Participatory Plant Breeding. A method to adapt to climate change in low-input agriculture

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2. Climate change and agriculture 
2.1. Climate change: an overview 
Throughout our planet’s history, climate has always been changing. If we only focus 
on last 650.000 years, we realise that climate conditions on Earth have significantly 
changed many times. So far, there have been at least five major ice ages alternating with 
interglacial ages
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. Climate changes during Holocene
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 have strongly influenced life 
conditions on Earth and the development of human civilization. They have shaped 
cultures and contributed to the invention of agriculture through the domestication of 
plants, as temperatures started raising and vegetation increased (Prentice, 2009). 
Therefore, climate change is not new. However, in recent times, a new type of climate 
change (CC, i.e. the one we are referring to in this work) has appeared. It has peculiar 
characteristics that make it different from all the other changes climate has undergone so 
far, due to its unprecedented rate of change and its anthropogenic nature (IPCC, 2014). 
Indeed, the main driver of CC is human activity (more than 95% of probability) in the form 
of greenhouse gas emissions, largely caused by economic and population growth on 
Earth, that sharply increased since 1750 (first industrial revolution) producing atmospheric 
concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) at the 
highest levels in the last 800,000 years (IPCC, 2014). Moreover, anthropogenic 
alterations in the atmospheric concentrations of aerosols, land cover and solar radiation 
have interfered with the energy balance of the climate system (IPCC, 2007). 
This process has caused a slowing-down of Earth surface’s cooling which, as a 
consequence, has increased global average temperatures and altered rainfall patterns 
since 1950s, with effects on physical and biological systems (IPCC, 2007). These 
changes in climate balance are already having and will further have significant 
consequences on different aspects and dimensions of life on Earth. 
                                                           
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 An ice age is a period of time (millions of years long) when Earth’s surface is covered by ice caps, that 
can be more or less extended. Ice ages are composed of glaciations, when glaciers advance, and 
interglacial periods, when glaciers retreat. During interglacial ages, instead, ice caps disappear from the 
surface of Earth. 
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 The Holocene is the geologic time from about 10,000-7,000 years ago to the present. It began at the end 
of the last ice age and is characterized by the development of human civilizations.
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2.2. Consequences of climate change 
It is not easy to establish whether extreme weather events can be directly traced back 
to CC as their main driver. It is even more difficult to define CC’s impacts as established 
trends. The literature on this topic is fast increasing but more studies are needed in order 
to achieve conclusive results on CC impacts, both in terms of time and space. In fact, it 
is extremely important to understand how these effects will evolve in the future and how 
broad their scope is. What is sure, so far, is that changes in physical and biological 
systems are consistent with the expected effects of global warming, as confirmed by a 
broad range of data and studies (IPCC, 2007).  
Recent climate-related extreme phenomena, such as heat waves, droughts, floods, 
cyclones and wildfires have had negative impacts on ecosystems, food production and 
water supply, infrastructures and settlements. Few positive effects originating from CC, 
such as diversification of social networks and of agricultural practices (IPCC, 2014) can 
also be observed though most of them are outweighed by negative consequences that 
affect most marginalized people, both directly and indirectly. Indeed, these consequences 
are stronger in those environments where economic and social factors contribute to a 
higher level of vulnerability for local population. As stated by IPCC (2014: 6), “People who 
are socially, economically, culturally, politically, institutionally, or otherwise marginalized 
are especially vulnerable to climate change and also to some adaptation and mitigation 
responses”.  
These consequences can be observed in many sectors, ranging from human health 
to subsistence of ecosystems. Given the specific focus of this thesis, after a general 
overview of the relation between climate and agriculture, we will proceed deepening the 
analysis of CC’s most important consequences on primary sector activities.  
2.3. Climate and agriculture 
Agriculture strongly depends on climate: even its very invention can be traced back 
to climate warming among a number of other factors. We know the basic conditions 
influencing plant development are air, light, warmth, humidity (Hatfield et al., 2017). These 
crucially depend on a few climatic factors, such as temperature, solar radiation, water and 
atmospheric CO2 concentration, influencing plant productivity according to the species
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physiology (Fischer et al., 2002). A balanced interaction between a number of factors is 
required in order to maintain a specific plant under optimal development conditions. As 
an example, when temperatures increase, plant’s cells increase their activity too: this will 
require a continuous increase in water supply in order to keep the process working, 
otherwise, problems in development will arise.  
As reported by IPCC (2014), most crop yields are extremely sensitive to daytime 
temperatures around 30° C, especially throughout the growing season. Therefore, 
temperature trends are extremely important for plants’ conditions and even slight changes 
can have detrimental consequences on crops: generally speaking we know that, all other 
things equal, cereal yields decrease with temperature and increase with solar radiation. 
Also, precipitation trends have important impacts on crops: limited water supply will 
decrease yields while an excess of it can have negative effects caused by waterlogging 
(Ceccarelli et al., 2013).  
These examples give an idea of the relationships between climatic factors and 
agriculture: subtle alterations in one or more of the above-mentioned factors can lead to 
important effects on plant yields, both quantitatively and qualitatively. Thus, agriculture 
must comply with significant climate variability.  
2.4. Impacts of climate change on agriculture 
Agriculture is strongly affected by CC. However, defining a clear baseline to assess 
CC’s effects on agriculture is not an easy task, especially because non-climate drivers, 
which are not so easy to quantify, can play a role. Moreover, extreme weather events that 
occurr rarely can hardly be captured by models. Nevertheless, the literature on this topic 
has grown in recent years and many advances have been done. 
According to IPCC (2014), CC has an overall negative impact on crop yields: while 
some positive trends can be observed, especially in high-latitude regions, these are 
generally outweighed by negative effects. We can identify direct and indirect effects. The 
former, also referred to as CO2-fertilization effects, describe the impact of an increase of 
CO2 concentration in ambient air on plants. The latter, also called weather effects, are 
the consequences of changes in solar radiation, precipitation and air temperature.
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As regards CO2, in general an increase in its concentration is connected to increased 
crop productivity. However, different species, varieties and local conditions (such as soil 
fertility, temperature, humidity) can influence plants’ response to this increase (Fischer et 
al., 2002). Moreover, nutritional quality is usually negatively impacted by elevated CO2. 
High ozone (O3) concetration in most cases has a damaging effect on crop yields (Fischer 
et al., 2002). Also increases in nitrogen, whose concentration is expected to increase 
further due to CC (IPCC, 2007), are known to have negative impacts on species diversity, 
contributing to reduce biodiversity (Ceccarelli et al., 2013). 
According to Ceccarelli et al. (2013: 8) the most likely CC indirect effects on crops for 
next years are the following: 
• higher temperatures, which will reduce crop productivity, are certain; 
• increasing frequency of drought is highly probable; 
• increase in the areas affected by salinity is highly probable; 
• increasing frequency of biotic stress
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 is also highly probable. 
Fischer et al. (2002) observed that thermal regimes are changing all over the planet, 
implying future consequences such as an important reduction of boreal and arctic 
ecosystems, an expansion of temperate climate conditions in Siberia and Canada and of 
tropical zones, disappearance of temperate zones in Argentina and Chile, among others. 
All in all, “over 5,000 plant species could be impacted by climate change, mainly due to 
the loss of suitable habitats” (Ceccarelli et al., 2013: 340). 
There is no doubt that “global warming will affect the agro-ecological suitability of 
crops” (Fischer et al., 2002: 9) with specific effects on soil, climate, atmospheric 
constituents, solar radiation, pests, diseases and weeds. Main sources of concern are the 
following: trends of rainfall regimes and water storage, crops’ responses to increasing 
CO2, spread of weeds, pests and diseases, intrusion of saltwater as a consequence of 
sea level rise, threats to biodiversity, adaptation to extreme weather events, increase of 
GHGs. One of the most challenging features of current CC is its unpredictability: climate 
models, in fact, cannot predict exactly what consequences CC will have, with which 
intensity, nor when and where these will happen.  
                                                           
