Climate Change
NEW Are you looking to learn about climate change? how it works? what its causes and impacts are?
If so, you should check out ClimateInsights101: learning resources from the Pacific Institute of Climate Solutions at UVic.
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, methane, nitrous oxide 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.
"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.
Atmospheric Warming and Global Climate Change
Global atmospheric warming affects other parts of the global climate system, including the temperature of surface air, land and water; precipitation; evaporation; and wind patterns. It also affects aspects of the ocean system, including temperature, currents and sea level.
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.
Global climate change drives changes in regional climate. At the regional level, climate change can include:
- a change in average climate, such as average annual temperature;
- 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
- more frequent and/or 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 trigger severe and abrupt changes in regional climate.
Global Climate Change is Already Happening
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 the past 1,000 years.
- The global average temperature rose by 0.6°C over the 20th century.
- The 1990s was the warmest decade, and 1998 was the warmest year ever measured with instruments (since 1861).
- Snow cover has decreased by 10 per cent since the 1960s.
- Mountain glaciers in the non polar 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.
- The global average sea level rose between 10 to 20 centimetres over the past 100 years.
What causes climate change?
Human Influence on the Climate System
Fossil fuel burning has led to a significant increase in the amount of greenhouse gases (GHGs) 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 fuels. 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 GHGs 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, methane, nitrous oxide, sulphur hexafluoride, hydrofluorocarbons and perfluorocarbons. Scientists are able to lump these six gases together under the simple name "carbon" by figuring out their carbon dioxide equivalent. So when we talk about "carbon footprint" and "carbon neutral," for example, we are referring to all of the major greenhouse gases, not just carbon dioxide.
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 global average temperature will likely increase from 1.4°C to 5.6°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 northern latitudes (such as Canada) and the interior of continents (i.e., non coastal areas) — as much as 40 per cent greater than the global average.
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 climate change impacts, but they will not prevent climate change.
