Some internal forcings that influence the climate occur on more or less regular cycles. El Niño and La Niña are well-known examples of where changes in the tropical Pacific (both ocean and atmosphere) affect climate elsewhere, including in Canada. These changes affect sea surface temperature and sea level, as well as air temperature and precipitation patterns, particularly in winter.

External forcings include volcanic eruptions and changes in the Sun’s energy output. Volcanic eruptions can influence the climate through the formation of ash clouds that alter the amount of solar radiation that reaches the surface of the Earth and through the emission of carbon dioxide.

Additionally, Ice Ages are the result of slow and predictable changes to the Earth’s orbital cycle that occur over thousands of years. To the extent possible, climate scientists include sources of natural variability in climate models.

This is why climate scientists use a minimum of 30 years of data to draw conclusions about how our climate is changing. Natural variability will continue to affect the climate, alongside the human-induced warming brought on by increased greenhouse gas emissions. It is therefore important to use datasets that are long enough to distinguish between short-term natural variability and long-term climate change.

To learn more about why to use 30 years of climate data, click here.