For several decades, the Sahelian countries have been facing continuing rainfall shortages, which, coupled with anthropogenic factors, have severely disrupted the great ecological balance, leading the area in an inexorable process of desertification and land degradation. The Sahel faces a persistent problem of climate change with high rainfall variability and frequent droughts, and this is one of the major drivers of population’s vulnerability in the region. Communities struggle against severe land degradation processes and live in an unprecedented loss of productivity that hampers their livelihoods and puts them among the populations in the world that are the most vulnerable to climatic change. In response to severe land degradation, 11 countries of the Sahel agreed to work together to address the policy, investment, and institutional barriers to establishing a land-restoration program that addresses climate change and land degradation. The program is called the Pan-Africa Initiative for the Great Green Wall (GGW). The initiative aims at helping to halt desertification and land degradation in the Sahelian zone, improving the lives and livelihoods of smallholder farmers and pastoralists in the area and helping its populations to develop effective adaptation strategies and responses through the use of tree-based development programs. To make the GGW initiative successful, member countries have established a coordinated and integrated effort from the government level to local scales and engaged with many stakeholders. Planning, decision-making, and actions on the ground is guided by participation and engagement, informed by policy-relevant knowledge to address the set of scalable land-restoration practices, and address drivers of land use change in various human-environmental contexts. In many countries, activities specific to achieving the GGW objectives have been initiated in the last five years.
Climate change adaptation is the ability of a society or a natural system to adjust to the (changing) conditions that support life in a certain climate region, including weather extremes in that region. The current discussion on climate change adaptation began in the 1990s, with the publication of the Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC). Since the beginning of the 21st century, most countries, and many regions and municipalities have started to develop and implement climate change adaptation strategies and plans. But since the implementation of adaptation measures must be planned and conducted at the local level, a major challenge is to actually implement adaptation to climate change in practice. One challenge is that scientific results are mainly published on international or national levels, and political guidelines are written at transnational (e.g., European Union), national, or regional levels—these scientific results must be downscaled, interpreted, and adapted to local municipal or community levels. Needless to say, the challenges for implementation are also rooted in a large number of uncertainties, from long time spans to matters of scale, as well as in economic, political, and social interests. From a human perspective, climate change impacts occur rather slowly, while local decision makers are engaged with daily business over much shorter time spans. Among the obstacles to implementing adaptation measures to climate change are three major groups of uncertainties: (a) the uncertainties surrounding the development of our future climate, which include the exact climate sensitivity of anthropogenic greenhouse gas emissions, the reliability of emission scenarios and underlying storylines, and inherent uncertainties in climate models; (b) uncertainties about anthropogenically induced climate change impacts (e.g., long-term sea level changes, changing weather patterns, and extreme events); and (c) uncertainties about the future development of socioeconomic and political structures as well as legislative frameworks. Besides slow changes, such as changing sea levels and vegetation zones, extreme events (natural hazards) are a factor of major importance. Many societies and their socioeconomic systems are not properly adapted to their current climate zones (e.g., intensive agriculture in dry zones) or to extreme events (e.g., housing built in flood-prone areas). Adaptation measures can be successful only by gaining common societal agreement on their necessity and overall benefit. Ideally, climate change adaptation measures are combined with disaster risk reduction measures to enhance resilience on short, medium, and long time scales. The role of uncertainties and time horizons is addressed by developing climate change adaptation measures on community level and in close cooperation with local actors and stakeholders, focusing on strengthening resilience by addressing current and emerging vulnerability patterns. Successful adaptation measures are usually achieved by developing “no-regret” measures, in other words—measures that have at least one function of immediate social and/or economic benefit as well as long-term, future benefits. To identify socially acceptable and financially viable adaptation measures successfully, it is useful to employ participatory tools that give all involved parties and decision makers the possibility to engage in the process of identifying adaptation measures that best fit collective needs.
Worldwide, governments subsidize agriculture at the rate of approximately 1 billion dollars per day. This figure rises to about twice that when export and biofuels production subsidies and state financing for dams and river basin engineering are included. These policies guide land use in numerous ways, including growers’ choices of crop and buyers’ demand for commodities. The three types of state subsidies that shape land use and the environment are land settlement programs, price and income supports, and energy and emissions initiatives. Together these subsidies have created perennial surpluses in global stores of cereal grains, cotton, and dairy, with production increases outstripping population growth. Subsidies to land settlement, to crop prices, and to processing and refining of cereals and fiber, therefore, can be shown to have independent and largely deleterious effect on soil fertility, fresh water supplies, biodiversity, and atmospheric carbon.
Kimberly M. Carlson and Rachael D. Garrett
Oil crops play a critical role in global food and energy systems. Since these crops have high oil content, they provide cooking oils for human consumption, biofuels for energy, feed for animals, and ingredients in beauty products and industrial processes. In 2014, oil crops occupied about 20% of crop harvested area worldwide. While small-scale oil crop production for subsistence or local consumption continues in certain regions, global demand for these versatile crops has led to substantial expansion of oil crop agriculture destined for export or urban markets. This expansion and subsequent cultivation has diverse effects on the environment, including loss of forests, savannas, and grasslands, greenhouse gas emissions, regional climate change, biodiversity decline, fire, and altered water quality and hydrology. Oil palm in Southeast Asia and soybean in South America have been identified as major proximate causes of tropical deforestation and environmental degradation. Stringent conservation policies and yield increases are thought to be critical to reducing rates of soybean and oil palm expansion into natural ecosystems. However, the higher profits that often accompany greater yields may encourage further expansion, while policies that restrict oil crop expansion in one region may generate secondary “spillover” effects on other crops and regions. Due to these complex feedbacks, ensuring a sustainable supply of oil crop products to meet global demand remains a major challenge for agricultural companies, farmers, governments, and civil society.
