Crops and Ecosystem Services, a Close Interlinkage at the Interface of Adaptation and Mitigation

Abstract

Beyond the occurrence of extreme events, heat waves and increasing climate, interseasonal instability is expected to affect more frequently field crops and more broadly ecosystems. Ecosystem services will be at the core of adaptation to a steadily evolving situation. The role of biodiversity is crucial in this regard building the resilience of crops and ecosystems. Understanding how the changing climate, in different parts of the world, will affect plants according to their eco-physiological limits is challenging. Ecosystem services planned at a territorial level are part of the answer, mitigating local climate, regulating hydrological cycles, allowing soft pest control, and contributing to carbon sequestration. Technical solutions are part of the equation, but the potential of genetic optimization should not be overestimated, against the limits of the existing genetic diversity.

1. Introduction

Extreme climatic events, such as storms, hail, droughts, or megafires, mark the spirits and are the most visible events related to the effect of climate change. They mark the spirits and are as such highlighted in media, as well as in the Intergovernmental Panel on Climate Change (IPCC) report [1] and are subject to political communication. However, the longer-term progressive impact on ecosystems, which will in turn as well affect agricultural production systems, is more complicated to apprehend. Beyond the occurrence of extreme events, increasing climate interseasonal instability is expected to affect more frequently field crops and more broadly ecosystems.

It is indeed more complicated and more uncertain to communicate upon impacts that are more pernicious not only due to slow and continuous deterioration but also based on predictive models whose temporality cannot be precisely predicted. Risk analysis remains mainly based on past meteorological data analysis and often on metadata like average or mean temperature. Yet, as an increase in greenhouse gas emissions on a global scale continues year after year, the world is entering a period of chronic climate instability unparalleled on the scale of human history.

Several structural phenomena will thus combine and affect agricultural production systems both locally and on a global scale. This will result in a structural progressive deterioration of food production and ecosystems over time.

Climate change is often reduced to a change from an initial situation to a new one, to which we need to prepare ourselves to adapt. However, the idea that there will be no new stable situation as such, but instead a permanent instability and change over time, is destabilizing and not well understood in most cases. The idea that climate change would induce benefits to colder regions of the world and thus also mainly affect warmer ones is as well widespread and can be reassuring [1]. This is reflected in the IPCC report [1], as well as in the Notre Dame Global Adaptation Index [2], suggesting between lines that developed countries have the means to face the consequences of climate change while the main issue is about supporting vulnerable ecosystems and poor populations. The concept of vulnerability is correct, but the idea that some parts of the world would not be affected or would have sufficient means to cope with any generated situation is misleading. Looking more closely at the impact on ecosystems, agricultural production and food security may provide useful insight to get a better understanding of upcoming challenges.

2. Past and present global change: What can be learned from earth history?

The accumulation of Green House Gas (GHG) in the atmosphere is the main factor triggering the global warming phenomenon. However, other factors are involved in reinforcing or mitigating the warming or cooling effects over time.

The Green House effect has been crucial in the earth’s history allowing the atmosphere to be warm enough, while the Sun activity was much weaker than it is nowadays. Over time, huge quantities of carbon have been stored in the soil during different geological periods. Earth’s global temperature has been varying over geological times according to the atmosphere’s composition, the land cover evolution, the earth’s circumvolution around the sun, and the long-term sun radiative intensity, among other factors [3].

2.1 The Permian mass extinction

At the end of the Permian era about 252 million years ago, massive eruptions to the North East of the Pangea, in an area now located between the arctic circle and Central Asia, released massive quantities of GHG resulting in a steep increase in air temperature. Research on fossils in geological layers shows that approximately 95% of living species disappeared by that time.

Besides rising temperatures affecting terrestrial life, the main factors triggering the mass extinction of marine life have been analyzed as declining oxygen levels in the water, rising water temperatures, and most likely also ocean acidification [4, 5]. Those factors are similar to trends observed nowadays.

Geological probes show that algae bloom occurred [6]. Those events are favored by carbon dioxide (CO2) concentration in the atmosphere, high temperatures, and abundant nutrients. The decomposition of the algae consumes the oxygen, leaving other living organisms to die. Such events can be observed nowadays in rivers, lakes, and tropical sea hot spots like the Gulf of Aden. Another parallel with the ongoing global warming is the increase in the frequency of wildfires [6, 7].

