Indirect effects of global climate change and the impact of extreme weather events on the German food system

TABLE OF CONTENTS

ABSTRACT

LIST OF FIGURES

LIST OF TABLES

LIST OF ABBREVIATIONS

1 Introduction
1.1 Significance and Aim of the study
1.2 Research Methods

2 State of the Art
2.1 Food systems and food security: concepts, relationships and trends
2.1.1 Food systems and food security
2.1.2 Globalization of our food systems
2.2 Observed and projected climatic changes
2.2.1 Climate change and global warming
2.2.2 Climate variability and extreme weather events
2.2.3 Global climate change projections
2.3 Direct impacts of climate change on food production
2.3.1 Sensitivity of agricultural production to climate change
2.3.2 Long-term effects of climate change
2.3.3 Short-term effects of climate variability and extreme events
Extreme temperatures
Drought
Heavy rainfall and flooding
Tropical storms

3 Indirect effects of climate change on food systems
3.1 Terminology and concept of the indirect effects of climate change
3.2 Transmission of climate change impacts across borders
3.2.1 Infrastructure
3.2.2 Finance
3.2.3 People
3.2.4 Trade
3.3 Transmission of climate change impacts along food systems via trade Case study: indirect effects of the Russian heatwave
3.4 Vulnerability to the indirect impacts of climate change

4 Exposure of the German food system to the indirect effects of climate change
4.1 Structure of the German food system
4.2 Agricultural commodity-import dependency
4.2.1 Soybeans
4.2.2 Palm oil
4.2.3 Bananas
4.2.4 Coffee
4.3 Vulnerability of the major German trading partners Case study: Brazil – soybeans

5 Results
5.1 Direct impacts of climate change on food production
5.2 Indirect impacts of climate change on food systems
5.3 Exposure of the German food system to the indirect effects of climate change

6 Discussion

7 Conclusion

8 References

9 Declaration

LIST OF FIGURES

Figure 1: Observed change in surface temperature from 1901-2012.

Figure 2: The effect of changes in temperature distribution on climate-related extreme events.

Figure 3: Global impacts of climate change on crop productivity by 2050.

Figure 4: Estimated impact of past climate trends (1980–2008) on crop yields for major producing countries and for global production.

Figure 5: Relationship between annual rainfall variability expressed as the 12-month Weighted Anomaly of Standardized Precipitation (WASP) and changes in gross domestic product (GDP) and agricultural gross domestic product (Ag GDP) in Niger from 1982 to 2003.

Figure 6: Interrelations between natural systems, human systems and coupled human and natural systems over distances.

Figure 7: Transmission pathway of climate change impacts between two distant locations.

Figure 8: Major human-made pathways of long-distance, indirect climate change impacts for Germany.

Figure 9: Key components for the transmission of climate change impacts between two distant locations along food systems via trade.

Figure 10: Global top five importing countries of wheat in 2010/11.

Figure 11: Vulnerability panels for supply shocks in (A) wheat, (B) maize, and (C) rice.

Figure 12: Global climate change effects on the agricultural productivity of the main German trading partners by 2050.

LIST OF TABLES

Table 1: Trends in food systems: differences between the past "old" and the modern "new" food system.

Table 2: Major climate-related loss events from the past decades.

Table 3: Median estimates of global temperature and precipitation trends (1980–2008) on average yields for maize, rice, wheat, and soybean.

Table 4: Major German import and export merchandise products in 2015.

Table 5: Major German agricultural commodity imports in 2013.

Table 6: Vulnerability of the major German suppliers of agricultural commodities from outside of Europe.

LIST OF ABBREVIATIONS

Abbildung in dieser Leseprobe nicht enthalten

ABSTRACT

The long-term reduction of hunger has recently slowed down as a result of ongoing global climate change, increasing climate variability, and extreme weather events, disrupting our global food system. The direct impacts of climate change in Germany are expected to be comparably low and the ability to adapt to these impacts is high. However, it is likely that Germany, as part of a highly interconnected world, may become increasingly affected by climate change impacts in other world regions. This thesis investigates how adverse effects of global climate change can be transferred across borders to demonstrate the various potential indirect impacts of climate change and extreme weather events on food systems. Moreover, this study seeks to assess how far the direct effects on agricultural productivity abroad and the disruption of transportation-related infrastructures can affect the German food system to depict its level of exposure to the indirect effects of global climate change via trade of agricultural commodities. The results show that Germany is heavily dependent on the import of soybeans, palm oil, bananas, and coffee from increasingly vulnerable trading partners outside of Europe. The direct impact on the production of these commodities represents a significant threat to the German food system via trade. The evidence suggests that improved understanding of the indirect impacts of climate change on food systems is needed to be able to adapt to the full range of risks from climate change, climate variability and extreme events on agricultural production.

