Global warming and agriculture are closely interrelated. Global warming is believed to have significant impact on factors affecting agriculture, such as temperature, soil fertility, length of growing season, glacial retreat, carbon dioxide, and precipitation. These factors determine the ability of the biosphere to produce enough food supply for the world's population. The overall effect of global warming on crop growth depends on the balance of these elements. Consideration of the effects of global warming on agriculture can help predict and make the necessary adaptations to make the most out of agricultural production.
Global warming is already affecting potential crop yields in some nations. Wheat yields in recent years were low in Russia, France, India and China compared to what they would have been without rising temperatures. Temperature increases are expected to accelerate in the next decades, affecting food production and increasing its demand, as well. Higher temperatures are related with higher incidences of insect reproduction and disease. These may lead to an increased use of pesticides and herbicides, which has serious implications in human health. Higher global temperatures could also lead to a significant loss of biodiversity due to permafrost melting and shift of habitat of some animal species.
Rising concentrations of CO2 in the atmosphere can have both positive and negative effects. Carbon dioxide rising levels tend to increase the efficiency of plants to utilize photosynthesis, thus accelerating plant growth. This is especially true in wheat, rice and soybeans. According to sjsu.edu, plants grow faster providing that there are adequate levels of CO2, sunlight, water and nutrients. Higher temperatures without the adequate supply of these elements might produce no response or even damage. Under most circumstances the availability of CO2 is the element limiting growth. The effect is even greater for plants growing under low light conditions.
Atmospheric temperatures experienced over the last decades are expected to produce more vigorous precipitation. As a consequence of this, erosion and soil degradation is more likely to take place. While increased precipitation may provide soil with hydration necessary to raise crops, it would also lead to greater risks in arable land erosion. Increase in rainfall would lead to an increase in atmospheric humidity, which combined with higher temperatures could trigger the development of fungal diseases. In addition, increased temperatures and humidity favor the spread of plant diseases.
The continued retreat of glaciers will eventually affect areas that are heavily dependent on water surplus from glaciers. A reduction in water flow will alter the ability to irrigate crops and will affect the flow of summer streams necessary to maintain water reservoirs replenished. It is estimated that approximately 2.4 billion people living in the drainage basin of the Himalayan Rivers will experience floods followed by severe droughts in the following decades. The West coast of North America which receives much of its water supply from glaciers would be affected, as well.
Global warming may increase the amount of farming land in high-latitude regions, as a result permafrost melting. A vast region of permafrost in Siberia and Alaska has started to defrost for the first time since it formed 11,000 years ago caused by more than 3 °C (37 °F) increase in local temperature over the last 40 years. However, permafrost thaw in Russia is expected to produce severe droughts. Sea levels are expected to rise more than 1 meter by 2100, due to ice cap melting. A rise in sea level would affect coastal low lying areas. Low lying regions, including India, Bangladesh and Vietnam would experience major loss on rice crop.
Scientific research and inquiry over the last few decades has revealed an increase in global temperatures and a variation in global precipitation patterns. Studies suggest that global temperatures have risen from 5-7 °C (41-45 °F) in the last century. The contributing factors are subjects of intense debate within the scientific and political spheres; however, the evidence of the phenomenon remains unquestionable. According to the IPCC Second Assessment Report, the projected global warming by 2100 is expected to be between the ranges of 1-3.5 °C (34-38 °F), and a mean sea level rise of 15-95 cm (6-37 inches).