ReviewParadigms of climate change impacts on some major food sources of the world: A review on current knowledge and future prospects
Introduction
Climate variability has been and continues to be, the principal source of fluctuations in global food production in developing countries (Oseni and Masarirambi, 2011). The Earth’s climate has warmed by approximately 0.6 °C over the past 100 years with two main periods of warming, between 1910 and 1945 and from 1976 onwards and is greater than any other time during the last 1000 years (IPCC, 2014). Undoubtedly, agricultural production is going to be affected due to its consequences and the magnitude of which on crop yields will vary locally due to regional differences in both natural and anthropogenic factors that control plant responses (Rustad, 2008, Wei et al., 2014). Coupled with resource scarcity of land, water, energy, and nutrients, declining soil quality, increased greenhouse gas emissions and surface water eutrophication, climate change will affect crop production in a great deal (Fan et al., 2011, Tripathi et al., 2014). Changing temporal and spatial trends of hydro-climatic variables, rising sea levels and increasing incidence of extreme events pose new risks to future food insecurity in all parts of the globe (Chen et al., 2015, Zhao et al., 2015). Anomalies in temperature and climatic regime of our earth system have raised the concerns to think global climate change as a strongest stressor for the agriculture and world food production since plants are directly related and respond to environment CO2 and temperature (Kersebaum and Nendel, 2014). Therefore, the potential impacts of climate change on food security must therefore be viewed within the larger framework of changing earth system dynamics and multiple socio-economic and environmental variables.
Various critical direct and indirect consequences of global climate change on crop production can be seen due to the rising CO2 and temperature and unpredictable rainfall disturbing the food security aspects of the world (Poudel and Kotani, 2013). Consequently it becomes quite important to examine the changes happening at different stages of the crop growth and development and their impact on the production either in the form of quality or quantity. As this subject has gained enormous importance in recent times with growing numbers of specific studies of the impacts of climate change on various food items; multidisciplinary synthesis of the knowledge of climate impacts on major food sources of the world is needed.
The ‘climate’ may be referred as the characteristic weather conditions (viz. air temperature, precipitations, atmospheric pressure, humidity, wind, sunshine and cloud cover) of the earth’s lower surface atmosphere at a specific location. Any change compared to prior observations in an existing observation record of the systematic measurements of these phenomena at a specific location over several years may be ascertained as climate change. However, an internationally agreed definition of the term “climate change” is still desirable which on different international platforms is regarded as (i) only human-induced changes in the climate system (UNFCCC, 2006), or (ii) all changes in the climate system, including the drivers of change, the changes themselves and their effects (GCOS, 2012); or (iii) long-term changes in average weather conditions (WMO).
The world is now frequently experiencing many unprecedented changes in climate due to warming of the earth's system since last five decades. The assessment report of IPCC (2014, AR-V) identifies the changes as well as gives various projections in current climatic variables. Each of the last three decades has been successively warmer than any preceding decade since 1850 imparting warmest 30-year period (1983–2012) in the Northern Hemisphere, in last 1400 years (IPCC, 2014). The atmospheric concentration of CO2 has increased to the level of 396.48 μmol mol−1 in 2013 (ESRL-NOAA data, Fig. 1A) from its pre-industrial level of 280 ppm and is projected to reach 550 ppm by the middle of this century which may escalate up to 700 μmol mol−1 by the end of this century (Raupach et al., 2007). Evidently, the Earth’s system shows a warming of 0.85 °C, over the period 1880–2012 and the ocean warming is also increasing on a global scale and is largest near the surface; and the upper 75 m warmed by 0.11 °C per decade over the period 1971–2010 (IPCC, 2014). Further increase in GHGs will have a significant impact on global climate since in unmodified conditions of current energy uses; mean annual global surface air temperature will be raised by 1.5–4 °C (Wheeler and von Braun, 2013). This will have far reaching consequences on each type of ecosystems of the world including agro-ecosystems hence is dangerous for the food security of growing world’s population.