Keywords: Climate change, extreme weather events, climate change impacts, transmission pathways, indirect effects, agricultural productivity, food systems, trade

1 Introduction

There is a long list of problems arising from a rapidly changing climate, however, the risks to world agriculture and the achievement of future food security is among the greatest challenges of our time. Depletion of scarce resources, land cover change, changes in the hydrological cycle and the availability of fertile soils are, among others, the major environmental challenges impacting on the global food production (Adger et al., 2009). Although great effort has been made in the last decades, the long-term reduction of hunger has recently slowed down as a result of increasingly volatile food prices, extreme weather events, and ongoing global climate change, disrupting our global food system (Wheeler & von Braun, 2013). Additionally, the world population is projected to reach 9.7 billion by 2050, with the largest increase in Africa and Asia, and a further accumulation of wealth in the developing world (UN, 2015). This, in turn, leads to a greater demand for food, often associated with a higher demand for meat products, and consequently to a higher demand for fodder. As a result, the Food and Agriculture Organization of the United Nations (FAO) estimates that the overall demand for food will increase by at least 60% until 2050 (FAO, 2016). Subsequently, carbon dioxide levels will continue to rise, followed by growing global mean temperatures and an increase in the frequency and intensity of extreme weather events (IPCC, 2012).

The direct impacts of climate change are expected to be unevenly distributed around the globe. Changing temperature and precipitation patterns will cause a shift of ecozones, leading to a global redistribution of agricultural potential, thereby posing a severe risk to national food systems (Müller et al., 2009). However, compared to the impacts of climate change in many other parts of the world, the direct impacts in Germany will be quite low, and the ability to adapt to these impacts is high (Adelphi/PRC/EURAC, 2015). Yet, most recent studies suggest that it is very likely that Germany will become increasingly exposed to the indirect effects of climate change, imported from distant countries (Benzie et al., 2016; Bren d’Amour et al., 2016; EEA, 2017). That means, Germany, as part of a highly interconnected world, may become increasingly affected by climate change impacts in other world regions, transferred to Germany via multiple pathways such as trade, migration of people, the flow of capital, or other aspects of globalization (EEA, 2017).

Particularly, the German food system rests on international trade and is increasingly dependent on the import of agricultural commodities for food and feed. At the same time, climate change is expected to reduce the yields of many crops worldwide, and is therefore projected to alter the global pattern and balance of food trade (Wheeler & von Braun, 2013). Nonetheless, present analyses on the impacts of climate change on food systems mainly focus on the effects of changing regional temperature and precipitation patterns on national crop yields, reflecting the direct nature of climate impacts. However, this strategy fails to acknowledge the many interconnections and interdependencies among and between countries and regions via trade (Bren d’Amour et al., 2016). The global food exports have increased tenfold since the early 1960s (Steinfeld, 2010), and the production and consumption of food are becoming increasingly detached, leading to a growing reliance of many countries on food imports and trade (Fader et al., 2013). As a result, no country exists in isolation, and the impacts and risks of climate change can be transferred across borders, challenging the security of our global and national food systems (Moser & Hart, 2015).

1.1 Significance and Aim of the study

There is a broad range of studies on the direct effects of climate change on agricultural productivity since already today many countries have been negatively affected by the impact of climate change, variability and an increasing number of extreme weather events. However, the international dimension of climate change impacts and the potential pathways for their transmission have not sufficiently been studied. Existing literature points to a large research gap in this field, as national adaptation strategies usually focus on the local impacts of climate change and tend to ignore the globalized structure of our food systems (Liverman, 2016). In fact, many climate impacts need to be approached on a larger scale to account for the global context of climate change and its far-reaching effects. Moreover, most recent studies suggest that especially import-dependent countries are becoming increasingly vulnerable to the indirect effects of climate change (Adelphi/PRC/EURAC, 2015; Benzie et al., 2016; Cerveny et al., 2014). Therefore, this study seeks to raise awareness of the concept of indirect effects of climate change, likely to become increasingly important for the German food system in the near future.

The overall objective of this master thesis is to investigate how and to what extent the negative effects of climate change and the impact of extreme weather events abroad can affect the German food system. Thereby, this study seeks to advance the understanding of the concept of indirect effects of climate change and to investigate the underlying mechanisms responsible for the transmission of adverse climate change effects across borders.

