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Über dieses Buch

Roughly a billion people around the world continue to live in state of chronic hunger and food insecurity. Unfortunately, efforts to improve their livelihoods must now unfold in the context of a rapidly changing climate, in which warming temperatures and changing rainfall regimes could threaten the basic productivity of the agricultural systems on which most of the world’s poor directly depend. But whether climate change represents a minor impediment or an existential threat to development is an area of substantial controversy, with different conclusions wrought from different methodologies and based on different data.

This book aims to resolve some of the controversy by exploring and comparing the different methodologies and data that scientists use to understand climate’s effects on food security. In explains the nature of the climate threat, the ways in which crops and farmers might respond, and the potential role for public and private investment to help agriculture adapt to a warmer world. This broader understanding should prove useful to both scientists charged with quantifying climate threats, and policy-makers responsible for crucial decisions about how to respond. The book is especially suitable as a companion to an interdisciplinary undergraduate or graduate level class.



Part I


Chapter 1. Introduction

The Earth is clearly warming. Mounting evidence from around the globe has removed virtually any serious doubt over this fact, and also over whether the main culprit is human emissions of heat-trapping gases such as carbon dioxide (CO2). These emissions have been the product of a march towards better economic living standards, and for much of the world this march has led people out of a life of hunger and poverty and into one of relative comfort and security. But many have been left behind, and roughly 1 billion people continue to live under poverty and with insecure access to food. In an average day, more than 20,000 children die from hunger related causes.
A large majority of the world’s poor continue to live in rural areas and depend on agriculture for their livelihoods. Given that agriculture everywhere remains dependent on weather, changes in climate have the potential to disproportionally affect these poor populations. But what, precisely, will human-induced climate changes mean for the globe’s billion poor? How will climate change interact with the many other factors that affect the future of food production and food security?
There are no easy answers to these questions. That fact, of course, does not stop people from making simple predictions based on ideology, such as that innovation and free market responses will avoid any damages, or that climate change will wreak havoc on humans. Theory alone cannot refute either of these extreme positions, as there are no obvious reasons why that the pace of climate change caused by human activity should or should not match the pace with which we are able to adapt food production systems. Rather, the issue at hand is an empirical one, and finding answers will require a cadre of scientists capable of collecting and analyzing the relevant data, and policy makers and citizens capable of understanding their implications.
David Lobell, Marshall Burke

Chapter 2. Climate Effects on Food Security: An Overview

There are roughly 1 billion food insecure people in the world today, each having this status because food is unavailable to them, because it is unaffordable, or because they are too unhealthy to make use of it – or some combination of the three. Assessing the potential effects of climate change on food security requires understanding the underlying determinants of these three aspects of food security – availability, access, and utilization – and how climate change might affect each. This chapter explores these aspects and determinants of food security, summarizing the basic mechanisms by which climate change might impact the lives of the global food insecure.
Marshall Burke, David Lobell

Chapter 3. Climate Models and Their Projections of Future Changes

This chapter describes global climate models and their output. The current approaches for analyzing their simulations, characterizing the range of likely future outcomes, and making projections relevant for impact analysis are described, specifically referring to the latest assessment report of the Intergovernmental Panel on Climate Change. We provide a summary of future projections of average temperature and precipitation changes at continental scales, together with a broad brush picture of the likely changes in indices of extremes, characterizing both temperature and precipitation events. An analysis of changes in growing season length is also presented as an example of climate model output analysis directly relevant to studies of climate change impacts on food security.
Claudia Tebaldi, Reto Knutti

Part II


Chapter 4. Crop Response to Climate: Ecophysiological Models

To predict the possible impacts of global warming and increased CO2 on agriculture, scientists use computer-based models that attempt to quantify the best-available knowledge on plant physiology, agronomy, soil science and meteorology in order to predict how a plant will grow under specific environmental conditions. The chapter reviews the basic features of crop models with emphasis on physiological responses to temperature and CO2 and explains how models are used to predict potential impacts of climate change, including options for adaptation. The closing section reviews major issues affecting the reliability of model-based predictions. These include the need for accurate inputs, the challenges of improving the underlying physiological knowledge, and the need to improve representations of genetic variation that likely will affect adaptation to climate change.
Jeffrey W. White, Gerrit Hoogenboom