Very important sedimentary layers witness the erosion that prevailed during this period [7]. The assumption is that the loss in land cover, which resulted from the disruption of the ecosystem jointly with heavy rain episodes, resulted in an erosion process rarely observed in Earth’s history.

2.2 The quaternary glaciation cycles and the Holocene period

Over the quaternary, the Pleistocene period beginning 2.6 million years ago included more than 50 large-scale climatic oscillations between cold periods persisting for as much as 100,000 years and interglacial periods of about 10,000 years [8]. The Holocene, beginning about 12,000 years ago, is the most recent period of the Quaternary era characterized by the development of human settlements. At the end of the Pleistocene, 20,000 years ago, most of the Northern European and American continents were covered by glaciers. With the ensuing warming period, the sea level has risen by about 120 m [9]. The temperature increase over the period is estimated at 1.5°C by four different models and about 5°C by one model. According to all five models, most of the warming occurred between 12,000 and 10,000 years ago and reached a maximum around 6500 years ago. A cooling period with a global average loss of 0.5°C ensued until the industrial era. The trend reversed again at the end of the nineteenth century, with a steep temperature increase of 1°C on average.

2.3 Global warming and ongoing challenges

Even though, the warming pace over 2000 years has been quick, the ongoing global warming is much faster and is evolving toward a higher temperature increase than the warming that happened since the last glaciation period. From this perspective, the consequences of the ongoing global warming might rather be compared to the event at the end of the Permian era.

The human action impoverishing and reducing natural ecosystems and the scope for the services they can provide is a cofactor that creates negative synergies with global warming.

The faced changes are expected to be progressive, at the scale of human life, even though at an increased speed over time and in any case at a too-fast pace to allow ecosystems and living beings to adapt. The consequence will be the extinction of species intervening in different regulation cycles and as a consequence, the impoverishment and loss in the resilience of ecosystems.

Besides, other factors influence the local climate adding to global warming, reducing ecosystems and human settlements’ resilience, in turn reducing the carbon storage capacity and contributing to the release of additional GHG.

The relationship between ecosystems, land cover, climatic extreme events, and erosion is at stake with detrimental consequences for life on earth and for humanity.

The fact that in a temperate environment, as is the case in part of Europe, there is a greater margin for adaptation in the short or medium term than in other warmer regions of the world, does not mean that the ambient conditions will not deteriorate in a similar manner, in the longer term. Thus, in addition to the risk of frost in winter, heat waves are likely to become an increasing matter of concern. Climate instability is also likely to increasingly affect ecosystems and food production.

Meteorological prospective models take into account the occurrence of high temperatures [10]. However, downscaling models, at the local level, taking into account the interrelations of global and local factors remain insufficient. This is especially true for open-field agriculture.

3. Factors affecting the climate at the local level

3.1 Geophysical and environmental factors

Local climate conditions are influenced by other factors that differentiate them from each other. The latitude, the proximity of a coast or continental position, oceanic currents, and winds influence meteorology; the same applies to land cover and urban extension.

Climate change is likely to affect drastically already warmer areas in the short term, while temperate regions are likely to face more climatic instability in interseason periods and face more progressively high-temperature limits.

From an agricultural perspective, the limiting factors, at a given point in time, are not the same in different parts of the world.

Between Ecuador and the South and North Tropics, the high soil exposure to Ultraviolet (UV), the high temperatures, and strong rains are important factors distinguishing the local conditions from those that prevail in temperate regions. Under tropical latitudes, soil’s organic layer is quickly degraded as soon as it is in direct exposure to the sun, limiting the scope for carbon sequestration and fertility conservation. High temperatures limit plant growth in the absence of permanent land cover.

In temperate regions, cold remains a limiting factor especially under high latitudes, while snow cover increases the soil albedo in winter and releases water over a longer period in spring into summer.

