What is Climate Change?

Climate change is a shift in the ‘average weather’ that a given region expWater Drops on Leaferiences. This is measured by changes in temperature, wind patterns, precipitation, and storms.

It is not unusual for the Earth’s climate to vary – historically there have been numerous cycles of warming and cooling. We are currently in a warming cycle. For this reason it may seem there is no need to worry about the present climate. However, in addition to the present period of warming, humans are contributing large amounts of heat-trapping chemicals (called greenhouse gases) through the burning of fossil fuels. These gases cause the rate of global climate change to increase. These two factors contributing to climate change have the potential to significantly impact water resources in Canada, and around the world.

Understanding The Global Climate System

On a global scale, climate is largely regulated by how much energy the Earth receives from the sun and how much energy it releases back to space. The global climate is also affected by other flows of energy within the climate system itself. These energy flows are regulated by:

• the atmosphere – which provides gases, aerosols, clouds and winds
• the oceans – which distribute heat through currents
• precipitation - rain, snow or ice
• water - lakes and rivers, and
• land - which reflects or absorbs energy from the sun.

Changes to any of these elements can affect the balance of the entire system, causing the climate to change. A good example of this is the weather phenomenon known as El Niño/Southern Oscillation. Above-average Pacific Ocean water temperatures have affected the patterns of tropical rainfall from Indonesia all the way to the west coast of South America, a distance roughly equal to half of the world's circumference. These changes in tropical rainfall have, in turn, affected weather patterns around the globe.

Understanding Climate Change

Climate Change is the change in climate over a time period that ranges from decades to centuries. The term refers to both natural and human-induced changes. The term “climate variability” refers to shorter term (years to decades) fluctuations in climate such as those caused by El Niño/Southern Oscillation.

There is international scientific agreement that the world is getting warmer. By examining climate records, scientists have determined that the temperature of the air at the Earth's surface has warmed by approximately 0.6°C since the late 19th century. Evidence from tree rings, tropical corals and Greenland ice cores indicates that, at least for the Northern Hemisphere, the 20th century was the warmest of the past 1,000 years, with the 1990s being the warmest decade of the millennium. Furthermore, it's getting ever warmer - most experts agree that average global temperatures will rise by 1.4°C to 5.8°C over the next century.

The changes occurring now are, for the most part, a direct result of the production of greenhouse gases and aerosols from human activities. These include carbon dioxide (CO2), methane (CH4), nitrous oxides (N2O) and halocarbons (such as chlorofluorocarbons). Consequently, in 2001 the Intergovernmental Panel on Climate Change concluded that there is new and stronger evidence that “most of the warming observed over the last 50 years is attributable to human activities”.

Adapted from Pollution Probe's Climate Change and Human Health Primer