Thereof, the following specific objectives arise:

I. To describe the direct impacts of climate change and extreme weather events on agricultural productivity abroad.

II. To systematically analyse the concept of indirect effects of climate change.

III. To evaluate the structure of the German food system to examine its potential level of exposure to the indirect effects of climate change via trade.

Hypothesis:

The more dependent a country is on the import of agricultural commodities from vulnerable trading partners abroad, the more exposed it is to the indirect effects of climate change.

1.2 Research Methods

This research is primarily based on an extensive literature study. A systematic review identifies and synthesizes the most relevant yield impact studies to give an overview of the most prominent direct effects of climate change on food production. Thereafter, the outcome is combined with an analysis of the structure of the German food system, to translate the direct impacts of climate change on food production abroad into the indirect impacts of climate change on the German food system. Hereby, the study tries to exemplary investigate the level of exposure, as part of the vulnerability concept, of globalized food systems to the indirect effects of climate change. While in most previous climate change assessments the concept of vulnerability has been used as a measure of choice, this investigation prefers to use only part of the concept to avoid additional layers of complexity and to not exceed the scope of this thesis. Moreover, the concept is often used in the context of developing countries, to describe a system’s particular state of marginality and powerlessness to the adverse effects of climate change. Examining the level of vulnerability of the German food system could therefore mislead people in underestimating the magnitude of the indirect effects, as previous studies have demonstrated Germany’s comparably low level of sensitivity to climate change impacts and its overall high capacity to adapt (Adelphi/PRC/EURAC, 2015).

2 State of the Art

There are many potential impacts of climate change and extreme weather events on food systems. The purpose of this chapter is to give a critical overview of the existing literature on the highly interrelated fields of food systems, food security, and climate change and to position this study in the broader field of research. This section defines some general, but essential concepts because varying definitions are used in different fields of academia.

In particular, this section aims to provide an overview of the global food situation in times of global warming, with a focus on the long and short-term effects of climate change on agricultural productivity. The information given here serves as the basis for the specific analysis of the adverse indirect effects of climate change on the German food system later in this text. In addition, this section tries to link the existence of climate change and the increasing number of extreme weather events and its consequences for social and environmental systems to the influence of human activities and global change as the foundation for the transmission of the indirect impacts of climate change involve the influence of people.

2.1 Food systems and food security: concepts, relationships and trends

2.1.1 Food systems and food security

Today almost 2 billion people are food insecure of which almost 800 million are undernourished (FAO, IFAD, & WFP, 2015). Paradoxically, more than enough food is currently produced per capita to feed the world population (FAO et al., 2015). Almost all of the undernourished people live in the developing world, with the largest share of people living in Asia (510 million) and Africa (230 million) (FAO et al., 2015). Yet, it is important to note that these numbers are just a rough estimate, deficient in capturing all of the four pillars of food security: availability, access, utilization, and stability.

The concept of food security is very broad and various definitions exist that have been modified over time. Many earlier definitions focused on food production, whereas current definitions, adapted by the Committee on World Food Security (CFS) and the FAO put the socio-economic aspect in the centre, keeping with the 1996 World Food Summit definition (FAO, 1996) by stressing access to food:

“Food security exists when all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life...” (CFS, 2015).

Climate change and food security have many interrelated risks to societies and the environment, however, the methods used to measure the status of food security and the number of food insecure people in the world have serious deficiencies. First, these estimates are derived from aggregate data, not from actual household food shortages, which impedes the analysis of distributional effects of climate change (Wheeler & von Braun, 2013). Second, they only capture long-term trends and are not able to capture short-term changes, essential for examining the impacts of climate variability, extreme weather events or other short-term shocks on food production as an integral part of the global food system (Wheeler & von Braun, 2013).

There is a broad range of literature on food systems from different fields in academia that bring multiple perspectives and world views to light. Nonetheless, the most useful conceptualizations are those that define a food system as a string of activities ranging from production to consumption, including the multiple transformations of food that these steps entail and the food security outcomes of the respective activities. The most recent definition from the Fifth Assessment Report (AR5) of the United Nations Intergovernmental Panel on Climate Change (IPCC) goes as follows:

“A food system includes all processes and infrastructure involved in satisfying a population’s food security: gathering, growing, harvesting, processing, packaging, marketing, transporting, consuming of food, and disposing of food waste” (Porter et al., 2014).

In other words, the food security status of any population can be considered as the outcome of its food system (Ericksen, 2007). Hence, increases in the productivity and efficiency of food systems help to reduce hunger, whereas external threats and disruptions that decrease the productivity and efficiency, reduce food security.

