The differences between weather and climate are substantial. Weather is
a series of atmospheric phenomena that take place each day, such as
rain, snow, humidity, temperature, etc. Weather is dynamic and changes
from one location to the other. On the other hand, climate is the
average weather conditions in one location over many years. The climate
in the Amazon forest is different from the climate in the tundra.
Although weather is dynamic and climate is static, we now know that
scientific evidence shows that the climate is changing by human
activity in many regions around the world. We call this phenomenon
climate change.

Characteristics of Weather

Weather phenomena are basically driven by temperature differences in
the atmosphere caused by the uneven heating of the earth’s surface by
the sun as the earth rotates around it. Weather phenomena are complex,
oscillatory and multi-dimensional. Weather is also chaotic, which means
that it has a sensitive dependence on the initial conditions: small
changes in one region may translate into large changes somewhere else.

Scientists since the 19th century have attempted to forecast the
weather using mathematical equations that represent the bulk of
physical interactions that take place in the atmosphere. These
equations include the equation of motion, wave equation, condensation
equation, and continuity equation, among many others. The combination
of these equations can be considered a model of the atmosphere. To make
a forecast, the equations in this model must be solved simultaneously
and integrated forward in time from a set of initial observations of
the atmosphere and the earth’s surface. With the advent of the computer
in the 1950’s, it has been possible to solve these equations
numerically through a set of approximate differential equations,
leading to the field of numerical weather simulation. Also, recent
improvements in our ability to observe the earth’s surface, its oceans,
and the atmosphere have led to improved starting values for the
forecast. It is through the combination of good observations of the
current state of the atmosphere, accurate equations of how the
atmosphere behaves and high speed computing that the weather and
climate are, to varying degrees, predictable.