Forests, soils, oceans, and the atmosphere are important stores of carbon, and before the Industrial Revolution, the amount of carbon moving between these stores was relatively balanced.
Yet humans have tipped the balance and altered the global carbon cycle, primarily by releasing vast amounts of carbon through the burning of fossil fuels. Oil, coal and gas combustion introduced 8.5 billion tonnes of carbon to the carbon cycle in 2007 —carbon that was until then stored underground for millions of years, and away from the atmosphere.
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Carbon stores act as either "sinks" or "sources". A sink absorbs more carbon than it gives off, while a source emits more than it absorbs. Until recently, Canadian forests were a sink, according to the Canadian Forest Service. 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. Through increased fires, insect infestation and harvesting, Canadian forests have now become a net source of greenhouse gas emissions. Global warming is expected to exacerbate the problem by increasing the likelihood of forest fires and insect infestations, such as the mountain pine beetle.
Modern farming practices also disrupt the carbon cycle. Soils, which contain about 75 per cent of carbon found on land, are excellent sinks. However, intensive farming, synthetic fertilizer use, soil erosion and salinization all reduce the amount of organic matter that soils contain.
Government and industry should be cautioned against exploiting provisions of the Kyoto Protocol related to forests and other 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. This is because they do not target the source of the emissions, which will continue to rise without additional measures.