Towns and cities generally exhibit higher temperatures than rural areas for a number of reasons, including the effect that urban materials have on the natural balance of incoming and outgoing energy at the surface level, the shape and geometry of buildings, and the impact of anthropogenic heating. This localized heating means that towns and cities are often described as urban heat islands (UHIs). Urbanized areas modify local temperatures, but also other meteorological variables such as wind speed and direction and rainfall patterns. The magnitude of the UHI for a given town or city tends to scale with the size of population, although smaller towns of just thousands of inhabitants can have an appreciable UHI effect. The UHI “intensity” (the difference in temperature between a city center and a rural reference point outside the city) is on the order of a few degrees Celsius on average, but can peak at as much as 10°C in larger cities, given the right conditions. UHIs tend to be enhanced during heatwaves, when there is lots of sunshine and a lack of wind to provide ventilation and disperse the warm air. The UHI is most pronounced at night, when rural areas tend to be cooler than cities and urban materials radiate the energy they have stored during the day into the local atmosphere. As well as affecting local weather patterns and interacting with local air pollution, the UHI can directly affect health through heat exposure, which can exacerbate minor illnesses, affect occupational performance, or increase the risk of hospitalization and even death. Urban populations can face serious risks to health during heatwaves whereby the heat associated with the UHI contributes additional warming. Heat-related health risks are likely to increase in future against a background of climate change and increasing urbanization throughout much of the world. However, there are ways to reduce urban temperatures and avoid some of the health impacts of the UHI through behavioral changes, modification of buildings, or by urban scale interventions. It is important to understand the physical properties of the UHI and its impact on health to evaluate the potential for interventions to reduce heat-related impacts.
Christiane W. Runyan and Jeff Stehm
Over the last 8,000 years, cumulative forest loss amounted to approximately 2.2 billion hectares, reducing forest cover from about 47% of Earth’s land surface to roughly 30% in 2015. These losses mostly occurred in tropical forests (58%), followed by boreal (27%) and temperate forests (8%). The rate of loss has slowed from 7.3 Mha/year between 1990–2000 to 3.3 Mha/year between 2010–2015. Globally since the 1980s, 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. Population growth and changing consumer preferences, for instance, will increase global food demand 50% by 2050, possibly requiring a net increase of approximately 70 million ha of arable land under cultivation. 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.g., regulating water supply and river discharge), climate benefits (e.g., precipitation recycling, regulating local and global temperature, and carbon sequestration), biogeochemical benefits (e.g., enhancing nutrient availability and reducing nutrient losses), biodiversity benefits, and the support of ecosystem stability and resiliency. The long-term loss of forest resources also negatively affects societies and economies. The forest sector in 2011 contributed roughly 0.9% of global GDP or USD 600 billion. About 850 million people globally live in forest ecosystems, with an estimated 350 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.
Bradley Skopyk and Elinor G. K. Melville
The onset of Spanish imperial rule in Mexico in 1521 had profound consequences well beyond the political and cultural spheres. It also altered Mexico’s environment, reconstituting the region’s ecology as new fauna, flora, and microorganisms were added and as the population dynamics of native Mexican biota fluctuated in response to Old World arrivals. While the consequences of myriad interactions between native and non-native species were vast and complex, it was the decimation of indigenous persons by pathogens that was one of the first biological consequences of colonization (in fact, occurring first in 1520, one year before the fall of the Aztec state) and one of the most important. Mexican human populations were reduced by 80 to 90 percent, effecting cascading ecological consequences across the physical and biological geography of Mexico. Forests regenerated, terraced slopes degraded, and much of the Mexican landscape lost its anthropogenic aspect. Simultaneously, ungulate introductions transformed Mexican flora and likely initiated soil erosion in some regions that, when transported to fluvial environments, disrupted the flow of rivers. On the other hand, pigs, sheep, goats, horses, and other ungulates altered plant communities through selective seed dispersion. New economic pursuits such as brick making and silver mining increased demand for heat energy that, in an unprecedented manner, encouraged intensive forest usage and, probably, regional deforestation, although empirical data on historical forest cover are still lacking. Severe climate variability, of a scale not experienced for at least five hundred years and perhaps many millennia, occurred simultaneously with colonial-induced ecological change. A significant conquest-era drought was followed by one of the coolest and wettest periods of the Holocene; a strong pluvial in the Mexican context lasted from 1540 to around 1620. Subsequent anomalies of both temperature (cold) and precipitation (either wet or dry) occurred in the 1640s and 1650s, and from the 1690s until about 1705. Together, these climate anomalies are known as the core Little Ice Age, and initiated agrarian transitions, hazardous flooding, prolonged droughts, epidemics, epizootics, and recurring agrarian crises that destabilized human health and spurred high rates of mortality. Soil degradation and suppressed forest cover are also likely outcomes of this process. Although debate abounds regarding the timing, extent, and causes of soil and water degradation, there is little doubt that extensive degradation occurred and destabilized late-colonial and early-Republic societies.