Besides, the local climate is influenced by ocean currents warming the climate in Northern Europe and cooling it in North America and South Africa’s Atlantic coasts, while continental areas are more prone to cold winters and hot summers. Land cover also plays a crucial role in mitigating climate and regulating rainfall [11]. In continental areas, rain forests play a similar role to oceans regulating climate. Those influences will remain, but large-scale modifications in land cover result in climate changes at the local and regional level, unrelated to the global warming phenomenon, while in many cases worsening its effect. Urban sprawl and deforestation are both affecting local climate conditions.

3.2 Urban sprawl

Urbanization increases the warming effect locally by increasing infrared irradiation toward the atmosphere, thus increasing the warming effect at the local level. Urban areas expand often replacing agricultural earth and forests reducing at the same time the carbon sequestration potential.

Besides the loss of food provisioning potential, the soil absorption is modified so that flood risk is increased and groundwater inflow is decreased. The local climate is also modified influencing temperature and rain parameters including over the surrounding countryside.

Where urbanization happens on rangelands, like arid or semiarid areas, the triggered change can be marginal. The impact on the local climate and hydrological cycle can also considerably vary according to the latitude and environment.

However, the overall urbanization of increasing surfaces at a quick pace is a worsening factor in the background of global warming, which should not be underestimated from a climate and food security perspective.

By 2100, the urban land could range from about 1.1 million to about 3.6 million km² (roughly 1.8–5.9 times the global total urban area of about 0.6 million km² in 2000). Under a middle-of-the-road scenario, new urban land development amounts to more than 1.6 million km² globally, an area 4.5 times the size of Germany. Global per capita urban land is expected to more than double from 100 m² in 2000 to 246 m² in 2100 [12].

Urban growth is triggered by the increase of population worldwide as well as by the trend of populations searching for a greener environment. Since the mid-1950s, European cities have expanded on average by 78% for a population growth of 33% [13].

Beyond the impact on local climate and hydrological cycles of soil artificialization, permanent land cover over large areas, especially in the vicinity of urban areas, is of utmost importance in mitigating local climate.

3.3 Land cover and role of forests

At the local level, temperature is influenced by the land cover albedo and evapotranspiration. The albedo varies according to soil wetness, color, structure, and type. Sand reemits less infrared than some stones or rocks, while a dense tree cover offers a stronger cooling effect through evapotranspiration, varying according to the latitude and related local meteorological conditions.

The results of a study carried out in the North-East of China [11] show that forest cover regulates the local climate allowing slightly warmer temperatures in winter and lower in summer. An almost negligible average temperature increase of 0.04 +/− 0.02 Celsius degrees over the year is reported. Besides, there is a yearly increase in rainfall of 17.49 +/− 3.88 mm, which is predominantly increasing (93.8% of the yearly increase) in spring and summer when it is the most useful for agriculture.

The forest cover has a stronger cooling effect under higher temperatures. The role played by forests across Europe and the United States is thus expected to increase with global warming. The plants’ evapotranspiration capacity is measured according to the Leaf Area Index (LAI). The higher LAI and evapotranspiration, the higher the potential cooling effect. Forests have a warming effect at night and in the winter period. In Europe, the forest cover climate mitigation is stronger from North to South and from West to East where continental conditions prevail [14]. Under high latitudes, forests play an important role in mitigating cold events in spring.

In tropical forests, the highest trees forming the canopy regulate the climate for lower layers of vegetation. Trees have different capacities to cope with air temperatures (Ta). This is used in models measuring the difference between mean canopy leaf (Tc) to air temperature (Tc–Ta) [15]. The higher the difference, the more resilient is the tree. More resilient trees present smaller leaves and larger stomatal conductance. Pometia tomentosa presents a high leaf temperature tolerance, which can reach 31.8°C, while Mezzettipsis creaghii records a maximal measured leaf temperature that can reach 21.6°C [15]. The difference of 10°C between the canopy and lower forest layers is characteristic of tropical forest microclimate. At the canopy level, photosynthesis is active until 2 p.m. when temperatures reach the day’s height and then reduce drastically. The soil moisture has a strong influence on the plant’s surface temperature and the capacity to sustain high air temperatures. However, beyond a threshold that varies according to plants, biomass productivity drops drastically and can endanger the plants’ survival capacity. The forest density and intermediary layers are also of utmost importance to protect the soil from desiccation, preserving the soil moisture. Tree species diversity also contributes to increasing the forest’s resilience to high temperatures.

