What is climate change?

Diagram depicting pathways of solar radiation.

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Diagram depicting pathways of solar radiation. The sun transmits solar radiation to earth. 46% is absorbed by the Earth's surface. 6% is reflected by the Earth's surface. 23% is absorbed by the atmosphere and released as outgoing solar radiation. 25% is reflected by the atmosphere, and together with radiation from the Earth's surface, is released as outgoing infrared radiation. Infrared radiation emitted by the Earth's surface is absorbed by greenhouse gases, adding heat to the atmosphere.


Climate change is a change in the "average weather" that a given region experiences. Average weather includes all the features we associate with the weather such as temperature, wind patterns and precipitation. When we speak of climate change on a global scale, we are referring to changes in the climate of the Earth as a whole. The rate and magnitude of global climate changes over the long term have many implications for  ecosystems as well as human activities.

A natural "greenhouse effect" regulates the temperature on earth (see figure). Human activities have disrupted the balance of this system. As human societies developed increasingly sophisticated and mechanized lifestyles, the amounts of heat-trapping gases in the atmosphere have been increased. By increasing the amount of these gases, we have enhanced the warming associated with the natural greenhouse effect. Projections of temperature change for the next century indicate that the planet is likely to warm at a rate that has never been experienced in human history.

As concluded by the Nobel Prize-winning Intergovernmental Panel on Climate Change, recent warming of the Earth’s climate is unequivocal.  Best estimates of increases in average global temperatures over the next century range from 1.8 to 4.0 degrees Celcius. In Canada, this could mean an increase in annual mean temperatures in some regions of between 5 and 8 degrees Celcius.

For more information on the basics of climate change, see the following resources: