Agriculture effects climate change & climate change effects agriculture
The greenhouse effect
The earth is surrounded by an atmosphere through which solar radiation is received. The atmosphere is not static but contains air, in constant motion, being heated, cooled and moved, water being added and removed along with smoke and dust. Only a tiny proportion of the sun's energy reaches earth and some of this is reflected back into space (from clouds etc.). When the radiant energy reaches the land surface, most of it is absorbed, being used to heat the earth, evaporate water and to power photosynthetic processes.
The earth also radiates energy but, because it is less hot than the sun, this is of a longer wavelength and is absorbed by the atmosphere. The Earths atmosphere, thus acts like the glass of a green house, hence the 'greenhouse effect'.
The greenhouse gases (dealt with in subject 3) are those that absorb the Earths radiation and thus contribute to the greenhouse effect, but water is also a major absorber of energy. Where there is an increase in the concentration of greenhouse gases (as with CO2 due to the burning of fossil fuels) this results in an enhanced greenhouse effect - which is of concern as it could lead to climate change (i.e. global warming).
Pause for thought......State 3 mechanisms which could be used to reduce the amount of carbon dioxide in the atmosphere?
Global warming
Global temperatures have risen by over 0.7oC in the last 100 years and eleven of the last twelve years (1995-2006) are the warmest on record. In the UK in 1990s were very warm about 0.6oC warmer than the mean 1961 - 1990 temperature. Warm winters have reduced the number of frosts, and the warmer summers have included record hot spells and high sunshine totals.
Source: Adapted from University of Southampton (2000)
How will climate change effect agriculture
Soil processes
The potential for soils to support agriculture and distribution of land use will be influenced by changes in soil water balance:
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Increase in soil water deficits i.e. dry soils become drier, therefore increased need for irrigation but: |
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Could improve soil workability in wetter regions and diminish poaching and erosion risk |
Crops
The effect of increased temperature and CO2 levels on arable crops will be broadly neutral:
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The range of current crops will move northward |
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New crop varieties may need to be selected |
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Horticultural crops are more susceptible to changing conditions than arable crops |
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Field vegetables will be particularly affected by temperature changes |
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Phaselous bean, onion and sweetcorn are most likely to benefit commercially from higher temperatures |
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Water deficits will directly affect fruit and vegetable production |
How will climate change effect cropping in tropical and arid Countries?
Grasslands and livestock
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There is unlikely to be a significant change in suitability of livestock for UK systems |
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Pigs and poultry could be exposed to higher incidences of heat stress, thus influencing productivity |
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Increase in disease transmission by faster growth rates of pathogens in the environment and more efficient and abundant vectors (such as insects) |
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Consequences for food quality and storage |
Weeds, pests and diseases:
Weeds evolve rapidly to overcome control measures, short lived weeds and those that spread vegetatively (creeping buttercup, couch etc) evolve at the greatest rate:
Grassland and arable weeds could become more tolerant to control measures
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Rate of evolution will increase in hotter, drier conditions and in 'extreme years', could lead to some types of herbicide tolerance becoming more common |
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Possible increase in the range of many native pests, and species that at present are not economically important may become so |
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Surveillance and eradication processes for other significant pests, such as the Colarado beetle will become increasingly important |
Predicted effects of climate change on agriculture over the next 50 years
| Climatic element | Expected changes by 2050's | Confidence in prediction | Effects on agriculture |
| CO2 | Increase from 360 ppm to 450 - 600 ppm (2005 levels now at 379 ppm) | Very high | Good for crops: increased photosynthesis; reduced water use |
| Sea level rise | Rise by 10 -15 cm Increased in south and offset in north by natural subsistence/rebound | Very high | Loss of land, coastal erosion, flooding, salinisation of groundwater |
| Temperature | Rise by 1-2oC. Winters warming more than summers. Increased frequency of heat waves | High | Faster, shorter, earlier growing seasons, range moving north and to higher altitudes, heat stress risk, increased evapotranspiration |
| Precipitation | Seasonal changes by ± 10% | Low | Impacts on drought risk' soil workability, water logging irrigation supply, transpiration |
| Storminess | Increased wind speeds, especially in north. More intense rainfall events. | Very low | Lodging, soil erosion, reduced infiltration of rainfall |
| Variability | Increases across most climatic variables. Predictions uncertain | Very low | Changing risk of damaging events (heat waves, frost, droughts floods) which effect crops and timing of farm operations |
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Source: Climate change and Agriculture, MAFF (2000) |
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Current projections, from the 4th Assessment report by the Intergovernmental Panel on Climate Change (IPCC) published in 2007, suggest that global temperatures will rise between 1.8oC and 4.0oC (best estimate) by 2100 depending on emissions of greenhouse gases and that global sea levels are likely to rise from anywhere between 180mm and 590mm. For further details go to the IPCC website.
Pause for thought......Should farmers take into account predicted climate changes when 'planning for the long term future' of their businesses?
