Geoscience Reference
In-Depth Information
years has exceeded 7 percent in middle and
high latitudes.
The effects of reduced stratospheric ozone
are particularly important for their potential
biological damage to living cells and human
skin. It is estimated that a 1 percent reduction
in total ozone will increase ultraviolet-B
radiation by 2 percent, for example, and
ultraviolet radiation at 0.30
ozone totals in the 1990s over Palmer Station,
Antarctica (65
S), now maintain low levels
from September until early December, instead
of recovering in November. Hence, the altitude
of the sun has been higher and the incoming
radiation much greater than in previous years,
especially at wavelengths
°
m. However,
the possible effects of increased UV radiation
on biota remain to be determined.
0.30
μ
m is a thousand
times more damaging to the skin than at
0.33
μ
•
Aerosol
loading may change due to natural
and human-induced processes. Atmospheric
particle concentrations derived from volcanic
dust are extremely irregular (see
Figure 2.11
),
but individual volcanic emissions are rapidly
diffused geographically. As shown in
Figure
2.12
, a strong westerly wind circulation carried
the El Chichón dust cloud at an average
velocity of 20m s
-1
so that it encircled the globe
m (see Chapter 3A). The ozone decrease
would also be greater in higher latitudes.
However, the mean latitudinal and altitudinal
gradients of radiation imply that the effects of
a 2 percent UV-B increase in mid-latitudes
could be offset by moving poleward 20km or
100m lower in altitude! Recent polar observa-
tions suggest dramatic changes. Stratospheric
μ
0.5
0.4
0.3
0.2
0.1
0.0
1300
1400
1500
1600
Year (AD)
1700
1800
1900
2000
Figure 2.11
Record of volcanic eruptions in the GISP 2 ice core and calibrated visible optical depth for
AD
1300-2000, together with the names of major volcanic eruptions.
Note that the record reflects eruptions in the Northern Hemisphere and equatorial region only; optical depth estimates depend
on the latitude and the technique used for calibration.
Source: Updated after Zielinski (1995) Journal of Geophysical Research, 100(D10), p. 20,950, Fig. 6.