As the concept of food security and food systems are so tightly coupled, food systems must be understood as more than just the single processes ranging from production through to consumption. Both food systems and food security are fundamentally determined by social, economic, and environmental change (Porter et al., 2014).

2.1.2 Globalization of our food systems

Food systems and agriculture have changed tremendously since the middle of the last century. During the green revolution, occurring between the 1930s and 1960s, agricultural development has seen a rapid advance, leading to a significant increase in yields due to increased irrigation and high levels of agricultural inputs.

The globalization of the food system began 30 years later, in the 1990s, mainly as a consequence of fast technological improvements, profoundly changing the way we produce and trade agricultural products. Here, globalization can be understood as “the erosion of barriers of time and space” that constrain the movement of goods, services and capital across borders (Byrnea & Glover, 2002), leading to an increased flow of commodities, technologies, information, financial capital, and new ways of distribution and marketing (FAO, 2004). Among other factors, including urbanization, the main drivers of these changes over the past decades were increased income and strong efforts to liberalize international trade, associated markets and investment flows (Kearney, 2010). As a consequence, there are several significant differences in the organization of the modern food system and the traditional food system. First, as distribution networks have expanded and transportation routes have improved, today, food travels very long distances before it gets consumed. As a result of this “spatial decoupling of production and consumption”, many countries become increasingly dependent on external resources and trade (Fader et al., 2013). Second, the foundation of the value chain has changed, as farming is no longer the main economic activity but the processing and packaging of raw materials into food products (Ericksen, 2007). Third, the overall income growth since the 1990s has led to a dietary transition, with an increasing demand for resource-intensive meat and dairy products, especially in the developing world. This, in turn, has led to a rising demand for the amount of grains, as 30-50% of the global production is fed to livestock (Tscharntke et al., 2012). Today, around 75% of the calories that humans directly or indirectly consume come from only four crops: maize, wheat, rice, and soybeans (D. B. Lobell, Schlenker, & Costa-Roberts, 2011), mainly produced in a handful of countries. In fact, the top five exporters of globally traded grains account for more than two-third of the total export volume (Bren d’Amour et al., 2016).

The environmental concerns over the globalization of our food systems, in particular, the industrialization and intensification of agricultural production systems are numerous. The FAO reports are consistent in calling the current growth in agricultural production unsustainable (FAO, 2008, 2016; FAO, IFAD, & WFP, 2012). Major trends of modern food systems lead to increasing demands of water for irrigation, an increase of pollution from agricultural inputs and large increases in energy demand. The outcome of this development is particularly dangerous as the impact of food systems on the environment create negative feedback loops that strengthen the risk posed to food systems by global environmental and climate change (Ericksen, 2007). Some of the major trends in modern food systems are summarized in Table 1.

Table 1: Trends in food systems: differences between the past "old" and the modern "new" food systems.

Abbildung in dieser Leseprobe nicht enthalten

Source: Maxwell & Slater (2003); adapted from Ericksen (2007).

2.2 Observed and projected climatic changes

2.2.1 Climate change and global warming

The patterns of observed and predicted climate change are well documented and reviewed by the Intergovernmental Panel on Climate Change (IPCC, 2013). The global mean temperature has risen by 0.85°C since preindustrial times, with plenty of temperature records being broken over land and sea in the past years (IPCC, 2013). However, averaging the temperature increase on a global scale masks the differences between land and sea, as well as differences between high and low latitudes.

An overview of the observed surface temperature change from 1901 to 2012 is given in Figure 1. The map is derived from temperature trends determined by linear regression of the combined land-surface air temperature (LSAT) and sea-surface temperature (SST) data set MLOST (see Vose et al., 2012). Clearly, there are large differences in changes of mean temperatures, not only between the land and the sea but also between continents, countries, and regions.

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Figure 1: Observed change in surface temperature from 1901-2012. The map is derived from temperature trends determined by linear regression of the combined land-surface air temperature (LSAT) and sea-surface temperature (SST) dataset NCDC MLOST. Trends have only been calculated where robust data was available; other areas are white. Grid boxes where the trend is significant are indicated by a + sign. Source: IPCC (2013).

Since 1950, the average temperatures have risen by about 0.13°C per decade, above all, driven by the emission of greenhouse gases (IPCC, 2013). CO2 levels have increased from about 315 parts per million (ppm) in 1958 to over 400 ppm today (US Department of Commerce, 2017). The sharp increase of such anthropogenic greenhouse gases can be attributed to the economic growth of a rising population. In 2010, the total anthropogenic emissions reached a record high of almost 50 gigatonnes of CO2 equivalent per year (IPCC, 2014b). Vermeulen et al. (2012) estimated that almost 30% of the total greenhouse gas emissions come from food system activities alone. The largest share of these emissions come from agriculture, while the rest originates from preproduction, mainly fertilizer manufacture, and postproduction activities like processing, packaging, and transport (Vermeulen, Campbell, & Ingram, 2012). However, the share of emissions from agriculture in main producing regions of raw materials is notably higher than in import-dependent countries that generate a larger proportion of their emissions from postproduction activities (ibid.).