The extent of deforestation, including the size of forest patches and spatial distribution, changes the impact of orest regression. In Latin America and in the Congo Basin, deforestation is increasing. In South America, 919,000 km² has been lost between 2000 and 2013 [16]. Carbon sequestration is affected by forest regression with a global effect expected in the medium- and long term, but the local impact on regulating services is affecting more directly local populations.

Where the permanent vegetation cover regresses, the climate is modified at the local level [17]. Soil heating increases air temperature and contributes to reducing rainy periods [18, 19], which are concentrated in more violent events, while the soil loses its ability to retain water.

Whether under tropical or temperate climatic conditions, spatial forest fragmentation threatens their resilience and provided ecosystem services. In Amazonia, a shift from large- to small-scale deforestation is taking place, while new hot spots open in Peru and Bolivia and deforestation has accelerated in Colombia [20]. Fragmentation threatens forest resilience and provided ecosystem services. The main drivers of forest fragmentation are wildfires, agriculture and herding pressure, timber logging, and urban sprawl. At the forest edges, conditions related to wind, sunlight exposure, temperature, and humidity are modified [20].

Besides, fragmentation endangers biodiversity, as different species communities are not being able to remain in contact and lose internal biodiversity generation after generation when becoming too small. In this regard, the focus on sole species on the red list of protected species is misleading as ecosystem services broadly depend on smaller barely visible fungi, insects, and bacteria. However, large enough preserved core areas and aggregation of patches in small distances help reduce the negative impact of forest cover regression [20].

Thus, land cover and land cover modification are key cofactors considering the effect of global warming on the local climate. Agriculture is especially sensitive to extreme climatic conditions and climatic instability.

4. Impact of changing climate conditions on ecosystems and crops

4.1 Field crops’ physiological limits

Beyond extreme climatic events, more subtle changes concern, in particular, the disruption of ecosystems and of agricultural production systems due to increasing climatic instability, prolonged episodes of high temperatures beyond the tolerance threshold of plants [21, 22], and the occurrence of events affecting the plants’ physiology at critical times in crop development [23].

In particular, the so-called tropical nights during which the temperatures no longer drop below 20°C disrupting the nocturnal respiration mechanisms necessary for plants [24] are likely to become more frequent. While the frequency of day heat waves and tropical nights will increase the probability that those changes will happen at a critical stage of crop development. Therefore, crop losses are likely to happen more frequently.

The predominant idea is that plants grow best with water, sufficient nutrients, and warmth. This assessment is a little simplistic but nevertheless takes on a form of reality in the relatively stable climatic framework that has prevailed over the last millennia while agriculture has developed. The cold has been one of the main constraints faced by field crops in temperate latitudes in northern Europe and the United States. However, the rapid change over a comparatively short timescale calls into question what seemed acquired.

At a different pace, in different areas of the world, raising temperatures for prolonged periods, beyond the plants’ maximum tolerance, are likely to gradually erode yields [25]. Beyond a maximum temperature, the yield of the plant begins to drop, due to the so-called “zero” production threshold.

The Day Degrees (DD) methodology has been developed to attribute a plant’s growth potential according to the difference between the minimum temperature required by the plant development and the meteorological maximum temperature at day [26]. The Day Degrees concept has been adapted to take as well into account limits in plant growth due to high temperatures [25].

In the West of Uzbekistan (Central Asia), the Day Degree (DD) presents a progressive yield erosion of the main field crops (Figure 1). The Day Degrees concept is applied, taking into account the crops’ high temperatures’ maximal tolerance [25].

Figure 1.

Trend in the day degrees (DD) production potential for the cropping season of winter wheat, cotton, and rice in the vicinity of Khiva (West Uzbekistan), over 1986–1990 and 2013–2017 periods [25].

Besides, the yield erosion in regions where high temperatures affect increasingly crops’ development and extreme events at the time of critical stages of plant development can additionally lead to a drop in production or even a total loss of harvest. The more the climate becomes erratic in interseasonal periods, the higher the probability of the occurrence of such events.

