Climate change concepts

Introduction to climate change

To understand climate change, we first need to understand the difference between weather and climate. Weather refers to the actual atmospheric conditions that are being experienced now. It also includes changes that are forecast over the next few days, for example, in temperature and rainfall. Climate refers to the kind of weather that's typically expected in a region. This includes describing the range of conditions that are possible.

Climate change is a long-term shift in the average weather conditions of a region, such as its typical temperature, rainfall, and windiness. Climate change means that the range of conditions expected in many regions will change over the coming decades. This means that there will also be changes in extreme conditions.

The climate varies naturally from year to year and decade to decade. This is caused by natural processes linking the atmosphere, ocean and land, as well as variations in heat output from the sun. In addition to changes in climate that are caused by natural climate variability, climate change can be caused by human activity. The kind of climate change we are experiencing now is being caused primarily by these human factors.

Causes of climate change

Current climate change is mainly caused by human activities that release greenhouse gases to the atmosphere.

The sun’s energy warms the Earth and the warmed Earth releases heat to the atmosphere. Certain gases in the atmosphere trap this heat and act like the glass of a greenhouse. Such gases are called greenhouse gases.  The main greenhouse gases are water vapour, carbon dioxide and methane. Greenhouse gases absorb heat and radiate some of it back to the Earth, raising surface temperatures. This process is often called the greenhouse effect.

The greenhouse effect is a natural process, but it is being intensified by human activities that increase greenhouse gas levels in the atmosphere, especially carbon dioxide. Increasing greenhouse gas levels in the atmosphere makes it more effective at trapping heat, resulting in overall warming of the earth. Burning fossil fuels (coal, oil, gas) and some industrial processes are the main sources of carbon dioxide. Climate change caused by human activity is referred to as anthropogenic climate change.

Learn more about the causes of climate change and the greenhouse gas effect:

The evidence is clear: the global climate is changing

Each of the last three decades has been warmer globally than any decade on record. From 1948 to 2016 the global average temperature increased by approximately 0.8°C. In Canada, the average temperature increased by 1.7°C during the same time period, about double the global average (Figure 1). Warming has been even stronger in northern Canada. Learn more about climate trends and projections.

Figure 1 : Change in global and Canadian average temperature relative to the 1961-1990 reference period

This figure shows changes in global and Canadian average temperature relative to the 1961 to 1990 reference period. The change in global average temperature (in black) is calculated from Hadley Centre’s sea surface temperature records and the Climate Research Unit’s land surface air temperature records version 4 (HadCRUTv4) dataset, while the change in Canadian average temperatures (in blue) is calculated from the Canadian Gridded Temperature and Precipitation Anomalies (CANGRD) dataset.
Long description

Global temperature shows an increase of about 0.8 degrees Celsius over the 65-years from 1948 to 2013. In Canada, temperature has increased about 1.7 degrees Celsius over the 65-years from 1948 to 2013. The jagged, solid lines show the annual data, while the linear dashed lines show the long-term trend over the 1948–2016 period for both global and Canadian data. The Canadian data are more variable than the global data.


Climate change is already causing impacts on human and natural systems in Canada and around the world. Further changes are inevitable, with larger changes projected for higher emission scenarios. Depending on the region, changes projected for Canada include:

  • higher temperatures
  • shifts in precipitation patterns
  • more frequent and intense heat waves
  • fewer cold snaps
  • rising sea level

More frequent and severe extreme events, such as floods, droughts and wildfire are also a risk.

Learn more about the impacts of climate change:

Climate change mitigation and adaptation

Dealing with climate change requires both mitigation and adaptation actions.

Climate change mitigation is about reducing greenhouse gas emissions from human activities. Learn more about actions to reduce emissions.

Climate change adaptation is about preparing for the current and future impacts of climate change. It means changing our activities and decisions so that we reduce the negative impacts of climate change and become more resilient. Adaptation also involves taking advantage of opportunities from climate change. For example, rising temperatures can increase the length of growing seasons or the varieties of plants that can be grown in different areas. Learn more about adapting to the effects of climate change.

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