What is Climate Change?
The Earth's Climate System
Two of the most important natural forces controlling global climate are how much of the sun's (solar) energy reaches the earth's surface and how much of that energy is retained
in the atmosphere. When these forces are in balance, the global climate system is stable. The climate system involves the natural reactions between the gases in the atmosphere, the planet's water and ice,
the land and living things, and solar energy.
The chemistry of the atmosphere is very important in determining how much of the incoming solar energy is retained and how much escapes back to space. Several important gases in the atmosphere act like
a blanket around the earth, helping to trap some of that solar energy. These are water vapour, carbon dioxide (CO2), methane (CH4), nitrous
oxide (N2O) and other trace gases.
They are known as "greenhouse gases" because
they keep the planet warm, somewhat like the glass in a greenhouse keeps plants warm.
The atmosphere's ability to retain solar energy makes our planet habitable. Without it, the global average temperature would be about minus 18°C rather than the plus 15°C we enjoy. The climate
of the earth has changed dramatically over geological time, but it has been fairly stable over the last 10,000 years. This period of stability has supported the development of our complex human societies.
Note: "Climate" is the average weather — temperature, wind patterns and precipitation — that a region experiences. When we talk about "global climate change," we are referring to changes
in the climate of the entire planet.
Global Atmospheric Warming
Fossil fuel burning has led to a significant increase in the amount of greenhouse gases in the atmosphere. Scientists have determined, for instance, that
human activities since the Industrial Revolution in the mid-1800s have resulted in a large increase in carbon dioxide — a powerful greenhouse gas — mainly because of the burning of fossil
The current global average of carbon dioxide in the atmosphere is higher than at any time in the last 420,000 years, and likely the last 20 million years. The speed of this increase is unprecedented
during at least the past 20,000 years.
Scientists link the human-caused increase in carbon dioxide and other greenhouse gases with a recent warming of the global atmosphere, known as "global warming." The Intergovernmental
Panel on Climate Change, established by the United Nations to assess scientific information related to climate change, has concluded that greenhouse gas emissions from human activities are altering
the atmosphere in ways that are expected to affect the global climate system.
The six greenhouse gases included under the international Kyoto Protocol are: carbon dioxide (CO2), methane (CH4),
nitrous oxide (N2O), sulphur hexafluroide (SF6), hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs).
Scientists are able to lump the effect of these six gases together by figuring out their carbon
So when we talk about "carbon
footprint" and "carbon neutral", for example, we are referring to all the major greenhouse gases, not just carbon dioxide.
Global Atmospheric Warming and Global Climate Change
Global atmospheric warming affects many parts of the global climate system, including the temperature of surface air, land and water conditions; precipitation; evaporation; and wind patterns. It also affects
aspects of the ocean system, including temperature, currents and sea level.
Evidence of global climate change is widespread and clear:
- The increase in temperature observed in the northern hemisphere during the 20th century is the largest of any century during at least the past 1,000 years.
- Global average temperature rose by 0.74°C over the 20th century.
- The 1990s was the warmest decade, and 1998 and 2005 were the two warmest years ever measured with instruments (since 1850).
- Snow cover has decreased by 10% since the 1960s.
- Mountain glaciers in the nonpolar regions have retreated during the last 100 years.
- Lakes and rivers are now free of ice earlier in the spring.
- The overall average ocean temperature has increased since the late 1950s.
- Global average sea level has risen between 10 to 20 centimetres over the past 100 years.
Global climate change manifests itself differently from one region to another. Changes in regional climate drive changes in physical systems (e.g., the timing and volume of river flows), as well as
biological systems (e.g., the date that buds or leaves emerge). Such changes can also have impacts on our society and economy.
At the regional level, climate change can include:
- a change in average climate, such as average annual temperature and precipitation;
- a change in natural climate variability, for example the frequency of cool, wet La Niña years, and warm, dry El Niño years in the Pacific Northwest; and
- a change in the frequency of severe weather events such as heat waves, drought, and high-intensity rainfall, as well as weather-related events like flooding and coastal storm surges.
In addition, global atmospheric warming may in future trigger severe and abrupt changes in regional climate.
Future Climate Change
Using computer models, scientists are able to estimate how much the earth will continue to warm over the next 100 years, depending on how much human activities continue to alter the composition
of the atmosphere. Depending on the choices people all over the world take in reducing their reliance on fossil fuels, the best estimate projections for global average-temperature increase are between
are 1.8°C to 4.0°C over this century. To put these figures in perspective, the earth's average temperature during the last ice age was only 5°C colder than at present.
A rise in average global temperature doesn't mean that every region of the world will warm uniformly. The vast ocean areas will warm gradually and the continental areas more dramatically. Some areas
will likely become wetter, some drier, some hotter, and some places will be cooler. We can expect more extreme warming in the higher latitudes (such as Canada) and the interior of continents (i.e., noncoastal
The excess greenhouse gases already in the atmosphere will continue to affect the global climate for centuries. Efforts to reduce greenhouse gas emissions now and in the future will reduce but
not prevent climate change.
See the B.C. Climate Change Secretariat's Glossary to learn about the major terms used in discussing climate change.