2.2.2 Climate variability and extreme weather events

A changing climate not only leads to an increase of the global mean temperature and variability, but in turn, also to changes in the intensity, frequency, duration and spatial extent of extreme weather events (IPCC, 2012). There is a growing body of literature on climate-related extreme events, as the public and scientific awareness of the rising intensity and frequency of such events is increasing.

According to the Munich Re, one of the world’s largest reinsurance companies, the number of significant weather-related extremes per year, with at least one fatality and/or normalized losses ³100 000, 300 000, 1 million, or 3 million US$, depending on the income group of the affected country, has quasilinearly tripled from around 200 events to nearly 600 events in the last three decades (Munich Re, 2017). A list of the major climate-related loss events from the past years is summarized in Table 2.

Since 2011, the “Bulletin of the American Meteorological Society” has published an overview of all climate impacts studies for selective extreme weather events of the year before. The evaluation of all published modelling approaches has shown that 65% of the studies concluded that the frequency and intensity of the analysed extreme weather event was influenced by climate change (Munich Re, 2017). Therefore, the analysis verifies the interrelationship of climate change and the frequency and intensity of climate-related extreme events.

Despite the number and intensity of such events and the consequent losses are seemingly increasing, there is still much doubt about the respective human influence as natural climate variability masks the potential for anthropogenic changes in the climate.

Climate is a statistical information that contains the average weather condition of a region for a specified interval usually longer than 30 years (FAO, 2007). In contrast, the weather is a day-to-day state of the atmospheric condition in a given place. It includes short-term variations such as temperature, precipitation or wind, that last hours, days, weeks, or a few months, in contrast to the long-term variations of the climate that last for years and longer (Ruddiman, 2014). Therefore, climate variability can be defined as variations in the mean state of climatic parameters and other climate statistics on all temporal and spatial scales beyond those of individual weather events (FAO, 2007).

Table 2: Major climate-related loss events from the past decades.

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Source: Munich Re (2017).

The general concept of climate change refers to a significant variation in the mean state of the climate or its variability that can result from either natural internal processes within the climate system, or from natural or anthropogenic external forces (McDonald, 2010).

The effect of climate change on extreme weather events can be visualized in relation to their probability of occurrence as shown in Figure 2. The left panel shows a shift of the entire distribution towards a warmer climate. This shift leads to an increase of extremely hot weather and a decrease of extremely cold weather. The right panel illustrates an increase of the temperature variability, with no shift in the mean, a situation that would equally lead to an increase of more extreme cold and hot days. The bottom panel shows an altered shape of the distribution towards the hotter part of the distribution, while the

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Figure 2: The effect of changes in temperature distribution on climate-related extreme events. Different changes of temperature distributions between present and future climate and their effects on extreme values of the distributions: (a) a simple shift of the entire distribution towards a warmer climate; (b) an increase in temperature variability with no shift of the mean; (c) an altered shape of the distribution. Source: IPCC (2012); adapted from Thornton et al. (2014). temperature probability distribution keeps its mean. All of the three panels may be combined to depict how the effect of a changing climate will possibly influence the frequency and intensity of extreme events in the future.

Climate extremes are generally defined by their probability of occurrence, their exceedance of specific thresholds, or both. In the Special Report of the IPCC on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX), an extreme climate or weather event is defined as:

“The occurrence of a value of a weather or climate variable above (or below) a threshold value near the upper (or lower) ends of the range of observed values of the variable” (IPCC, 2012) .

However, there is no ultimate definition, as they all have limitations when it comes to their respective impact for several reasons. First, the impact not only depends on the character of the extreme event but also on the level of exposure and vulnerability of the affected system. Second, not all extreme events must have extreme impacts, i.e. the impact of a weather event must not necessarily be extreme because it exceeds certain thresholds.

Variations in climatic parameters such as temperature have generally been attributed to natural causes in the past, but due to the rapid changes since pre-industrial times, an increasing number are now ascribed to human activities. While the past long-term trends of climate change are considered to be largely caused by humans, this attribution is more complicated when it comes to single extreme weather events, as such events usually result from a combination of multiple factors, and a broad range of extreme weather events could happen even if the climate is not changing (IPCC, 2012).