High temperatures have an impact at different stages of a plant’s development. For instance, high temperatures of 38°C during the daytime and 28°C at night cause the following changes in sorghum [27]:

• reduced germination;

• reduced panicle development (flower);

• decreased pollen starch content and potential fertility;

• reduced crop yield (seeds per panicle and seed weight);

• reduced seed fertility potential; and

• reduced leaf development.

Sorghum leaf extension development reaches a maximum level from 32 to 35°C and decreases drastically at temperatures of 37–40°C and above [27]. Some plant development stages are more sensitive to temperature than others. In sorghum, the 10 days prior to flowering (panicle development) are especially critical; high temperatures at this stage reduce pollen viability and thereafter the potential yield.

The second sensitive stage takes place during flowering and the 10 subsequent days. At this stage, high temperatures also result in lower pollination and decreased production of viable grains.

Night temperatures above 20°C, called tropical nights, also affect the plants’ respiration disrupting physiological mechanisms complementary to the day photosynthesis.

Each drop in production over the growing period is an episode where temperatures raise, reaching the zero-production threshold over a week period. In the present case (Figure 2), those episodes did not happen at crop-critical development stages, allowing a good harvest for the region [25].

Figure 2.

Day degrees (DD/DD’) cotton production potential per week over the year 2017 following Khiva (west of Uzbekistan) meteorological data [25].

However, high temperatures at critical stages of crop development are likely to become an increasing risk jeopardizing the expected yields. This risk is expected to increase over time while increasing temperatures will also limit the plant’s vegetative development, as well as reducing yields.

The analysis of data from the World Bank open portal on climate change, for the period until the end of the twenty-first century for Uzbekistan, shows a similar trend in increasing temperatures (Figure 3) observed as the tendency observed in the West of Uzbekistan for the period 1986–2017 [25].

Figure 3.

Trend in the number of hot day events over the twenty-first century on average in Uzbekistan, according to the representative concentration pathway (RCP) 8.5 scenario (World Bank open portal data) [25].

The risk of high temperatures happening at plants’ development critical stages is expected to increase over the next decades, even though at a different pace according to regions of the world while increasing temperatures will also progressively limit the plants’ vegetative development.

Regardless of the frequency of occurrence of temperatures that exceed the physiological limits of plants at critical development stages [22], increasing instability of air masses [28, 29, 30] could further endanger field crops. Intermediary seasons whether spring or autumn are expected to become more unstable with varying temperatures destabilizing crops as well as ecosystems.

4.2 Overall impact of climate change on food production systems

Ecuadorian Africa with particularly fragile tropical ecosystems and agriculture runs a major risk related to high-temperature episodes’ occurrence.

However, it would also be misleading to believe that Northern countries will be spared from food security issues [1]. Food sovereignty in Europe is eroded by urban sprawl [13] and gradually by climatic events that affect production more frequently than in the past; even though, the physiological limits of field crops are yet still rarely reached. The vision that solutions are only a matter of investment, while climate change would not be a direct threat to the richer countries and to the privileged population among those, is misleading.

Besides, while temperatures are increasing, the water demand for irrigation will also increase. The increase in water demand by 2050 in Uzbekistan is expected to increase between 9 and 14% for cotton and between −1 and 5% for winter wheat [31]. At the same time, the inflow into the downstream area is expected to decrease by 26–35% by 2050. The situation will further deteriorate over the second half of the twenty-first century, while the water demand will grow and the Amu Darya River discharge will get radically reduced.

However, drawing a global picture regarding the world food production perspective over time would require a dedicated in-depth analysis.

For the time being, assessments of the impact of climate change on field crops developed among temperate climate countries still rely on the paradigm that droughts are the main risk while high temperatures are rather beneficial as long as enough water is available.

More complex impact assessment models involving high- and low-temperature availability, as well as soil and air humidity parameters are barely available. The interrelation between different parameters including land cover and ecosystems’ resilience might as well require more attention.

The European meteorological data basis, Copernicus [32], provides only metadata, with weekly average temperatures being the smallest presented time unit. The data thus provided do not allow to develop models assessing climate impact on ecosystems and crops. More fine data can be retrieved from meteorological stations, but often require to be purchased.

