Climate Variability in the Context of Climate Change: El Niño and Other Oscillations

The climate system envelops our planet, with swirling fluxes of mass, momentum, and energy through air, water, and land. Its processes are partly regular and partly chaotic. The regularity of diurnal and seasonal fluctuations in these processes is well understood. Recently, there has been significant progress in understanding some of the mechanisms that induce deviations from that regularity in many parts of the globe. These mechanisms include a set of combined oceanic–atmospheric phenomena with quasi-regular manifestations. The largest of these is centered in the Pacific Ocean and is known as the El Niño–Southern Oscillation. The term “oscillation” refers to a shifting pattern of atmospheric pressure gradients that has distinct manifestations in its alternating phases. In the Arctic and North Atlantic regions, the occurrence of somewhat analogous but less regular interactions known as the Arctic Oscillation and its offshoot, the North Atlantic Oscillation, are also being studied. These and other major oscillations influence climate patterns in many parts of the globe. Examples of other large-scale interactive ocean–atmosphere– land processes are the Pacific Decadal Oscillation, the Madden-Julian Oscillation, the Pacific/North American pattern, the Tropical Atlantic Variability, the West Pacific pattern, the Quasi-Biennial Oscillation, and the Indian Ocean Dipole. In this chapter we review the earth’s climate system in general, define climate variability, and describe the processes related to ENSO and the other major systems and their interactions. We then consider the possible connections of the major climate variability systems to anthropogenic global climate change. The climate system consists of a series of fluxes and transformations of energy (radiation, sensible and latent heat, and momentum), as well as transports and changes in the state of matter (air, water, solid matter, and biota) as conveyed and influenced by the atmosphere, the ocean, and the land masses. Acting like a giant engine, this dynamic system is driven by the infusion, transformation, and redistribution of energy.

Impacts of El Niño and La Niña Cycles: Systems and Sectors

Perturbations of the climate system caused by El Niño and La Niña events affect natural and managed systems in vast areas of the Pacific Ocean and far beyond it. (Other oscillations affect systems and sectors in wide swaths of the world as well.)1 El Niño–Southern Oscillation (ENSO) events have been associated with ecosystem disruptions and forest fires, crop failures and famines, disease epidemics, and even market fluctuations in various regions. The forms and degrees of impact depend not only on the strength and duration of an El Niño or La Niña event and its associated teleconnections, but also on the state, sensitivity, and vulnerability of the affected system and its biotic community, as well as its human population. The underlying characteristics of ecosystems and human societies in each region are important factors in their susceptibility to ENSO-related damages. Variation may be enhanced as ENSO effects ripple through natural and managed ecosystems. The underlying health of the affected biota, interrelationships among different biotic associations, and pressure by humans all affect marine as well as terrestrial ecosystem responses to ENSO events. Impacts on human systems can be both direct and indirect. Some ENSO phenomena, such as severe storms, affect human lives and infrastructures directly. Other impacts occur through alterations in the marine and terrestrial ecosystems and water supplies upon which human populations ultimately depend. In this chapter we consider some of the impacts that ENSO and other oscillations (described with their teleconnections in chapter 1) have on marine and terrestrial ecosystems and on human-managed systems apart from agriculture. The significant and geographically widespread changes that El Niño events induce in the Pacific Ocean alter conditions for various marine communities. These alterations include dramatic changes in the abundance and distribution of organisms, associated collapses of commercial fisheries, and ensuing consequences affecting human livelihood (Glantz, 2004; Lehodey et al., 2006). Some of the effects are well documented. Reductions in primary production of up to 95% were measured in the eastern equatorial Pacific in 1982–83 (Barber and Chavez, 1983.) Large changes in ecosystem structure and productivity have also been recorded in other parts of the Pacific Ocean, including the western Pacific and in the North Pacific subtropical gyre (north of the Hawaiian Islands) (Karl et al., 1995).

Analysis of El Niño Effects: Methods and Models

Knowledge of climate impacts is necessarily embedded in multifaceted, multiscaled contexts. The many facets include physical, ecological, and biological factors—as well as social, political, and economic ones—interacting on a spectrum of scales ranging from the individual to the household, the community, the region, the nation, and the world. Such complexities encompass natural as well as cultural aspects. Therefore, assessing the role of climate requires a comprehensive, integrated approach. Various methods and models have been proposed or developed to aid understanding of the relationships between agriculture and climate variability (and more specifically, ENSO) in regions around the world. Relevant methods include socioeconomic research techniques such as interviews and surveys; statistical analyses of climate and agronomic data; spatial analysis of remote-sensing observations; climate-scenario development with global and regional climate models and weather generators; and cropmodel simulations. Here we describe conceptual models that guide regional analysis, a framework of methods for regional studies, and examples of research in several agricultural regions that experience varying degrees of ENSO effects. Conceptual models are important because they can guide research and application projects and help physical, biological, and social scientists work together effectively within a common context. Equally important is the role of conceptual models in promoting effective interactions between researchers and agricultural practitioners. An early conceptual model for enhancing the usefulness of seasonal climate forecasts has been called the “end-to-end” approach (figure 5.1a). This model consists of a linear unidirectional trajectory in which El Niño events precipitate climate phenomena that, in turn, induce agronomic responses, with ensuing economic consequences. In disciplinary terms, the end-to-end trajectory begins with the physical sciences, proceeds to agronomy, and then to social science—primarily economics. The end-to-end model quickly evolved into an “end-to-multiple-ends” approach (figure 5.1b) because social science consists of many disciplines besides economics. Outcomes and insights regarding the use of seasonal climate forecasts differ, depending on whether the disciplines of economics, anthropology, political science, or sociology are involved. However, a weakness of these conceptual models is the absence of agricultural practitioners (e.g., farmers, planners, input providers, and insurers) in the research process.