However, statistical climate models have helped to prove that the probability of the occurrence of such events has increased in the past decades, and much progress has been made in attributing the incidence of extreme weather events to specific causes. As a result, there is strong evidence today linking the increasing number and intensity of weather extremes to the influence of anthropogenic climate change ( IPCC, 2012; Coumou & Rahmstorf, 2012; EEA, 2017).

2.2.3 Global climate change projections

The aim of the 2015 Paris Climate Conference (COP21) was to achieve a legally binding agreement between the nations to keep global warming well below 2°C above preindustrial levels since this would significantly reduce the impacts of climate change (UNFCCC, 2015). However, this seems to be truly ambitious, considering the estimates from the AR5, projecting an increase of the global mean temperature of 1.5 – 4.5°C by the end of this century (IPCC, 2013). In fact, current mitigation plans may lead to an increase of at least 3°C, not even considering the altered political situation in the United States of America, the second-largest emitter of carbon dioxide in the world (UNEP, 2015).

To assess the potential impacts of future climate change on food systems one has to use data that predicts future climate change based on storylines about future development, including driving forces such as demography, economy, technology, land use, or agriculture (IPCC, 2000). These climate change projections are based on two components: a time path of greenhouse gas emissions and a General Circulation Model (GCM), which is a mathematical model, simulating the response of the Earth’s climate system to the increasing greenhouse gas concentrations (IPCC, 2013). Many such scenarios have been developed by the IPCC and are widely used for the analysis of climate change impacts and possible options for mitigation and adaptation. Most of the climate impact studies concentrate on changes in the mean climate, since abundant data is available, and in terms of model output, these changes are more robust (Thornton et al., 2014). However, by only focusing on changes in climate means, the full spectrum of climate change impacts is likely to be underestimated. Climate change projections steadily improve, and nowadays are not only able to demonstrate that global warming will continue for many decades to come, but also bring strong evidence that the frequency and intensity of climate-related extremes as well as climate variability will further increase, posing unknown threats to our globalized food systems (Coumou & Robinson, 2013; IPCC, 2012)

2.3 Direct impacts of climate change on food production

Climate change has various impacts on food systems and it affects all of the four pillars of food security, however, the main emphasis of this chapter lays on the direct impact of climate change on agricultural productivity. More precisely, it gives an overview of the recent trends and the most prominent projections of the long-term effects of climate change, and the observed and projected near-term effects of an increasing climate variability and a growing incidence of extreme events on agricultural production. The impacts are projected to be “complex in nature, geographically and temporally variable, and largely influenced by social and economic factors” (Vermeulen et al., 2012). Accordingly, there is much variation among countries and crops, particularly due to the different trends in yields and climate. Understanding the past trends is essential in estimating the future impacts on agricultural production, and therefore it helps to adapt to the adverse effects of climate change and extreme events. Moreover, identifying key agricultural commodities and countries that have been most affected by recent trends is necessary to analyse the potential indirect impacts of climate change on food systems, reaching beyond the direct impacts of climate change.

The major source of knowledge for this kind of impact studies comes from both historical statistical studies and integrated assessment models. The first category analyses the direct impact of weather anomalies and climatic trends on food production; the latter combines the direct impact from weather on yields, derived from crop models, with downstream impacts on food prices, transportation routes, food safety and/or food quality, all affecting the global food security outcome. Clearly, both climate and crop models comprise significant uncertainties as each model is composed of numerous variables derived from assumptions about the extent and rate of future climate change. Moreover, the weighting of the different variables and the predominant drivers of change, developed from knowledge about physical processes and statistical linkages, often remain controversial (Singh, 2009).

2.3.1 Sensitivity of agricultural production to climate change

The impact of climate change on food production was not heavily emphasized in the fourth IPCC assessment report (AR4). However, the results indicated that, up to 2050, temperate regions would benefit from a mean temperature rise of 1-3°C, in terms of crop yield increases, whereas most of the tropical regions would experience yield decreases, because the climate of many tropical regions is already close to the temperature thresholds of most crops (IPCC, 2007a). Higher mean temperatures, beyond 2050, would make all regions susceptible to yield losses, especially in tropical regions, where the adaptive capacity is projected to be exceeded (ibid.). In contrast, new results from the consequent AR5 suggest that more yield decreases than increases, even in temperate regions with less than 3°C of local warming (IPCC, 2014a). Moreover, AR5 gives great attention to the adverse effects of extreme events that exacerbate the impacts of a gradually warming climate. A variety of yield impact studies document a large negative sensitivity of cropping systems to climate change, climate variability, and various kinds of extreme events, particularly, high temperatures and heavy rainfall, and the associated heat waves, floods and droughts.

