Climate Change 101

Climate change is a long-term shift in overall weather conditions over time. It is measured by changes in temperature, precipitation, wind, snow cover and other indicators. When we speak of climate change on a global scale, we are referring to changes in the climate of the earth as a whole.

While the earth's climate is naturally variable, its average state is regulated by factors such as the earth's orbit around the sun and the natural greenhouse gas effect. In fact, the earth would not be warm enough to sustain life without the natural greenhouse gas effect. The atmosphere is like a blanket, or greenhouse, trapping heat escaping from the earth's surface. The principal natural greenhouse gases are water vapour and carbon dioxide. By burning fossil fuels such as coal, oil and natural gas, we release more carbon dioxide into this blanket. Changing land use, such as deforestation and the conversion of land to agricultural use, has also contributed carbon dioxide to this blanket.

Causes of climate change can be divided into two categories ­- those related to natural causes and those created by humans.

Natural Causes

The climate can be affected by natural factors that are external to the climate system, such as changes in volcanic activity, solar output and the earth's orbit around the sun. It can also be affected by natural internal changes, such as variations in ocean currents, which can influence the climate for periods of decades.

Human Causes

Climate change can also be caused by human activities, such as the burning of fossil fuels and the conversion of land for forestry and agriculture. Since the Industrial Revolution began about 250 years ago, climate change due to human influences has increased significantly because of the combustion of fossil fuels (such as oil, natural gas and coal) and, to a lesser extent, because of changes in land use practices. As a result, the amount of heat-trapping gas in the atmosphere has increased, enhancing the warming capability of the natural greenhouse effect.

It is this human-induced enhancement of the greenhouse effect that causes the most environmental concern because it has the potential to warm the planet at a rate that has never been experienced in human history, causing glaciers to retreat, sea levels to rise, and climatic zones to shift. Depending upon emissions during the 21^st century, most experts agree that average global temperatures could rise by one to six-and-a-half degrees Celcius over this century. In Canada, this could mean an increase in annual mean temperatures in some regions of more than double the increase in the global average.

But climate change is more than just a warming trend. Increasing temperatures will lead to changes in many aspects of weather, such as wind patterns, the amount and type of precipitation, and the types and frequency of severe weather events that may be expected to occur. Such climate change could have far-reaching and/or unpredictable environmental, social and economic consequences.