Agriculture in a changing climate

Agriculture and climate change
Yields of food crops are predicted to decrease by 30-45% by the end of the century for the slowest predicted rate of warming

Timothy D. Schowalter from Louisiana State University, USA, argues that climate change, which should be the top priority for every nation, represents the most serious threat to global food security and social stability.

Food availability and disease have always been the greatest challenges to human survival. Agriculture revolutionised food production and permitted the development of civilisation and our continuing geometric population growth. However, famine has led to wars, destabilised or ended many previous civilisations and remains a threat to modern society as a result of climate change. Although the threat of a warming climate to food security has alarmed scientists and national security experts, much of the general public remains unaware or unconcerned.

Agricultural production has become highly mechanised, but is still subject to ecological processes. Adequate supplies of sunlight, carbon dioxide, water and nutrients are necessary for crop growth. Sunlight and carbon dioxide generally are adequate, and nutrients are typically supplemented as fertiliser. Water, however, is often limiting and could become more so as a result of rising temperatures, which force plants to use more water, and as a result of changes in precipitation patterns as global circulation patterns change.

Precipitation patterns

Precipitation patterns are driven by global circulation patterns that move moisture-laden air from the oceans to terrestrial ecosystems. Mountain ranges are widely recognised for forcing air upward, resulting in condensation and higher precipitation on the windward sides than on the leeward sides.

However, forests also are capable of generating sufficient turbulence and convection to increase local precipitation. Deforestation ranks as a major cause of reduced regional precipitation, resulting in desertification and loss of arable lands in many parts of the world. Increased deforestation for agriculture now appears to have exacerbated droughts that caused the collapse of Mesopotamian and Maya civilizations.

Although irrigation can provide additional water, many major aquafers have been depleted and no longer supply sufficient water, in part because of competition for water between agricultural and increasing urban demands.

Challenges posed by rising temperatures and climate change

Rising temperatures will create additional challenges for food production. Most of the world’s major staple crops (for example, wheat, corn, rice and soybeans) show optimal growth at temperatures below 30°C (86°F). Agronomists and farmers are already seeing declining yields of these crops as temperatures have risen above their optimal ranges. For example, yields of fruit and nut crops in Europe declined 20-35% during the 2003 heat wave when temperature was 3.5°C (6°F) higher than normal.

Yields of food crops are predicted to decrease by 30-45% by the end of the century for the slowest predicted rate of warming. This magnitude of change will force production of many crops to shift toward cooler regions nearer the Poles. Such shifts in crop production pose at least three problems.

First, farmers cannot move with the crops but will need to learn how to grow new crops. Planting new crop species will require changes in sowing depth and density, fertilisation rates and schedules, pollination services, pest management methods, etc. Training and financial resources, and perhaps new machinery, will be necessary. Many farmers will be unable to meet these requirements and will be forced off of their lands. Such agricultural displacement has occurred in many regions at many times, typically as a result of crop failures. Displaced populations often become concentrated in refugee camps, where stress and crowding result in the spread of crowd diseases, such as influenza, malaria, typhus and plague, all of which are capable of straining global health services and becoming pandemics.

Second, land area declines from the Equator toward the Poles: 57% of land area lies within tropical and subtropical latitudes between 25°N and 25°S; 25% of land area lies within the primary agricultural zone at latitudes between 25° and 55° N and S; and only 18% of land area lies in the polar latitudes between 55° and 90° N and S. Thus, shifting agriculture toward the cooler Poles will require quantum increases in yields per hectare to offset the reduced land area available for agriculture. Increasing yields will be a greater challenge, given the problems described above for water limitation and shifting crop production to new areas.

New pests

Finally, agricultural practices will need to address new pests. Crops are already vulnerable to insects and pathogens as a result of their abundance and their breeding to reduce natural defences (that we recognise as bitter or other unpleasant tastes). Abundances of crop-damaging insects and pathogens are increasing as climate warms and crop plants become stressed. Particular insect and pathogen species may or may not shift ranges along with their preferred crops, but stressed crops are vulnerable to a wider variety of insects and pathogens than are healthy plants. This will require new pest management strategies.

Pest management has always been a challenge for agriculture, given the capability of many insects and pathogens to eliminate entire crops, leading to human population displacement. Examples include the potato blight that resulted in starvation and emigration of many Irish farmers in the 1800s and the cotton boll weevil that caused population displacement from the Southern to Western USA during the 1920s.

Globally, insects and pathogens cause crop yield losses of 18% and 16% respectively, despite our most aggressive efforts to control them. Furthermore, insects typically become resistant to commonly-used pesticides within 5-10 years. Pest management will become a greater challenge as we struggle to maintain crop vigour in a changing climate.

Climate change represents the most serious threat to global food security and social stability. If we already fight wars over access to industrial products, how much more will access to adequate food and water lead to social unrest and conflicts? Combatting climate change should be the top priority for every nation.

 

Professor Timothy D. Schowalter

Department of Entomology

Louisiana State University

Agricultural Center

225-578-1827

225-252-5226

tschowalter@agcenter.lsu.edu

http://entomology.lsu.edu/

http://www.lsuagcenter.com/en/our_offices/departments/Entomology/

This article will appear in SciTech Europa Quarterly issue 27, which will be published in June, 2018.

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