There are many factors that influence the metabolism and hence the growth and productivity of a plant. Thus, it is a complicated task to anticipate the influence of a changing climate on the productivity of a specific crop. Important climatic, atmospheric and environmental factors that influence yields, both positively and negatively, include the amount of CO2 in the atmosphere, the temperature, the amount of precipitation, and the natural characteristics of the soil. The relationship between these factors, the plant, and the resulting yield, depend on the geographic location, the crop variety, the management of the soil, and the duration and timing of crop exposure to the prevalent conditions of the weather and climate (Porter et al., 2014).

To bring more clarity and order to the large number of interrelated factors that influence the productivity of crops, and hence the availability of food, a distinction between the long-term impacts of changes in climatic means on the one hand, and the short-term effects of increases in climate variability and in the frequency and magnitude of extreme events, on the other hand, must be made. Both long-term effects and short-term shocks impact on production as well as postproduction activities. Yet, in the short-term, growing climate variability and especially the occurrence of extreme events have more immediate effects on food system activities than long-term changes in means (Vermeulen et al., 2012). However, the risk to food production from changes in mean climatic values, such as rising temperatures, is growing over time.

2.3.2 Long-term effects of climate change

Temperature is one of the most important factors in determining the productivity of crops. Model results from the past have shown that various physiological processes of plant growth and development, ranging from reduced grain set (Moriondo et al., 2011), shortening of the time to plant maturity (Iqbal & Arif, 2010), increased plant sterility and plant mortality events (Sánchez et al., 2014) are, among others, all affected by temperature. Yet, the response to temperature depends very much on the availability of water. Generally, there is a negative correlation between water stress and high temperatures.

The analysis of 66 yield impact studies for major crops has shown that yields of wheat and maize drop with temperature increases of 1°C to 2°C of warming in low latitudes, and with 3°C to 5°C in high latitudes (Porter et al., 2014). Yet, the relationship between yields and temperature is nonlinear. For example, Schlenker & Roberts (2009) found the yields of wheat and soybean in the United States to be gradually increasing up to a temperature of 29° to 30°C; above these thresholds, yields rapidly decline. Accordingly, area-weighted average yields of this two crops would decrease by 30-46% under the slow-warming scenario B1, and by 63-82% under the fast-warming scenario A1FI, until the end of this century (Schlenker & Roberts, 2009).

Despite the great uncertainties in predicting global-scale yields for any time frame, Funk & Brown (2009) used a set of GCMs to predict that global per capita cereal production declined by 14% between 2008 and 2030, assuming that per capita harvested area would continue to grow faster than yields. Moreover, Nelson et al. (2009) used two GCMs to estimate yield changes for maize, wheat, and rice in developing countries between -27% to +9%, and -9% to +23% in developed countries until 2050, assuming a positive fertilization effect of elevated CO2.

The positive fertilization effect of CO2 is another key issue when estimating the impact of climate change on agriculture. However, the magnitude of its positive effect is much debated and not only depends on the soil and the prevalent availability of water and nutrients, but also on the temperature, and in particular, on the crop species (Porter et al., 2014). Observational evidence shows that the positive effect of higher CO2 concentrations is larger in C3 plants (e.g. wheat, rice and soybeans) than in C4 plants (e.g. maize) because C4 plants are less responsive to increased CO2 (Leakey, 2009). However, Singh (2009) argues that elevated CO2 concentrations affect the nitrogen balance due to changes in the physical plant structures and, as result, reduces the tolerance to drought. Moreover, increased carbon assimilation rates are only beneficial for the plant growth if sufficient nutrients are available (Müller et al., 2009). Conversely, theory suggests that water-stressed crops will benefit more from increased CO2 than well-watered crops because field experiments have shown that rising CO2 concentrations increase the efficiency of agricultural water use, and thus, are expected to reduce crop water use by 4–17% by 2080 (Deryng et al., 2016). Furthermore, a meta-analysis by Taub, Miller, & Allen (2008) stated that elevated CO2 (540–958 ppm) would indeed have a positive effect on plant growth, but reduces the protein concentration of wheat, barley, and rice by 10–15% and of soy by 1.4%. In summary, one can expect a beneficial effect of elevated CO2 on specific crops, but the prevalent conditions must be well observed and the possible counter effects on food quality and resistance to extreme weather conditions must be taken into account.