Despite of the huge importance of the industrial production in the world, agriculture has an essential role in ensuring the food security and welfare of growing population (Rustad, 2008). Climate change associated impact on global food security is a threat with which the world will have to deal in the twenty-first century (Myers et al., 2014). Climate change will probably have direct impact on tropical and temperate regions where high temperature or inadequate rain often limits crop productivity (Wheeler and von Braun, 2013). Changed weather conditions will have serious impacts on food availability, accessibility, utilization and food system stability (Gu et al., 2010) and thus food security will be affected. As the growth and development of any plant depends on various environmental factors and their interaction (such as temperature, precipitation, moisture and pressure, etc.) (Cutforth et al., 2007); a plant will behave differently in different interactions and will show different impacts. The impacts will be either visual or changes will happen in its physiology and at the level of other biological processes (Cicchino et al., 2013). The quantitative and qualitative estimates of climate change impacts on crop yields are derived from various crop simulation models for almost all continents (Parry et al., 2004, Krishnan et al., 2007; Table 1). These simulations include higher temperatures, changes in precipitation and higher atmospheric CO2 concentrations to make advance assessment of climate effects across a range of crops (Reidsma et al., 2010). However, some studies show that in current climatic scenario the increasing levels of the CO2 may give some positive impacts on the crop production due to higher net photosynthetic rates and reduced transpiration but at the same time increase in the temperature negates this and different crops show variable impacts (Gu et al., 2010, Mishra et al., 2013; Table 1). On the other hand, increases in the level, timing and variability of precipitation may benefit semi-arid and other water-short areas by increasing soil moisture, but can aggravate problems in water excess regions (Schlenker and Lobell, 2010). Meanwhile a reduction in rainfall could have the opposite effect as well (Braun and Markus, 2012). Various specific crop and climate scenarios for the selected food sources in this assessment have been given here to understand the projected specific impacts of the changing climate on the particular food sources on different continents (Table 1).
Based on recent literatures and published data, this synthesis seeks to elucidate the potential impacts on different bio-physical processes of some important food sources of the world to understand the impact scales and their dimensions affecting the yield over the globe. Our primary goal here is to review observations of climate change impacts occurring on major food sources across the world and to find out evidences on crop responses to different kinds of stress produced due to changes in climatic factors. This deals with the various dimensions of climate change impacts on some major food grains (wheat, rice and maize), examines and points out the major changes happening at different level of vegetable and fruit crops and integrates the various findings of published researches on the impact of climate change on fish-food which is also one of the major sectors fulfilling food demand across the world. It also tries to find out the winter and summer sensitivity differences in selected food sources, ways of stress responses and acclimation patterns to fight with the climate change induced stresses. Major climate change adaptive and mitigative strategies to cope up with the impacts have also been illustrated in brief.
Section snippets
Impacts on major food grains
The wheat, rice, and maize are among the six most widely grown crops in the world (Lobell et al., 2011). Production of these crops accounts for over 40% of global cropland area, 55% of non-meat calories and over 70% of animal feed (FAO, 2008). Historical climate and crop data have been used to indicate climatic impacts on yields of these grains in many countries of the world (Schlenker and Lobell, 2010). In the following sections three major crops of the world and their responses under the
Climate change induced stress responses
Temperature stress produces detrimental effects on plant and animal metabolism through disordered cellular homeostasis, and extricated physiology in plants (Seiler et al., 2011). Largely the induction of heat-shock protein (HSP) synthesis induces thermo-tolerance (Suzuki and Mittler, 2006). Stress-induced cellular changes bring enhanced buildup of toxic compounds such as reactive oxygen species (ROS; e.g. superoxide; (O2–) produced by NADPH oxidases, 1O2, H2O2, and HO) which are toxic molecules
Summer and winter sensitivities of the crops and their acclimation patters
Sensitivity of the crops towards short term climatic changes is an important parameter to be taken into account while dealing with the impact studies of climate change (Mondal et al., 2014). Any sudden change in normal growing temperatures in summer and winter growing crops may induce many bio-physical alterations (Table 3). Sudden high increase in temperature in summer crops and chilling, freezing and warm conditions during growth of winter crops affect growth and development by upsetting
Combating climate change impacts: agricultural adaptation and mitigation strategies
There are varied risks of climate change and thus there is a strong need for successful adaptation and mitigation strategies across different scales and dimensions of impacts depending upon crops and region (Table 4). The important risks of increasing warming of globe are variable and untimely rainfall events, unstable winter seasons, more disease occurrences and crop failures (Adger et al., 2005). However, many research outputs indicate that prolonged short growth season collectively with
Conclusion and future approaches
To summarize, it can be stated that world’s food security is in immense pressure under climate change and much complex to understand due to interactions involved at every stages of the life cycle of a food source. Climate change; is unswervingly influencing the human survival through its agricultural impacts by higher temperatures, droughts, shifts in cropping areas, floods, soil erosion, and rainfall variations affecting the food security of the globe. Reduced quality and quantity of major
Acknowledgements
Authors would like to thank The National Academy of Sciences (NASI), Allahabad, India for their financial support in the form of fellowship and The Institute of Applied Sciences, Allahabad, India for its institutional support. Dr. Durgesh Kumar Tripathi is acknowledged to the University Grants Commission (UGC), New Delhi, India for providing Dr. D.S. Kothari Post Doctoral Fellowship.
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