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 A biotic stress is the result of a damage caused by living organisms, e.g. bacteria, viruses, fungi, parasites, 
beneficial and harmful insects, weeds, and cultivated or native plants (Flynn, 2003).
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Moreover, CC impacts are expected to disproportionately affect  agriculture-based 
households in LDCs, which are highly vulnerable to CC mainly due to the following 
reasons: 
• strong dependence of rural populations on natural resources and climate factors 
due to high rates of employment in agriculture and limited access to land, modern 
agricultural inputs, infrastructure, education (IPCC, 2014); 
• climate models predict most negative CC effects to take place in Sub-Saharan 
Africa, the Tropics and other risk-prone areas such as low lands, potentially 
negatively impacted by rising sea levels (Kreft et al., 2017)
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; 
• high level of food insecurity, which can be only worsened by the interaction between 
CC effects’ reducing agricultural production and demographic increase (Ceccarelli 
et al., 2013). 
These processes pose new challenges to agriculture, which should be addressed 
through dynamic and innovative approaches, able to tackle continuous and almost 
unpredictable changes in environmental conditions and suitable to be taken by those 
communities who suffer the most from CC negative effects. Hence, what is needed is 
identifying and putting into practice adaptation and mitigation
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 mechanisms capable to 
enhance agriculture’s resilience level.  
All these measures have to be context-specific, as it is impossible to find a single 
strategy able to cope with the needs and problems of any specific region and community. 
Agro-biodiversity, in the forms of inter- and intra-specific crop diversity, can represent 
a key to adaptation processes: “increased crop diversity should positively enhance crop 
resilience in the ever-changing face of climate-induced stress, resulting in improved crop 
performance and enhanced food security” (Murphy et al., 2014: 3). 
In this alarming picture, what worries even more is the interaction between CC 
potential effects and the trend of uniformity in agriculture, which has become more and 
more common since Green Revolution (1960s-1970s). Agro-biodiversity is a strong 
                                                           
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 According to Kreft et al. (2017: 4), “of the ten most affected countries (1996–2015), nine were developing 
countries in the low income or lower-middle income country group, while only one was classified as an 
upper-middle income country”. 
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 Adaptation involves all those actions aimed at adjusting to actual or expected CC effects. Mitigation refers 
to efforts to reduce or prevent climate change determinants, such as emissions of GHGs.