Land cover will be of increasing importance mitigating the climate for the purpose of food production across the world. Under changing climatic conditions triggered by global warming, this implies resilient ecosystems.

4.3 Role of ecosystems and resilience

4.3.1 Ecosystems and ecosystem services

An ecosystem should be understood as a complex system, which is more than the sum of the species that compose it. The multiple interactions allow positive and negative feedback loops that provide some degree of flexibility to adapt to changing conditions. Parallel mechanisms allow the system to continue to autoregulate itself when a species makes default. It should be understood as a self-sufficient complex system achieving a dynamic equilibrium.

Following the same logic, ecosystem services or nature-based solutions are defined in broad terms, including benefits which, in practice, can be contradictory. This applies, in particular, to provisioning, whether it is about wood logging, crops, or herding, as the ecosystem equilibrium is deeply destabilized as soon as resource production and collection is intensified. Agricultural systems are based on a strongly reduced biodiversity which limits autoregulation mechanisms and thus resilience, even in the case of bioproduction which is more respectful of nature.

Ecosystems as defined herein play a crucial role in providing various services to humankind. They contribute to mitigating local climate, increasing soil water absorption, allowing more and longer water availability for plants, while contributing to refilling groundwater, reducing flood risk, and allowing regulation between species populations, including pests presenting risks for crops.

Land cover plays a crucial role in mitigating the climate at the local level. Dense vegetation offers a higher resilience potential by creating its own microclimatic conditions. The role it plays in mitigating the local climate, including by maintaining the atmosphere humidity, plays a crucial role also allowing the provision of other ecosystem services.

However, global warming and local human actions threaten forest ecosystems, while in tropical areas, the forest canopy is increasingly endangered by rising temperatures. The risk of reaching a critical point beyond which the trees’ canopy survival could be endangered is not excluded in the medium- or long term. In this background, the reduction of forest density and biodiversity affecting the forest ecosystems’ resilience represents a high risk.

It is expected that global warming will increasingly challenge plants’ survival capacity and impact the water cycle. Biodiversity is a central element contributing to the resilience of ecosystems and of the services they provide.

4.3.2 Ecosystems’ resilience and biodiversity

Biodiversity plays a crucial role in ecosystems’ resilience, as well as in populations’ capacity to adapt to changing conditions. In the background of global warming, biodiversity is an important factor to be considered to understand the challenges triggered by global warming and local changes.

Interspecific and intraspecific biodiversity, playing interrelated complementary roles, should be distinguished.

Interspecific biodiversity is related to a number of different living species dwelling within an ecosystem. It allows to regulate mechanisms between species, including pest control. Synergies are also important like mycelium prolonging a plant’s roots while also providing food for insect larvae that burrow tunnels aerating soil layers, the same way earthworms do. Heterogeneity in trees will also limit the speed at which pests or diseases may spread, thus also participating in regulation mechanisms.

It is also necessary to make the link between the loss of biodiversity of ecosystems on the one hand and the loss of biodiversity within cultivated species on the other. Seasonal temperature changes and climate instability also affect ecosystems which, as they become impoverished, lose resilience and potential for climate mitigation and population regulation among different species.

Intraspecific biodiversity reflects the diversity of physiological expression among different individuals within the same species. The expression of genetic diversity is complex because it is not the result of the simple sum of genes and of the proteins, they are coding for, but as well of multiple interactions among the molecules thus produced. This diversity allows individuum to resist disease while others do not, but have other comparative advantages; the genetic pool among the species is preserved as long as the population remains important enough.

The expression of the biodiversity in plants is, for example, illustrated by the fact that not all seeds will germinate at the same time according to external conditions and not all in the same year, thus increasing the plant’s chance to survive and spread even after a few drought years in the Sahel.

On the contrary, productivity implies that all seeds germinate at the same time, make flowers, and are ready for harvest in a synchronized manner. Modern agriculture, whether for crops or for herding, is therefore efficient at the cost of a higher vulnerability to external factors, like climate, pests, or disease. It is especially vulnerable to the expected unstable climatic environment.

