Sierra Club of Canada Fact Sheet

Climate Change

People are changing the world's climate system

The earth's climate system is driven by energy from the sun and regulated by naturally occurring trace gases like carbon dioxide (CO2), methane (CH4) and nitrous oxide (N20) that make up less than 1 per cent of the atmosphere. (1 )

Here's how it works...

About half of the incoming solar radiation from the sun makes it to the earth's surface where it is absorbed and turned into heat energy. This heat energy is re-radiated from the earth's surface as long-wave radiation. Greenhouse gases like water vapour, carbon dioxide, methane and nitrous oxide trap this heat energy and send it back to earth. This process of counterradiation is what makes the earth's surface warm enough for life to survive. Over time, even this energy is reflected out to space. There is an equilibrium - the energy coming into the system is balanced by the energy leaving the system. (2 ) At least that was the story until human activity upset the balance.

People are "enhancing" the natural greenhouse effect

Carbon dioxide, methane and nitrous oxide are also released into the air when people burn coal, gasoline and natural gas for energy, and when forests are cut and burned for urban development, agriculture and wood products. These "extra" greenhouse gases mean that more heat is being trapped in the atmosphere. More heat means more evaporation and that means more water vapour - the most abundant greenhouse gas - and that means more warming.

In 1994, approximately 7 billion tonnes of carbon from burning fossil fuels and deforestation were released globally. About half of this carbon is taken up by natural processes; (3 ) the other half remains in the atmosphere for 50 - 200 years. That means each year some 3.5 billion tonnes of carbon are added to the totals released years before, increasing global concentrations of carbon in the atmosphere.

So far, concentrations have increased from pre-industrial levels of 280 parts per million by volume (ppmv) to 360 ppmv today. (4 ) Other greenhouse gases are destroyed over time by atmospheric chemistry - a process that can take decades to centuries.

These extra greenhouse gases are changing the world's climate.

Adding more greenhouse gases to the atmosphere than can be disposed of naturally is like adding an extra blanket to your bed: things are going to heat up. According to climate scientists, this extra heat energy in the atmosphere will increase global average surface temperatures between 1 - 3.500C by 2100 and increase climate instability. Averages, however, don't tell the whole story; climate change is a tale of extremes.

Countries in higher latitudes, like Canada, will see temperature increases much higher than global averages suggest. Some models predict, for example, increases of up to 80C for the Arctic.

Climate change is far away, what about today's problems?

According to the IPCC's 1995 Scientific Assessment, climate change has already started. The consensus view of the scientific community is that "the balance of evidence suggests a discernable human influence on global climate."

This conclusion is based on the following observations:

1. "Global mean surface temperature has increased by between 0.3 and 0.60C since the late 19th century (1.10C in Canada). 1995 was the warmest year on record; the 11 warmest years on record have all occurred since 1980."

2. "Recent years have been among the warmest since 1860, i.e., in the period of instrumental record, despite the cooling effect of the 1991 Mt. Pinatubo volcanic eruption."

3. "Night-time temperatures over land have generally increased more than daytime temperatures."

4. "Regional changes are also evident. For example, the recent warming has been greatest over the mid-latitude continents in winter and spring (Canada), with a few areas of cooling, such as the North Atlantic ocean. Precipitation has increased over land in high latitudes of the Northern Hemisphere, especially during the cold season."

5. "Global sea level has risen between 10 and 25 cm over the past 100 years and much of the rise may be related to the increase in global temperature."

6. "The 1990 to mid-1995 persistent warm-phase of the El Nino-Southern Oscillation (which causes droughts and floods in many regions) was unusual in the context of the last 120 years."

This is what the IPCC says could happen:

1. Temperature increase: 1 to 3.50oC increase in global mean surface temperature by 2100, with 20C considered a 'best guess'. It is the rate of warming that has scientists particularly concerned. "In all cases, the average rate of warming would probably be greater than any seen in the last 10,000 years, but the actual annual to decadal changes would include considerable natural variability. Because of the thermal inertia of the oceans (oceans absorb heat over long timescales), temperature would continue to increase beyond 2100, even if concentrations of greenhouse gases were stabilized by that time."

Warming would not be distributed evenly around the world. There will be "...greater surface warming of the land than the sea in winter; a maximum surface warming in high northern latitudes in winter, little surface warming over the Arctic in summer; an enhanced global mean hydrological cycle (for every degree increase in temperature, precipitation globally is expected to increase 2.5 per cent), and increased precipitation and soil moisture in high latitudes in winter. All these changes are associated with identifiable physical mechanisms."

Expect more heat waves: "A general warming tends to lead to an increase in extremely hot days and a decrease in the occurrence of extremely cold days.

These temperature increases will set in motion changes to every aspect of the earth's environment, including:

2. Projected sea level rise: 15 cm to 95 cm by 2100, with a 'best guess' of 50 cm.. "Sea level would continue to rise at a similar rate in future centuries beyond 2100, even if concentrations of greenhouse gases were stabilized by that time." Changes in air circulation, water temperatures and precipitation (which will change the density of salt water) also will change ocean circulation patterns affecting fish species distribution.

3. Changing precipitation patterns: "Warmer temperatures will lead to a more vigorous hydrological cycle; this translates into prospects for more severe droughts and/or floods in some places and less severe droughts and/or floods in other places. Several models indicate an increase in precipitation intensity, suggesting a possibility for more extreme rainfall events. Knowledge is currently insufficient to say whether there will be any changes in the occurrence or geographical distribution of severe storms, e.g. tropical cyclones."

4. The temperature difference between daytime highs and nighttime lows (diurnal range) is expected to decrease.

Fossil fuels give us more than just climate change

Burning fossil fuels contributes to other air pollution problems like acid rain and smog that also damage forests, lakes and agricultural crops. The biggest impact from these pollutants, however, may be on human health. Emissions from burning energy include tiny particles which we breath deep into our lungs. Once there, these pollutants cause respiratory problems like asthma and bronchitis, and cardiac problems. If these particles carry toxics like benzene, furans or dioxins, they can eventually cause cancer.

These particles also intercept and reflect solar radiation - they have a cooling effect on the atmosphere in those areas where they are emitted. This does not mean that climate change is not real. In fact, it makes things worse. These aerosols are masking serious increases in temperature. As we move to reduce these emissions for environment and health reasons, the result will be an unmasking of this hidden climate change.


1 Climate refers to the average over time of individual weather elements like rain, cloud cover, wind and temperature. Day-to-day variations are weather.

2 This simplified version of the natural and enhanced greenhouse effect is based on: Radiative Forcing of Climate Change, The 1994 Report of the Scientific Assessment Working Group of the IPCC. Also: A Matter of Degrees: a Primer on Global Warming, Environment Canada

3 Carbon dioxide and methane mostly come from energy, but methane is also emitted from landfills, manure and livestock; nitrous oxide is released from cars, fertilizers and nylon production.

4 All living plants, including trees, absorb carbon dioxide from the atmosphere while they are growing through a chemical process call photosynthesis (The sun's light energy is used by chlorophyll to capture carbon dioxide and water which is then converted to sugars, and then carbohydrates and cellulose to make the plant's body.). When trees and plants die, or are burned, they release this carbon dioxide back into the atmosphere. This stored carbon is called a reservoir because it remains stored only for the life of the plant or tree. Under normal conditions, growing plants (including phytoplankton in the oceans) absorbing carbon dioxide are in balance with carbon dioxide released into the atmosphere from burning and decomposing plants.


Copyright 1996 Sierra Club of Canada