Global Factors 

To understand climate change, we need a basic understanding of the natural global climate system. And a first step is distinguishing between weather and climate. Meteorologists often say that climate is what you expect, but weather is what you get.

Weather is what is happening outside your window right now. It's the day-to-day conditions of our atmosphere that may be described, for example, as calm or windy, sunny or cloudy, or wet or dry.

Climate is the average weather in a particular location over a long period of time. In Canada, weather is measured over a minimum time frame of 30 years to establish what the climate is like for a specific location. The study of long-term weather patterns, not just individual weather events, is very important in determining if the climate is really changing.

The global climate system is regulated by how much energy the Earth receives from the sun minus the amount of energy the planet emits back to space. This is called the global energy balance. As long as the amount of energy coming into the Earth's atmosphere balances the amount going back out to space, the global average temperature will remain stable. If energy gain does not equal energy loss, the Earth's temperature will change. The climate changes when this global energy balance is altered, which has happened naturally over the Earth's history. We have always had some variation in climate.

The global climate system will adjust to several important "external" factors that affect how much energy reaches the Earth. These include changes in the Earth's orbit and changes in output of energy from the sun, as well as rare space catastrophes such as huge meteors hitting the earth's surface. Changes in these factors are responsible for natural climate change.

Once the sun's energy has entered the Earth's atmosphere, what happens to that energy (how much of it is reflected back, how much is converted to heat, and how fast that heat escapes back out) depends on the five main components of the global climate system ­ the:

• Atmosphere
• Oceans
• Land (soils, sediments, rocks that comprise the lithosphere)
• Ice sheets (cryosphere)
• Biosphere (living systems on land and in the oceans)

Natural processes cause changes to the conditions of each of these parts of the environment and these changes also lead to natural climate change. These factors, along with the ever-increasing influence of human activities, interact in intricate ways in a complex system of positive and negative feedback loops.

Major elements of the climate system

How normal is the weather where you live?

Like other countries, Canada gathers data on climate "normals." "Normals is the term used for values of climatic elements (temperature, precipitation, sunshine, etc.) averaged over a fixed, standard period. It was agreed internationally to base climate normals on a 30-year time period. Thirty years is considered long enough to eliminate year-to-year variations.

You can go to the Meteorological Service of Canada's website to find the 30-year climate normals for a monitoring station near you. Then get weather data for your area for the last few years and see how it compares with the 30-year normals.