The climate system
What is climate?
The main elements of the climate system include the Sun (source of heat energy), atmosphere (providing a protective blanket), oceans (helping to distribute heat through its currents), water (as rain, snow, or ice), and land (reflecting or absorbing energy from the Sun). Changes to any of these elements affect the balance of the entire system.
Climate has always changed
Earth's climate is naturally variable. Warming and cooling trends are part of normal climatic cycles. Climatic conditions vary within a single year, from one year to the next, and over decades, centuries, and millennia. Historically, there have been frequent changes in climate, with repeated fluctuations between colder and warmer conditions.
Ice age glacier 900 meters thick
Past changes in climate have been sufficient to cause major shifts in global ecosystems, with significant impacts on natural habitat and human development. At the peak of the last Ice Age (about 20 000 years ago), what is now Toronto was buried under about 900 metres of ice!
Balancing the budgets
The solar energy budget
Of the total amount of radiation received from the Sun, roughly one third is reflected back into space by clouds and the Earth's surface. The remainder is absorbed by the Earth and its atmosphere. Some of this heat is radiated back into space, but most of it is trapped by our atmosphere, which acts like a large insulating blanket. The 'greenhouse effect' refers to the heat-trapping quality of the atmosphere created by gases known as 'greenhouse gases'.
Without this insulation, Earth would be about 33°C colder than it is now, making it inhospitable to life. When the amounts of these gases change, the capacity of the atmosphere to trap heat also changes.
Infrared radiation emitted by the Earths surface
The carbon balance
Carbon is naturally present in the atmosphere (as CO2) and in the oceans. Huge amounts of carbon are also stored within the Earth in fossil fuels and sedimentary rock, vegetation and soils. Before the Industrial Revolution, additions of CO2 and other greenhouse gases to the atmosphere were largely balanced by removals by the oceans and vegetation.
Greenhouse gases: the big three
The main greenhouse gases are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Methane and nitrous oxide are much more potent greenhouse gases, but CO2 is much more abundant.
Climate or weather?
Although the terms are commonly used interchangeably, there is an important distinction between 'weather' and 'climate'. The term 'weather' describes the day-to-day and hour-by-hour changes in atmospheric conditions at a given location. 'Climate' describes the synthesis of these day-to-day variations into a set of average or expected conditions. Traditionally, it has been assumed that the climate we have experienced in recent history will be the climate we will experience in the future. Many of the decisions we make as a society depend on this assumption.
Did you know?
Although instrumental temperature records only date back about 150 years, scientists can establish temperatures back tens of thousands of years by analyzing the gases found in ice cores from the Arctic and Antarctic.
References
Mann, M.E., Bradley, R.C., and Hughes, M.K., 1999: Northern hemisphere temperature during the past millenium: inferences, uncertainties, and limitations; in Geophysical Research Letters, V. 26, no.6, p. 759-762.
Government of Canada, 1999: Canada's Perspective on Climate Change: Science, Impacts and Adaptation (online; http://www.ec.gc.ca/cc/CoP5/SIA/english/index.htm).
Folland, C.K., Karl, T.R., and Vinnikov, K., 1990: Observed climate variations and change; in Climate Change: the IPCC (Intergovernmental Panel on Climate Change) Scientific Assessment, Cambridge University Press, London, United Kingdom, p. 195-238.
Environment Canada, 1993: A matter of degrees: a primer on global warming; The Environmental Citizenship Series, Environment Canada, Ottawa, Ontario, 89 p.