Climate, Society, and Sustainable Development: Assessing Vulnerability, Building Adaptive Capacity

Agriculture and food security, water resources, ecosystems, natural disasters, and human health are all affected significantly by short-term fluctuations of weather and by longer-term changes of climate. Such effects can be severe enough to disrupt national and regional economies, particularly in developing countries, thus exacerbating poverty and thwarting sustainable development in both the short and long term. Developed and developing countries differ in their vulnerability to the effects of climate and in their capacity to recover from them. Developing countries are expected to be more vulnerable than developed countries to long-term climate change caused by the anthropogenic build-up of greenhouse gases. The challenge is to integrate climate adaptability into sustainable development effectively, so that detrimental effects are minimized and positive effects are enhanced. In this chapter we address the questions of how climate generally and El Niño specifically can affect sustainable development, consider the related concepts of vulnerability and adaptive capacity, and evaluate policies and programs designed to incorporate improved responses to climate variability and change into society. Sustainable development, a term brought to the attention of the world by the Bruntland Report, Our Common Future (United Nations Commission on Environment and Development, 1987), is a broad, often normative term used to describe a process by which developing countries are able to achieve economic growth comparable to the more developed countries without compromising environmental health and social equity. The report defines development as sustainable when it meets the needs of the present without compromising the ability of future generations to meet their own needs. Another simpler working definition that has been put forward is “development that lasts” (Magalhães, 2000, p. 4). Sustainable development is often characterized asmultidimensional, having economic, social, environmental, and political aspects (Magalhães, 2000). Economic sustainability is defined as the ability of programs to exist without long-term government incentives. Social sustainability relates to progress toward amelioration of poverty, income equality, and inclusiveness; whereas political sustainability involves shared participation in decision making and in stable institutions. Environmental sustainability involves the use of natural resources in a way that preserves or enhances their productivity, even while conserving habitats, biodiversity, and landscape.

Regional Activities in a Global Framework: Developing and Developed Countries

Regional studies and activities related to the El Niño–Southern Oscillation (ENSO) and other oscillations, seasonal climate prediction, and agricultural impacts are in progress around the world (figure 7.1). Here we describe some regional impacts and programs in place that are entraining climate information into decision making. Elements of these activities include the definition of the agricultural or other targeted systems; exploration of the social, political, and cultural contexts; examination of the temporal and spatial patterns of physical and biological impacts related to ENSO; analysis of economic effects; development and testing of seasonal climate forecasts and their delivery; investigation of crop management and other adaptations leading to implementation of dynamic risk-management strategies; and the development and evaluation of programs. In northern Peru, El Niño events bring torrential rains and floods that damage crops by eroding slopes, silting valleys, and oversaturating soils. The precipitation regime of Chile is likely to be intensified as well when El Niño events occur (Meza et al., 2003). Downscaled seasonal climate forecasts and crop growth models have been used to evaluate the impact of ENSO and management responses on crops in the Andean highlands of Peru (Baigorria, 2007); and Meza (2007) combined stochastic modeling of meteorological variables, a simple soil crop algorithm, and a mathematical programming model to assess the value of ENSO information for irrigation in the Maipo River Basin, Chile. Central America, being a narrow strip of land tightly squeezed between the Atlantic and Pacific oceans, is particularly influenced by major global climate variability systems, especially the El Nino–Southern Oscillation and the Arctic Oscillation (AO; M. Campos and P. Ramirez, personal communication, 2007; Rosenzweig et al., 2007). El Niño events are associated with dry summers on the Pacific coast and wet summers on the Caribbean coast, while the opposite pattern is associated with La Niña. A decrease in winter rainfall on the Caribbean coast since the late 1970s has been linked to changes in the Arctic Oscillation. Events with important economic and social consequences affected Central America in 1926, 1945–56, 1956–57, 1965, 1972–73, 1982–83, 1992–94, and 1997–98 (Ramirez, 2005).

