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those data. The dominant presence of QBO signals in some types of climate
data has led to marked improvements in forecasting, particularly with regard
to the tropics and subtropics. For example, measures of the QBO are con-
sidered primary variables in seasonal forecasting equations developed for
Atlantic tropical cyclone activity. In a similar fashion, study of global spatial
and temporal variations in ozone variability must address the mechanisms of
the QBO.
However, specification of the actual physical mechanisms by which the
QBO influences climate around the world remains elusive. While we have
achieved a good - albeit not perfect - understanding of how the QBO
operates, there remain many avenues of research on the QBO. In particular,
the incorporation of a realistic QBO into numerical general circulation
models (GCMs) remains unachieved.
In addition, continued identification of a QBO signal in existing climate
data must continue. Because of the relative ubiquity of the QBO in climate
records around the world, some researchers have, unfortunately, tended to
disregard the identification of quasi-biennial signals as ''unimportant'' or
stated that QBO influences have been sufficiently addressed. However, the
usefulness of the QBO in Atlantic tropical cyclone seasonal forecast algo-
rithms demonstrates that the QBO is not only a climatically important
phenomenon but also one whose variations can affect the structure and
development of human society. We need to continue to address the QBO's
causes and influences.
To accomplish that task, more and varied climate records - particularly for
the tropics - must be established. Sadly, the tropics remain a region of
relatively sparse climate observations. Consequently, although new and con-
tinued climate monitoring should be undertaken in the tropics, the study of
long-term paleoclimatic proxy records of sufficient resolution to record QBO
fluctuations should also be analyzed and evaluated. These types of surrogate
climate records might include tree-ring chronologies, equatorial glacial ice-
cores or similar annual resolution records. Study of the QBO should continue
to be an area of investigation for researchers around the world.
3.4 Human activities and problem climates in the tropics
3.4.1 Desertification
The multi-year drought in the early 1970s in the Sahelian zone, a region
extending from West Africa to the Horn of Africa, led to increases in death
and morbidity of humans and livestock and extensive environmental deteriora-
tion. It brought to the fore the process of desertification. Satellite images and
photographs of the landscape and human suffering were widely seen in all types
 
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