Geoscience Reference
In-Depth Information
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AN INTRODUCTION TO
THE CLIMATE SYSTEM
Climate dynamics
is the scientific study of how and why climate changes. The
intent is not to understand day-to-day changes in weather but to explain av-
erage conditions over many years. Climate processes are typically associated
with multidecadal time scales, and continental to global space scales, but one
can certainly refer to the climate of a particular city.
Climate dynamics is a rapidly developing field of study, motivated by the re-
alization that human activity is changing climate. It is necessary to understand
the natural, or unperturbed, climate system and the processes of human-induced
change to be able to forecast climate so that individuals and governments can
make informed decisions about energy use, agricultural practice, water re-
sources, development, and environmental protection.
Climate has been defined as “the slowly varying aspects of the atmosphere/
hydrosphere/lithosphere system.”
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Other definitions of climate might also ex-
plicitly include the biosphere as part of the climate system, since life on the
planet plays a well-documented role in determining climate. Anthropogenic
climate change is just one example, but there are others, such as the influ-
ence of life on the chemical composition of the atmosphere throughout its 4.5
billion-year life span.
The word
climate
is derived from the Greek word
klima
, which refers to the
angle of incidence of the sun. This is a fitting origin because solar radiation is
the ultimate energy source for the climate system. But to understand climate
we need to consider much more than solar heating. Processes within the earth
system convert incoming solar radiation to other forms of energy and redis-
tribute it over the globe from pole to pole and throughout the vertical expanses
of the atmosphere and ocean. This energy not only warms the atmosphere and
oceans but also fuels winds and ocean currents, activates phase changes of
water, drives chemical transformations, and supports biological activity. Many
interacting processes create the variety of climates found on the earth.
A schematic overview of the global climate system is provided in
Figure
1.1.
This diagram represents the climate system as being composed of five
subsystems—the atmosphere, the hydrosphere, the biosphere, the cryosphere,
and the land surface. It also depicts processes that are important for deter-
mining the climate state, such as the exchange of heat, momentum, and water
among the subsystems, and represents the agents of climate change.