Recent El Niños and Their Manifestations: Evolving Understanding

Since the 1970s, there has been a growing global awareness of the El Niño–Southern Oscillation (ENSO) phenomenon, especially in regard to its impacts on humans, natural ecosystems, and agriculture. The three strongest events of these decades (1972–73, 1982–83, and 1997–98) each marked a milestone in this progression. To be sure, not all climate extremes during any given ENSO year are necessarily due to that phenomenon; for example, the intense drought that occurred in 1982–83 in the West African Sahel does not appear to be causally linked to the strong ENSO event of that period (Glantz, 1987). However, even unrelated climate anomalies can exacerbate the effects of an El Niño or La Niña on world food supplies. Here we summarize the major effects of the three most recent very strong El Niño events (see box 4.1) with a focus on their agricultural manifestations. Table 4.1 summarizes the effects by region and continent and for the world food system as a whole. Evolving understanding of ENSO (and its related phenomena) appears to be contributing to the development of improved resilience to such major climate shocks in some regions (see chapter 6 for use of ENSO predictions in agriculture and chapter 8 on building adaptive capacity). However, continuing progress in affected regions is needed for agriculture to withstand (or benefit from) very strong El Niño events in the future, especially since global climate change may be affecting conditions as well. The El Niño of 1972–73 awakened international attention to the ENSO cycle. Besides the failure of the fishery industry in Peru, there were droughts, floods, and food shortages in various locations around the world that also appeared to be associated with El Niño. Consequently, scientists and the public began to realize that El Niño teleconnections and their impacts could extend beyond the West Coast of South America (Glantz, 2001). During the El Niño event of 1972–73, the reduced anchoveta harvest, combined with overfishing, caused the collapse of the Peruvian fishmeal industry and the dislocation of entire fishing communities.

Links to Agroecosystems: Processes and Productivity

The climate teleconnections related to El Niño–Southern Oscillation (ENSO) events described in chapter 1 have global implications regarding agriculture. In many locations, ENSO events appear to account for a significant part of the climate variability that governs the responses of crops and livestock on a range of temporal and spatial scales. Teleconnections affect variations in production both within growing seasons and from one season or year to another. Precipitation, temperature, and other climate variables are key determinants of crop growth and livestock health, affecting all aspects of agroecosystems, including the survival and reproduction of both beneficial and damaging insects. An understanding of ENSO teleconnections may help farmers and regional planners assess changes in probable yield levels before the growing season and thus provide guidance for improved management. In this chapter we introduce agricultural responses to climate extremes in general and to ENSO climate teleconnections in particular. Subsequent chapters describe methods of analysis, use of ENSO predictions for agriculture, and regional aspects in more detail. Variability in agricultural production affects risk on at least five levels: individual farms, farming regions within nations, nations, groups of nations, and the global food system. Contributing factors and consequences of variability at successive levels differ in type and scale. Perhaps the most relevant example of these differences is the contrast between the effect of variability on a single farm and its effect at the national level for any country in which the agricultural sector plays a significant role in the overall economy. At the individual farm level, the aim is generally to produce high yields as consistently as possible. Hence, the main concern regarding climate is the occurrence of seasons with low yield levels that threaten subsistence or income. When regional or national yields are very low, overall food security may be threatened, necessitating relief efforts by donor countries and agencies. At the national level, however, problems may be caused not only by low yields but also by the opposite—unusually high yields. Whereas low national yields may cause food shortages and high food prices, high overall yields tend to lower commodity prices paid to farmers and create excessive surpluses that necessitate government intervention. High variability in food production at the national level thus can destabilize domestic prices, farm income, and national budgets.

Seasonal Climate Predictions: Farmers, Planners, and Policymakers

Researchers from the physical, biological, and social sciences, in communication with decision-makers, are working to improve and apply seasonal climate forecasts relevant to risk management in climate-sensitive systems. Noteworthy is the mission of the International Research Institute for Climate and Society (IRI), which focuses on integrating the roles of science and society to forecast climate phenomena in general, and the El Niño–Southern Oscillation (ENSO) in particular. The National Oceanic and Atmospheric Administration created IRI in 1996 at Columbia University in New York to engage in climate research and modeling on the seasonalto- interannual time scale and to provide the results of the research to people affected by climate in various regions of the world. Agrawala et al. (2001) characterize the IRI as a “boundary” institution, straddling two major divides: one between fundamental research and societal applications, and the other between developed and developing countries. The motivations for its creation included fostering a multidisciplinary approach to applications, building on current programs and policies, and redressing inequity in large-scale climate research. Farmers and other agricultural decision-makers are a major group of potential users of seasonal climate forecasts. Water-resource managers are another such group. Interdisciplinary efforts have deepened the realization that improved climate information systems are embedded in social, economic, and political contexts and that understanding these contexts is required in order to improve the use of forecasts. A key aspect of the context of climate forecasting is the interrelationship of climate, climate forecasts, and risk. A growing body of research pertains to how agricultural decision-makers relate to risk and how responding to climate forecasts may help them manage it. This research is in the process of being consolidated into a framework by which forecasts can be made, disseminated, and utilized effectively by a range of decision-makers. Questions relevant to the use of climate predictions include: How can agricultural practitioners at different levels of social organization use climate forecasts to improve their planning and management decisions? How are climate risks perceived and acted on? What are the potential economic benefits? What policies can facilitate the use of climate-forecast information?