The Climate System

The physical climate system involves the earth's atmosphere, land surfaces, and oceans, along with the snow and ice that is so prominent in much of Canada. These components interact with one another and with aspects of the earth's biosphere to determine not only the day-to-day weather, but also the long-term averages that we refer to as 'climate'.

The climate system is driven by energy received from the sun (sunlight). Some of this energy is reflected back into space, but the rest is absorbed by the land and ocean and re-emitted as radiant heat. Some of this radiant heat is absorbed and re-emitted by the lower atmosphere in a process known as the greenhouse effect. The earth's average temperature is determined by the overall balance between the amount of incoming energy from the sun and the amount of radiant heat that makes it through the atmosphere and is emitted to space.

A crucial feature of the climate system is that the sun's energy is not distributed uniformly, but rather is most intense at the equator and weakest at the poles. This non-uniform energy distribution leads to temperature differences, which the atmosphere and ocean act to reduce by transporting heat from the warm tropics to the cold Polar Regions. This non-uniform heating and the resulting heat transport give rise to ocean currents, atmospheric circulation, evaporation, and precipitation that we ultimately experience as weather.

When the balance between incoming and outgoing energy is perturbed, this changes the amount of heat within the climate system and affects all those processes described above that transport heat around the globe. We experience this as changing weather patterns, the consequences of which can be far-reaching since so many human activities have adapted to conditions that have prevailed for long periods of time.