Chapter 5. Crop Responses to Climate: Time-Series Models

Time series of annual crop production levels, at scales ranging from experimental trials to regional production totals, are widely available and represent a useful opportunity to understand crop responses to weather variations. This chapter discusses the main techniques of building models from time series and the tradeoffs involved in the many decisions required in the process. A worked example using United States maize production is used to illustrate key concepts.
David Lobell

Chapter 6. Crop Responses to Climate and Weather: Cross-Section and Panel Models

Crop choices vary by climate, e.g., Florida specializes in citrus crops while Iowa specializes in corn and soybeans. The advantage of a cross-sectional analysis is that it incorporates how farmers adapt to existing difference in average climate conditions across space. A potential downfall is omitted variable bias. A panel analysis can overcome omitted variable bias by including fixed effects to capture all additive time-invariant influences, yet does not account for the same set of adaptation possibilities.
Wolfram Schlenker

Chapter 7. Direct Effects of Rising Atmospheric Carbon Dioxide and Ozone on Crop Yields

Rising atmospheric carbon dioxide concentration ([CO2]) in this century will alter crop yield quantity and quality. It is important to understand the magnitude of the expected changes and the mechanisms involved in crop responses to elevated [CO2] in order to adapt our food systems to the committed change in atmospheric [CO2] and to accurately model future food supply. Free-Air CO2 Enrichment (FACE) allows for crops to be grown in their production environment, under fully open air conditions, at elevated [CO2]. Current best estimates for the response of the staple crops wheat, soybean and rice from FACE experiments are that grain yield will increase by 13% at 550 ppm CO2. For the C4 species, sorghum and maize, grain yield is not expected to increase at elevated [CO2] if water supply is adequate. Grain quality is adversely affected by elevated [CO2]. On average, protein content decreases by 10–14% in non-leguminous grain crops and concentrations of minerals, such as iron and zinc decrease by 15–30%. While these represent our best estimate of changes in crop yield quantity and quality, most studies have been done in temperate regions, and do not account for possible interactions of rising [CO2] with other aspects of climate change, including increased temperature, drought stress and tropospheric ozone concentration.
Elizabeth A. Ainsworth, Justin M. McGrath

Part III


Chapter 8. Food Security and Adaptation to Climate Change: What Do We Know?

The potential for agricultural systems to adapt to climate change is at once both promising and poorly understood. This chapter reviews possible producer and consumer responses to a changing climate, the ability of these responses to offset otherwise negative impacts on food security, and the role of public and private institutions in investing in adaptation where individual responses are insufficient. Accumulated evidence suggests that wealthier societies and households will be better able to adapt to a changing climate because of their greater availability of alternatives and their ability to take advantage of them. Accordingly, investments that improve options for the poor, such as improved agricultural production technologies, financial instruments, and off-farm income opportunities, will likely be critical for adapting food security to a changing climate.
Marshall Burke, David Lobell

Chapter 9. Breeding Strategies to Adapt Crops to a Changing Climate

Climate change is expected to reduce global crop productivity, although the impact will vary region to region. At many locations, particularly those at lower latitudes, the environment will become drier and hotter, which will reduce crop yields and potentially change the incidence of insect pests and diseases. These climatic changes are also expected to alter the nutritional properties and processing quality of crop products. This chapter describes breeding approaches that may be employed to mitigate the effects of increased heat and drought in the crop production environment.
R. M. Trethowan, M. A. Turner, T. M. Chattha

Part IV


Chapter 10. Global and Regional Assessments

The main conclusions from recent global and regional assessments are reviewed, with an emphasis on China, India, Africa, and the United States. Most studies have provided primarily “best-guess” point estimates, often supplemented with a few sensitivity analyses, but without a comprehensive measure of uncertainties. Although some useful lessons have been learned, most existing estimates of food security risks leave much to be desired. We explore these estimates, some of their strengths and weaknesses, and some additional opportunities for measuring uncertainties.
David Lobell, Marshall Burke

Chapter 11. Where Do We Go from Here?

Some suggestions for future research on food availability, access, and utilization impacts of climate change are presented. Top priorities include better characterization of uncertainties in climate and crop responses, examining income responses to yield changes, and quantifying links between incomes, health, and food security. Many of these questions will require a more interdisciplinary approach than has been typical of past research.
David Lobell, Marshall Burke



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