The very low intraspecific biodiversity of cultivated plants reduces the resilience of crops and their ability to resist diseases or extreme events. This trend is especially challenging in the background of climate change.

Thus, the reduction at the same time of interspecific and intraspecific biodiversity strongly reduces the resilience of ecosystems. At the same time, preserving natural ecosystems is of utmost importance to face the growing unstable situation generated by global warming.

Answering the challenge faced by global warming, in the short and medium term, requires solutions developed in synergy, avoiding to the possible extent contradictory measures.

5. Adaptation

5.1 Land cover

Land cover is an important element in mitigating global climate change, as well as the climate at the local level. The IPCC refers to Land Use, Land Use Change and Forestry (LULUCF). Permanent vegetation and organic soil layers allow carbon sequestration, but they play as well an even more important role at the local level in regulating the hydrological cycle, mitigating the local climate, and regulating living populations. Natural ecosystems are more effective in serving those purposes than cultivated forests or fields. They are also more resilient, offering regulatory mechanisms that can replace one another when one fails, while also presenting a biodiversity which limits the risks faced from pests.

Along the Amu Darya in the West of Uzbekistan and along the border of Turkmenistan, the remains of the Badai Tugai Poplar Forest still play some role, mitigating floods, reducing dust in the air, and moderating temperature extremes to a limited extent. The river plays a similar role, as well, influencing temperatures in areas in the vicinity of water retention points.

However, the degraded forest strips reduced in size over time reduced drastically the scope of those services.

Prairie strips, as well as forests and bushes, provide shelter to various insects, which can be beneficial in regulating other harmful insects for crops or contributing to flower pollination, reducing insecticide exposure, and increasing water quality and availability [33]. A bocage landscape will play the same role, while also contributing, to some extent, to climate regulation. However, edges along fields are not sufficient to regulate the local climate providing full benefits like from a natural forest. Forest fragmentation reduces the ecosystem \services’ benefit affecting rain pattern, temperature, wind regime, and biodiversity [20].

5.2 Irrigation techniques as the mitigating factor

Regarding crops, a widely held dominant idea is that there is no high temperature that cannot be compensated by sufficient irrigation and selection of suitable plant breeds, or with the help of genetic engineering. This perspective seems to be predominantly commercially motivated. The bias thus created is not incompatible with the search for solutions, but the food security topic also requires a strategic perspective, establishing the limits of proposed solutions.

Indeed, the limits faced by plants’ physiological limits can be pushed back using irrigation techniques, in particular, by sprinkling in fine droplets.

However, the availability of water is expected to decrease, in particular, due to the reduction in the volume of snowmelt [34] and rainfall events that are less spread out, more violent, and therefore less able to replenish groundwater. Water reservoirs will remain marginal solutions with regard to the loss of mobilized water volumes. In this regard, it should be noted that drawing from groundwater to supply surface water reservoirs, which will also be subject to increasing evaporation, might not be a rational solution. This could locally result in considerable changes in the level of the groundwater with the key to entire ecosystems which could collapse when the roots of the plants no longer reach the water. Wanting to irrigate more to compensate for temperature increases is a headlong rush that will only be possible for a time and in no case can be extended to all existing agricultural production systems.

While high temperatures will gradually and regularly exceed the physiological limits of cultivated plants, thinking of being able to compensate for high temperatures by increased irrigation is a headlong rush. Available water resources are likely to become an increasingly limiting factor while, at the same time, crops’ physiological limits will be more frequently reached.

5.3 Genetic engineering

Genetic engineering can contribute to providing answers to specific faced issues, along the existing genetic pool. However, beyond the risk of reduced intra-specific biodiversity, the interactions between genes are not mastered and the long-term side effects of introduced genes are broadly unknown. In most cases, the transaction cost is not known and not subject to specific studies either. Resistance to some pests or pesticides, as well as crops offering better characteristics for transformation, can be achieved but it might be at the cost of the nutritional value, of a vulnerability to future pests, and of a higher dependency on pesticides.

Thus, genetic engineering implies a specialization with narrow intraspecific biodiversity, which results in a higher vulnerability to a changing environment. Besides, the pool of genes and their expression present a broad diversity which nevertheless does not mean that there are no physiological limits.

