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4.4 Growing seasons and agriculture
It is estimated that the growing season has lengthened by nearly eleven days since the 1960's In Northern Europe leaves emerge six days earlier in the spring and they last five days longer in the autumn.
  1. Other changes are plants growing at higher altitudes in the mountains, and birds lay eggs earlier in the spring.
    Butterflies have extended their range northwards in Europe as well as in North America .
    "Crop and livestock farmers who have sufficient access to capital and technologies are expected to adapt their farming systems to climate change." (TAR, Chapter 5)
    Increased CO2 in the air have a fertilizing effect on many plant species.

    Photo: Åke Bjørke
  1. "With moderate temperatures, long-term doubling of current ambient CO2 under field-like conditions leads to a 30% enhancement in the seed yield of rice, despite a 5-10% decline in the number of days to heading. The grain yield of CO2 -enriched rice shows about a 10% decline for each 1°C rise above 26°C. This decline is caused by a shortening of growth duration and increased spikelet sterility. Similar scenarios have been reported for soybean and wheat."
  1. What happens with an increase in temperature of e.g. 2°C. ?

    Increasing temperatures will likely affect major crops such as tea in Kenya.
    Major impacts on food production will come from changes in temperature, moisture levels, ultraviolet (UV) radiation, CO2 levels, and temperatures may cause expansion of production into higher elevations.

    The grain filling period may be reduced as higher temperatures accelerate development, but high temperatures may have detrimental effects on sensitive development stages such as flowering, there by reducing grain yield and quality.

    Crop water balances may be affected through changes in precipitation and other climatic elements, increased evapotranspiration, and increased WUE resulting from elevated CO2.

    Staple crops such as wheat and corn that are associated with subtropical latitudes may suffer a drop in yield as a result of increased temperature, and rice may disappear because of higher temperatures in the tropics (Odingo, 1990).

    It is suggested that major changes in farming systems can compensate for some yield decreases under climate change, but additional fertilizer, seed supplies, and irrigation will involve extra costs.

    Graphic: UNEP/GRID-Arendal
  1. Increasing temperatures threaten some crop varieties.
    In Uganda, the total area suitable for growing Robusta coffee would be dramatically reduced with a temperature increase of 2 degrees Centigrade.
    Only higher areas would remain suitable for coffee production, the rest would become too hot to grow coffee.
    This study shows the vulnerability of developing countries, whose economies often rely heavily on one or two agricultural products.



    Graphic: UNEP/GRID-Arendal
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The Greenhouse effect, Climate Change and the road to sustainability
1. 1 Greenhouse effect
2. 2 Science
3. 3 Mitigation
4. 4 Impacts
5. 5 Solutions?