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Agriculture and Climate Change

October 10, 2010

The earth’s climate has been relatively stable for thousands of years. We know intuitively that it is hot, humid, and rainy in the Amazon, and that corn grows well in the US Midwest. We know that at a particular altitude we should plant a crop during a certain week of the year because conditions for it are just right then. For most of our memory as humans, our climates have closely oscillated around predictable patterns, and this has allowed us to feed ourselves and flourish.

When a stable climate system is modified beyond its “tipping point,” it gets out of balance and loses its equilibrium. While the system searches for a new set of patterns to stabilize around, variability and uncertainly are the norm. This, in essence, is the nature of the challenge that we are now facing.

EFFECTS OF GLOBAL WARMING ON AGRICULTURE

Agriculture is one of the most weather-dependent of all human activities. It is ironic, then, that a significant percentage of greenhouse gas emissions come from agriculture. Fossil fuel-intensive agriculture is contributing to the creation of the unpredictable weather conditions that all farmers will need to battle in the not-too-distant future.

We are already seeing some climate changes that may be indicative of what’s to come for agriculture:

    * Maple syrup production in the American northeast is suffering. The climate in which maple trees thrive is expected to move about two degrees (of latitude) north to Canada. Maple syrup production is already down by about 10% because of warmer and shorter winters.
    * The southwestern United States is already experiencing a lack of water—without water for irrigation, this area is too dry for large-scale agriculture—and serious desertification is expected to happen within the next few decades. Conditions similar to the Dust Bowl of the 1930s are expected to be the norm in the area by the 2030s.
    * All over the country, we are seeing earlier bird migrations and northward shifts in the ranges of crops and pests.
    * We’re also seeing increased peaks in spring run-off from glacier melt and snow-fed rivers.

The good news is that we can still do something about it. Supporting sustainable agriculture by buying from your local organic farms is a significant action to take. Many small farms are now developing highly productive farming systems with low environmental impact. These are the right kinds of farms for the future. We are likely to achieve better results by learning to collaborate with nature rather than using brute-force to bend it to our will, as is the norm with today’s widespread industrial agriculture practices.

The type of food we eat is as important as how farmers grow our food. Eating “lower on the food chain”—getting less of our protein from meat and more from nuts, seeds, beans, legumes, grains, and vegetables—can make a huge difference in the energy consumption associated with our personal menus.

Effect of elevated carbon dioxide on crops

Carbon dioxide is essential to plant growth. Rising CO2 concentration in the atmosphere can have both positive and negative consequences.

Increased CO2 is expected to have positive physiological effects by increasing the rate of photosynthesis. Currently, the amount of carbon dioxide in the atmosphere is 380 parts per million. In comparison, the amount of oxygen is 210,000 ppm. This means that often plants may be starved of carbon dioxide, due to the enzyme that fixes CO2, rubisco also fixes oxygen in the process of photo respiration. The effects of an increase in carbon dioxide would be higher on C3 crops (such as wheat) than on C4 crops (such as maize), because the former is more susceptible to carbon dioxide shortage. Studies have shown that increased CO2 leads to fewer stomata developing on plants which leads to reduced water usage.Under optimum conditions of temperature and humidity, the yield increase could reach 36%, if the levels of carbon dioxide are doubled.

Further, few studies have looked at the impact of elevated carbon dioxide concentrations on whole farming systems. Most models study the relationship between CO2 and productivity in isolation from other factors associated with climate change, such as an increased frequency of extreme weather events, seasonal shifts, and so on.

Erosion and fertility

Soil erosion and climate change

The warmer atmospheric temperatures observed over the past decades are expected to lead to a more vigorous hydrological cycle, including more extreme rainfall events. Erosion and soil degradation is more likely to occur. Soil fertility would also be affected by global warming. However, because the ratio of carbon to nitrogen is a constant, a doubling of carbon is likely to imply a higher storage of nitrogen in soils as nitrates, thus providing higher fertilizing elements for plants, providing better yields. The average needs for nitrogen could decrease, and give the opportunity of changing often costly fertilization strategies.

Due to the extremes of climate that would result, the increase in precipitations would probably result in greater risks of erosion, whilst at the same time providing soil with better hydration, according to the intensity of the rain. The possible evolution of the organic matter in the soil is a highly contested issue: while the increase in the temperature would induce a greater rate in the production of minerals, lessening the soil organic matter content, the atmospheric CO2 concentration would tend to increase it.

A very important point to consider is that weeds would undergo the same acceleration of cycle as cultivated crops, and would also benefit from carbonaceous fertilization. Since most weeds are C3 plants, they are likely to compete even more than now against C4 crops such as tomatoes. However, on the other hand, some results make it possible to think that weedkillers could gain in effectiveness with the temperature increase.

Global warming would cause an increase in rainfall in some areas, which would lead to an increase of atmospheric humidity and the duration of the wet seasons. Combined with higher temperatures, these could favor the development of fungal diseases. Similarly, because of higher temperatures and humidity, there could be an increased pressure from insects and disease vectors.

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