Besides, genetic engineering can accelerate the optimization of characteristics present within existing species and to some extent between living species, but it does not create anything new; pushing the limits does not mean the absence of limits. Thus, there are indeed physiological limits, even if these differ from one species to another. Plants fixing carbon on a four-carbon molecule, called C4, offer better heat and drought stress characteristics than plants fixing carbon on a three-carbon molecule, called C3. C4 plants, like sorghum or maize, have the advantage of absorbing more carbon with openings in the leaves, stomates kept smaller, thus also limiting water loss through evapotranspiration. However, those plants are also less resistant to cold temperatures. Besides, it would be rather illusory to think that C3 plants can be transformed into C4 ones, should such a change represent an overall advantage.

6. Conclusions

Humanity is facing an unprecedented challenge triggered at the same time by global warming and by concurrent actions endangering resilience factors. Ecosystems and the biodiversity they embody are crucial to contribute to mitigating the consequences of the faced changes. Ecosystem services contribute to mitigating local climate, regulating hydrological cycles, allowing soft pest control, and contributing to carbon sequestration.

However, ecosystems are themselves endangered at the same time by global warming and by human pressure. The biodiversity implied by ecosystems’ services and resilience still requires a better understanding by decision-makers.

Under temperate climatic conditions, crop growth and production limitations due to high temperatures are new factors which have been marginal in most of Europe and North America until recent years. The tendency in temperate countries is to think that climate change can be coped with or even be beneficial. Those beliefs are misleading and may slow down political decisions crucial in international fora. It is thus of utmost importance to collect factual data and develop research to properly understand challenges and adaptation options.

In this regard, providing solutions to some climate change challenges might be seen as an opportunity to innovate and unlock new sources of profit, but they often have a transaction cost which can bear negative consequences.

Nevertheless, solutions likely to mitigate global warming exist, but those are not universal and are also likely to face limits. Living systems could increasingly be jeopardized if different thresholds should be bypassed. Therefore, a precautionary principle should preferably be applied.

From this perspective, the path of specialization of living production systems, whether for crops or for livestock, at the cost of a loss of intraspecies biodiversity, presents high risks. Having a homogeneous population of plants or animals considerably reduces the resilience of species. Impoverished ecosystems are as well vulnerable.

Genetic engineering is promoted as a possible solution. But the related communication mostly ignores the intrinsic limits of intra- and interspecific genetic potential, and thus of the industrial food production’s inherent fragility.

In arid and semiarid areas, maize, sorghum, or millet presents a higher temperature resistance. However, maize requires more water availability, which may not be suitable for the area. Sorghum presents not only better characteristics and lower water demand but produces also lower yields. Millet presents not only a higher resilience but also even lower yields. In areas facing strong water deficit, a shift toward high-value crops, including fruit and vegetable resilient plants, like pomegranate, on smaller surfaces might also be assessed locally in replacement of less resilient crops.

Worldwide, water resources management will require a long-term perspective, implying difficult arbitrations not only between domestic use and food production, but also between agricultural productions and land areas to receive water.

Land cover, ecosystems’ services, water use arbitration, and technical solutions, among other aspects, require a systemic approach. For achieving such an approach, public policies should play a key role in supporting measures for ecosystem conservation serving the common interest of the public including private actors. Related political choices would require to be supported by detailed impact and transaction costs analysis according to the issue and to the solutions looked at.

Tackling the issue is of utmost importance in order to avoid periods of instability resulting from poorly controlled food security which would lead the world into spirals of degradation.

Acknowledgments

The present publication is based on the work of the author, bibliographic references, and experience drawn from experience in different parts of the world.

Conflict of interest

The author declares no conflict of interest.

Appendices and nomenclature

CO2	carbon dioxide
DD	day degrees – method to estimate plant productivity according to favorable temperature for plant growth
GHG	green house gas
IPCC	intergovernmental panel on climate change
LAI	leaf area index—measuring leaf surface available for evapotranspiration
LULUCF	land use, land use change and forestry
RCP	representative concentration pathway
UV	ultraviolet