Climate change,causes of climate change

Greenhouse Gases

Human activity has caused global warming by intensifying our atmosphere's natural heat-trapping potential.

Much like the glass of a greenhouse, gases in our atmosphere sustain life on earth by trapping the sun's heat. These gases allow the sun's rays to pass through and warm the earth, but prevent this warmth from escaping our atmosphere into space. Without naturally-occurring, heat-trapping gases - mainly water vapour, carbon dioxide and methane - Earth would be too cold to sustain life as we know it.

The danger lies in the rapid increase of carbon dioxide and other greenhouse gases that intensify this natural greenhouse effect. For thousands of years, the global carbon supply was essentially stable as natural processes removed as much carbon as they released. Modern human activity - burning fossil fuels, deforestation, intensive agriculture - has added huge quantities of carbon dioxide and other greenhouse gases.
Today's atmosphere contains 32 per cent more carbon dioxide than it did at the start of the industrial era. Levels of methane and carbon dioxide are the highest they have been in nearly half a million years.

Carbon dioxide is the most significant greenhouse gas. Here are some others:

Methane, released from cattle farming, waste dumps, rice farming and the production of oil and gas, has 21 times as much global warming potential as carbon dioxide.
Nitrous oxide, released by chemical fertilizers and burning fossil fuels, has a global warming potential 310 times that of carbon dioxide.
CFCs (chlorofluorocarbons), the notorious chemicals responsible for ozone holes, are also greenhouse gases

Climate is the prevailing weather of an area. Earth's atmosphere has gradually warmed and cooled over the millennia.Yet in the past 30 years, scientists have come to realize that fossil fuel combustion and ecosystem disruption have triggered more rapid climate change.

The 2,500 scientists of the subject's most authoritative body, the UN Intergovernmental Panel on Climate Change (IPCC), agree: "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activity." Since 1970, when the pace of climate change began to accelerate, the buildup of greenhouse gases has been to blame for more than two-thirds of the warming. Human activity is now clearly responsible for the majority of warming.

During the 20th century, the world's global average temperature increased by nearly one degree Celsius; nine of the ten hottest years on record have taken place in the 1990s. 1998 is thought to have been the millennium's warmest year, according to indicators such as tree rings and coral reefs, an astonishing half-degree warmer than the average for the last two decades. By 2050, if carbon dioxide concentration doubles from levels in the 1700s, average global temperature will rise 1.4 to 7.7 degrees Celsius (Nature (295) 113).

The effects of climate change are especially pronounced in Canada's north. In 1998, Canadian Arctic temperatures were five degrees Celsius above normal on average.
While warmer temperatures may sound appealing to some, climate change carries a potent threat - extremes of hot and cold weather, floods, drought, and destructive storms. Climate change endangers human health, and the health of our ecosystems. It jeopardizes agriculture, forestry, supplies of fresh water and the survival of some animal species.

Government and industry should be cautioned against exploiting provisions of the Kyoto Protocol related to forests and sinks as a way to avoid meeting commitments to reduce greenhouse gas emissions.

Although many projects, such as tree planting, may enhance carbon sinks and biodiversity, they could also diminish the impetus for long-term solutions to climate change: energy conservation and efficiency, and renewable energy sources. Unless fossil fuel use is reduced, air quality-related health impacts will also not be addressed.

See the David Suzuki Foundation report, Taking Credit, for more information about the science and policy of sinks.

Forests & Sinks

The natural greenhouse effect is being intensified as humans alter the global carbon cycle.

Forests, soil, oceans, the atmosphere, and fossil fuels are important stores of carbon. Carbon is constantly moving between these different stores, that act as either "sinks" or "sources." A sink absorbs more carbon than it gives off, while a source emits more than it absorbs. Before the Industrial Revolution, the amount of carbon moving between trees, soil, oceans and the atmosphere was relatively balanced.

Burning fossil fuels tips this balance. Oil, coal and gas combustion introduce at least 6 billion tonnes of carbon to the carbon cycle every year -- carbon that was stored underground, separated from the atmosphere for millions of years.
Living forests absorb carbon dioxide and, through photosynthesis, convert it to biomass. Forest soils also store large amounts of carbon in their organic layer. Deforestation alters the carbon cycle by eliminating trees and disturbing forest soils, releasing the carbon stored in both to the atmosphere.
Forest fires and decomposing wood waste and wood products also add significant amounts of carbon dioxide to the atmosphere. Until the 1980s, Canadian forests were a sink, according to the Canadian Forest Service. Through increased fires, insect infestation and harvesting, they have now become a net source.
Modern farming practices also disrupt the carbon cycle. Soils, which contain about 75 per cent of carbon found on land, are excellent sinks. Once cultivated, the amount of organic matter that soils contain drops by 20-50 per cent. Intensive farming, erosion and salinization accentuate the problem.

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