Agriculture Reference
In-Depth Information
It is difficult to predict how much the ozone layer will be depleted in the future. The World Meteorological
Organization predicts that if the Montreal Protocol is adhered to fully, the ozone layer could be restored to its pre-
1980 levels by the middle of the 21st Century (WMO, 2003). In the meantime, enhanced UV irradiation will be a
fact of life, and no one knows for sure that UV irradiation will not continue to increase.
There is disagreement in the scientific community about the consequences of increased UV exposure. Certainly,
even slight increases in exposure to UV can be harmful to plants. Too much UV can damage leaf cells, inhibit
photosynthesis and growth, and promote mutations. Different crop plants have varying levels of sensitivity to
increased UV exposure, but even if only a few crops suffer decreases in yield, the effect on worldwide food production
could be dramatic. In addition, if UV radiation increases significantly, agriculture all over the world could be
threatened, in addition to natural terrestrial and marine ecosystems.
Wavelength in nanometers
10
100
1000
10,000
100,000
1,000,000
1
X-rays and gamma rays
Ultraviolet light
Infrared light
Radio waves
Visible light (390 - 760 nm)
Range of solar radiation not substantially filtered
out by the atmosphere
FIGURE 4.1
The electromagnetic spectrum.
The sun emits the full spectrum of electromagnetic energy, but the atmosphere reflects
and filters out most of the shortwave radiation, much of the infrared, and the longest wavelength radio waves. A relatively narrow
band of energy centered on the visible light spectrum reaches the earth's surface mostly unimpeded.
Reflected
Re-radiated
Atmosphere
Absorbed
Re-radiated
Reflected
Transmitted
Reflected
Re-radiated
Absorbed
FIGURE 4.2
The fate of light upon reaching the earth.
Transmitted light from the sun is mostly in the visible-light range; reradiated
energy is mostly in the infrared range.
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