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Agricultural production systems are facing increasing competition from other sectors for limited natural resources. The availability of these resources and their quality are also being affected by unsustainable management practices and changing climatic and weather conditions. To respond to this situation, the agriculture sectors must improve their sustainability performance and adapt to the impacts of climate change in ways that do not compromise global efforts to ensure food security for all. These challenges are intimately and inextricably related, and need to be addressed simultaneously.

The concept of sustainability has three dimensions: economic, environmental and social. A sustainable farming system should be a profitable business that creates mutually beneficial relationships among workers and the surrounding community, and contributes to the sound management of the land and other natural resources. SDG 2, 'End hunger, achieve food security and improved nutrition and promote sustainable agriculture', makes it clear how important the promotion of sustainable agriculture is to the 2030 Agenda for Sustainable Development. As their name suggests, the SDGs have a strong focus on all the dimensions of sustainability.

The heightened emphasis on sustainability in agriculture is due to the fact that the recent achievements in agriculture, which have led to major improvements in productivity that have enabled food production to keep up with population growth, have often come at high social and environmental costs. For example, FAO (2011a) estimates that, as a result of the combined demands of agriculture and other sectors, more than 40 percent of the world’s rural population lives in river basins that are classified as water scarce. Each year, soil erosion destroys 10 million hectares of cropland. Forty percent of this loss is due to tillage erosion (Pimentel, 2006). Genetic erosion, which is partly a result of intensive agricultural production systems that use fewer and more genetically uniform crop varieties, has created a situation where genetic vulnerability (when a widely planted crop is uniformly susceptible to a pest, pathogen or environmental hazard as a result of its genetic constitution) threatens agricultural production in 60 countries. Progress in raising agricultural production has been made largely by producers that have access to inputs and markets, and secure rights to use the land and other resources, which many smallholder producers, especially women, do not have. As a result social inequity has increased in many rural areas, and food security in agricultural communities in developing countries has remained stubbornly high. All of these collateral effects of modern agricultural production are now jeopardizing the accomplishments of past development strategies, and have pushed sustainability to the very heart of the 2030 Agenda for Sustainable Development (FAO, 2016b).

Sustainable agricultural development is designed to enhance productivity, maintain or restore the soil fertility, increase the efficiency in the management of water and energy resources, conserve and harness genetic resources for food and agriculture, strengthen the rural livelihoods, and promote equity and social well-being. The key to achieving these multiple objectives is the adoption of a systems approach. This involves an examination of the food system as a whole and promoting integrated and harmonized development strategies across the different agricultural sectors and along all the stages of the food value chain in ways that take into account the synergies and the trade-off among the different dimensions of sustainability (FAO 2016b). A greater emphasis on system and integrated approaches is expected to reduce the conflicts over resources, optimize the allocation and use of natural and financial resources and increase the efficiency of the agricultural production systems and the food supply chain. 

Sustainable agriculture development can also contribute to increasing economic equity. Introducing sustainable technologies and practices in the agriculture sectors is relatively inexpensive compared to other sectors. In many developing countries, with large numbers of resource-poor producers, it is the only viable development alternative. Sustainable agricultural development is expected to deliver more benefits to impoverished smallholder farmers and increase the resilience of communities that are highly vulnerable to extreme weather events associated with climate change. 

Sustainable agriculture development is a process that requires the participation of a large share of the rural population. This participation must be facilitated by supportive policies, institutions and financing, that taken together can create an enabling environment for climate-smart agriculture at local, national and international levels. Making the transition to sustainable agriculture production systems and food value chains requires a collective effort that involves all stakeholders in both the design and the implementation of policies, programmes and investments.

Despite concerted efforts to combat food insecurity, the number of chronically undernourished people in the world is estimated to have increased from 777 million in 2015 to 815 million in 2016 (FAO, IFAD, UNICEF, WFP and WHO, 2017). Nevertheless, over the last fifteen years, progress has been made; in 2000, the number of undernourished people stood at 900 million. However, progress remains unevenly distributed across different regions. 

Climate change will have negative impacts on all dimensions of food security (FAO, 2016a). The impacts of climate change on agriculture will be the key channel through which climate change will affect food security. Other impacts of climate change, such as the increased frequency of severe weather events in urban areas will also contribute to food insecurity.

When considering the impacts of climate change on food security and designing strategies to address these impacts, it is critical to understand the different dimensions of food security. FAO has defined four dimensions of food security:

• food availability,
• economic and physical access to food,
• food utilization, and
• stability over time (vulnerability and shocks). 

Climate change directly affects food availability through its increasingly adverse impacts on crop and animal productivity and health, and fish stocks, especially in sub-Saharan Africa and South Asia, where most of world's food insecure live. For impoverished agricultural producers, a secure supply of food is not only a basic need, it is the single, and often fragile, means they have for earning an income and maintaining their livelihood. Producers who suffer lower yields will see their ability to access food decline, as they have less money available to purchase food. In addition, declines in the food supply associated with climate change, will likely be reflected in higher food prices. This would affect both the urban and rural poor, as they spend much higher shares of their income on food. Also affected will be poor smallholder family farmers, most of whom are net buyers of food (World Bank, 2008). Climate change can also have impacts on the way food is utilized. Some studies indicate possible impacts in terms of food quality, nutrition and food safety (e.g. Myers et al., 2014). Increased climate variability affects the stability of food supplies and food prices through their impact on production. Climate-related shocks can affect those who are not poor but are nevertheless vulnerable and can drag them into poverty, if, for example, a flood destroys a microenterprise, a drought decimates a livestock herd, or contaminated water makes a child sick. These events can erase decades of hard work and the accumulation of assets, and cause irreversible damage to people's health. 

