232 CHAPTER 9 Global Atmospheric ChangesOzone layer30 km (19 mi)15 km (9 mi)1970 1980 1990 2000 2006
YearDobson units of ozone270280290300310320330340010203040Melanoma rate
per 100,00 in populationozonemelanoma(^0100) Total Ozone (Dobson units) 200300400500600700
NASA/Goddard Space Flight Center
Based on data from New Zealand National Institute of Water and Atmospheric Research
Ozone layer
a. Stratospheric ozone absorbs about 99 percent of
incoming solar ultraviolet (UV) radiation, effectively
shielding the surface.
b. When stratospheric ozone is present at reduced levels,
more high-energy UV radiation penetrates the atmosphere
to the surface, where its presence harms organisms.
c. Ozone depletion. A computer-generated image of part of the
Southern Hemisphere, taken in September 2012, reveals ozone
thinning (the purple area over Antarctica). The ozone-thin area is
not stationary but moves about as a result of air currents.
d. Average yearly ozone column over New Zealand and
annual melanoma rate in New Zealand, 1970 to 2006. Located
in the Southern Hemisphere, New Zealand is particularly
vulnerable to increasing UV radiation due to ozone thinning.
Melanoma is a common form of skin cancer that can be caused
by exposure to UV radiation.
Environmental InSight The ozone layerÊ UÊ }ÕÀiÊ°£x ✓✓THE PLANNER
232 CHAPTER 9 Global Atmospheric Changes
Interpreting Data
In what year did the average
yearly column of ozone above
New Zealand first drop below
300 Dobson units?