's a lot of work in "ground-truthing" the data — i. GIS skills are useful in an array of fields , such as city planning and engineering.
Another consequence of our quick industrialization over the past few hundred years is the increase in pollution and contamination. A lot of economic activity damages the environment, in some cases spreading heavy metals and even radioactive material into communities' drinking water. It's a big job to clean all of that up. But rather than shoveling dirt, what if you could spread microbes on the ground that would eat the pollution and neutralize it?
Bioremediation scientists do just that by engineering microbes to take care of some of humans' largest messes. You might not think noise could be a pollutant aside from rowdy neighbors when you're trying to study , but it is. In this newly emerging field, researchers attempt to understand how noisy environments can impact the organisms living within them.
For example, how does the roar of airports affect nearby wildlife? What happens if endangered orcas can't echolocate because of the noises from freighters carrying international cargo? How do ambient city noises subtly affect people trying to sleep? These are all critical questions those studying noise pollution are trying to answer. Scientists who study the ocean are called oceanographers , but one overlooked area is our world's freshwater.
Those who research freshwater are called limnologists, and they're playing an increasingly bigger role as we work to understand and mitigate our impacts on water ecosystems. Because freshwater bodies of water are much smaller than the ocean, there's more potential for things to go awry in them.
For example, if you dump a truck full of fertilizer into the ocean, it won't have much of an impact. But if you do the same in a lake, it could cause eutrophication, or the process of algae growing too fast and choking every other living thing out of the water.
Scientists estimate that between and 2, species go extinct each year. Extinction is a normal process, but humans have ramped up this rate to abnormally high levels. Our ecosystem depends on biodiversity, and to keep our environment healthy, we need to prevent animals from going extinct. It's not an easy job, and conservationists often find themselves on the losing end of the battle. But that doesn't mean we should stop. There's still a lot of opportunity to save endangered species and prevent existing species from becoming endangered in the first place.
At last, the world is waking up to the fact that people of color and other marginalized populations lack something many take for granted: a healthy environment. Not everyone has access to clean drinking water, good soil, clean air, and green spaces. And without these things, you can't live your life to its fullest potential. Right now there's a lot of research being done to quantify the extent of these problems.
How many people have been impacted by the Flint water crisis? What's happening to the widows of Navajo uranium miners? By documenting these impacts, we can work together toward a solution in this unique niche that blends environmental science with sociology.
We face more challenges today than we ever have before in making sure Earth stays habitable for future generations. As our population grows, environmental problems will become more pressing and require more drastic solutions and changes.