Müller et al. (2009) studied the global effect of climate change on agricultural productivity of 11 major crops (wheat, rice, maize, millet, field pea, sugar beet, sweet potato, soybean, groundnut, sunflower, and rapeseed) between 2000 and 2050. The projected changes in yields were generated from three emission scenarios across five GCMs to compare the two 10-year periods: 1996–2005 and 2046 to 2055, neglecting possible future changes in agricultural practices or crop varieties, and the effect of elevated atmospheric CO2 concentrations on these crops (Müller et al., 2009). The results, shown in Figure 3, suggest that climate change will depress agricultural yields in the majority of all countries. However, large geographic disparities exist between the projected outcome on yields. The map demonstrates the great difference between the northern hemisphere that is in great parts projected to benefit from climate change, and the southern hemisphere, where the opposite seems to become true. Even though there are still uncertainties in estimating the impact of climate change on yields, and specific projections differ according to the climate scenario or simulation method used, the broad-scale spatial pattern on crop productivity has remained consistent across all global-scale studies of the past decades (Wheeler & von Braun, 2013).

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Figure 3: Global impacts of climate change on crop productivity by 2050. The figure shows the estimated percentage change in 11 major crops from 2046–2055, compared with 1996–2005. Simulated changes in yields are averaged across three emission scenarios and five GCMs, assuming no positive CO2 fertilization effect. Areas where no robust data was available are grey. Source: Müller et al. (2009); adapted from World Bank (2010).

The results suggest that by 2050, there might be a shift of production zones from south towards north and, thereof, a redistribution of agricultural potential following the spatial pattern of the impacts of climate change. Therefore, many countries in the global south are expected to be hit the most by climate change while at the same time these countries will experience the greatest increase in population. As a consequence, many areas that are highly dependent on agriculture will be confronted by a decreased self-sufficiency in food production and, hence, in the availability of food (Müller et al., 2009).

To reveal the disparity of yield impacts at the national scale for major producing regions and for individual crops, Lobell, Schlenker, & Costa-Roberts (2011) estimated the response of average yields for four major crops to global temperature and precipitation trends for the 29-year time period of 1980 to 2008. Publicly available datasets on crop production, crop locations, growing seasons, and monthly temperature and precipitation were combined to measure the impact of historical weather on crop yields for maize, rice, wheat, and soybean. Large differences were detected between the individual crop producers, revealing winners and losers at the country-scale. Countries, most affected by past climate trends are Brazil for maize, Indonesia for rice, Russia for wheat, and Paraguay for soybean. The estimated net impacts of climate trends on crop yields for the major global producers are shown in Figure 4. At the global scale, the combined impact of temperature and precipitation trends on these four crops ranged from -0.1% for rice to -5.5% for wheat, shown in Table 3.

Table 3: Median estimates of global temperature and precipitation trends (1980–2008) on average yields for maize, rice, wheat, and soybean.

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Source: adapted from Lobell, Schlenker, & Costa-Roberts (2011).

The results indicate a significant sensitivity of crop yields to changes in temperature and precipitation. In particular, changes in temperature seem to be more important for average crop yields than changes in precipitation. Since the magnitude of the fertilizing effect of CO2 is uncertain, it has been excluded from the original table shown in Lobell, Schlenker, & Costa-Roberts (2011). Nevertheless, even though the positive effect of CO2 has been excluded, so has the impact of extreme temperature and precipitation events. Therefore, the results presented here still might be too optimistic and must be viewed with caution.

2.3.3 Short-term effects of climate variability and extreme events

In contrast to the large number of quantification attempts of the impacts of climate change on crop yields, impact studies on changes in climate variability and the effects of extreme events are limited.

In terms of model output, changes in mean climate are more robust than changes in variability, and extreme events occur too rarely to be sufficiently calibrated and tested (Thornton et al., 2014). Despite the difficulty of modelling the impacts of extreme events and climate variability, they clearly have large impacts on various food system activities, reaching beyond the impacts of changes in climatic means and must be taken into account. Besides, the impacts of extreme events can be easily distinguished from the impacts of a changing climate as the effects become apparent directly after the event, posing an immediate threat to the global food production.

As discussed before, it is commonly anticipated that climate and weather variability will increase, whilst the global climate is changing (Figure 2). In fact, climate variability already today has large impacts on many cropping systems since the plant growth and development is particularly sensitive to variations in rainfall and temperature. However, the role of water availability and temperature very much depends on the region, thus, strengthening the role of rainfall and temperature variability in already warm, water prone areas. Furthermore, Craine et al. (2012) concluded that the timing of climate variability might be as important as its magnitude since key physiological processes in the development of the plant are particularly sensitive to the timing of climate variability.

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