Climate change will be just one of several factors that will drive future trends in poverty and food insecurity. Poverty and food insecurity, and the severity of climate change impacts on them, will be determined by overall socio-economic development. A recent World Bank study has estimated poverty levels in 2030 under different climate change and policy scenarios. The study found that under a high climate change impact scenario, the number of people in extreme poverty increases significantly in 2030 by 122 million people; in a scenario of prosperity the increase would be just 16 million. However, the future impacts of climate change on poverty will also be determined by policy choices and targeted adaptation strategies (Hallegatte and Rozenberg, 2016).

Climate change will affect the agricultural sectors in many ways, and these impacts will vary from region to region. For example, climate change is expected to increase temperature and precipitation variability, reduce the predictability of seasonal weather patterns and increase the frequency and intensity of severe weather events, such as floods, cyclones and hurricanes. Some regions are expected to face prolonged drought and water shortages. The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (IPCC, 2014) also points out that changes in climate and carbon dioxide concentrations will enhance the distribution and increase the competitiveness of important invasive weeds. As a result of climate change, some cultivated areas may become unsuitable for crop production, and some tropical grasslands may become more arid. In sub-Saharan Africa alone, projections predict a loss of 10-20 million hectares of land available for double cropping systems and 5-10 million hectares for triple cropping systems as a result of climate change (Fischer et al., 2005; Schmidhuber and Tubiello, 2007). Those changes will have direct effects on agricultural production, which, in turn, will have economic and social consequences that will be reflected in the prevalence of food insecurity. The impacts range from yield reductions, increased yield variability, displacement of crops and livestock breeds, and the loss of agricultural biodiversity and ecosystem services. A large body of evidence points to a prevalence of negative outcomes, with many agricultural systems becoming less productive and some plant and animal species disappearing (e.g. Tirado et al., 2010; Porter et al., 2014 and HLPE 2012a). Among the most affected areas are economically vulnerable countries that are already food insecure, and food-exporting countries. Consequently, climate change is expected to increase the gap between developed and developing countries, which will be further exacerbated by the relatively lower technical and economical capacities of developing countries to respond to new threats (Padgham, 2009). 

In terms of impacts, it is necessary to differentiate between increased variability and slow onset changes. The potential impacts of increased variability are often less emphasized than slow onset changes for a variety of reasons. This is because these impacts are less well known even though they will be felt first (HLPE, 2012a). The impacts of increased variability are situated between the much emphasized category of ‘extreme events’, and the much more ‘easier to grasp’ business-as-usual category of actual variability. It is important to distinguish between these two categories of impacts to highlight two ways to adapt, each with different time ranges: increasing resilience now to be prepared for more variability, and increasing adaptive capacities and preparedness for slow onset changes. Furthermore, being prepared for increased variability is also a way to prepare for any other change, whatever it may be.

The agricultural sectors are a major contributor to global greenhouse gas emissions. As indicated in the overview this module, FAO estimates that emissions from the AFOLU sector directly accounted for 22 percent of total global emissions in 2010 (FAO, 2016a). These emissions are the result of natural processes and agricultural practices, which makes them more difficult to control and measure. If the emissions caused by energy use within the food value chains are included, the share of greenhouse emission increases to more than 30 percent (FAO, 2011b). As an integral part of the economy, the agricultural sectors have been called upon to contribute to mitigating climate change (UNFCCC, 2008). The critical question is how and to what extent agriculture production systems and food systems can contribute to climate change mitigation without compromising food and nutrition security. 

Agricultural production systems and food systems can contribute to mitigating climate change and still keep their focus on a ‘food security first’ objective in a number of other ways. One way is to improve efficiency by decoupling production growth from emissions growth. This involves reducing emissions per kilogram of food output. Also, if the crop and livestock production and forestry sectors are managed sustainably, they can act as 'sinks', capturing and storing carbon in biomass and soil. Their management can play an essential role in managing climate change especially in the long term (Gitz, 2013). The IPCC estimates that nine-tenths of the global mitigation potential of agriculture is linked, not to reduction of agricultural greenhouse gas emissions, but to managing land carbon stocks. This calls for overall improvements in soil fertility, which involves enhancing soil carbon sequestration, reducing tillage, improving grazing and manure management, and restoring organic soils (especially peatlands) and degraded lands. It should be noted that within food value chains, reductions of emissions at some stages could lead to increases elsewhere. For instance, depending on the efficiency of production systems, shorter food chains could reduce emissions form transport but increase emissions from agricultural production. The impact of mitigation interventions at the different stages of the food value chain will depend on the level of development the country has reached. When looking at challenges and opportunities to reduce greenhouse gas emissions in the agriculture sectors, it is paramount to look beyond the production stage, and consider the whole food value chain and the relationship agriculture production systems have with other land uses, especially forestry.