Earth's Climate
Climate is defined as average weather. A regions climate is its normal weather patterns and conditions. In contrast, weather refers to the state of the atmosphere at a given time in terms of temperature, rain, clouds, etc.
The climate system is made up of the atmosphere or air, the most characteristic component of climate, land surface, snow and ice, oceans and other water bodies and living things including plants, animals and microorganisms.
The climate system is powered by incoming solar radiation. Earth balances the Sun's incoming radiation through interactions between climate's 5 components. The Earth's radiation balance can be altered in 3 ways either directly or indirectly through feedback systems:
1. Changes in incoming shortwave solar radiation. The amount of incoming solar radiation changes as the Earth's moves. For example the amount of solar radiation reaching earth on an annual cycle as the Earth's orbit and tilt change causes the change in seasons. Changes to the Earth's movement also happens on longer time scales. The amount of incoming solar radiation also changes as the Sun cycles between high and low energy periods and is due to reach a maximum in 2012.
2. Changes in the amount of reflected solar radiation also called albedo. The amount of reflected radiation decreased when the ozone layer thinned and a hole developed because ozone reflects solar radiation in the upper atmosphere. Solar radiation is also reflected by snow and ice, clouds and aerosols. Aerosols are fine particles in the atmosphere.
3. Altering the amount of long wave radiation leaving Earth into space. Long wave radiation also know as thermal radiation or simply heat energy is given off by Earth to balance the incoming shortwave solar radiation. Greenhouse gases in the atmosphere absorb thermal radiation and send it back toward Earth.
Climate Change & Global Warming
Climate change is any change in normal weather patterns and is identified by statistical changes in weather over time based on weather records. Climate change occurs naturally, a past example are the ice ages. Recently, humans have contributed to climate change by adding greenhouse gases, aerosols, and increasing cloudiness in the atmosphere altering the Earth's radiation balance.
Global warming is the document increase in the Earth's near-surface air and ocean temperatures based on 157 years of worldwide temperature records. Global warming is a current example of climate change and is believed to be the result of changes in incoming solar radiation and greenhouse gases released by human activities. Since the beginning of the Industrial Era around 1750, human activities have had a warming effect that exceeds that due to natural processes.
Greenhouse Gases and the Greenhouse Effect
Greenhouse gases are gases that absorb and give off thermal radiation or simply heat energy. Greenhouse gases occur naturally in the environment and are also produced by human activities. The table below lists some major greenhouse gases and their sources.
The table above lists major greenhouse gases, if they are produce naturally or by human activities and their sources.
The Greenhouse Effect refers to how greenhouse gases heat the Earth's near-surface air and oceans. The Sun powers the Earth's climate system by constantly radiating energy at very short wave lengths (visible and ultraviolet light) toward Earth. About 1/3 of the energy that reaches Earth is reflected back into space by the upper atmosphere and the remaining energy is absorbed by the land surface and to a lesser extent the atmosphere.
To balance the incoming solar radiation, the Earth radiates about the same amount of energy back toward space as long wave, mainly infrared radiation or simply heat. Greenhouse gases in the atmosphere absorb most of the thermal radiation given off by Earth and then give the heat off back toward Earth, warming the near-surface air and oceans. This is the Greenhouse Effect and without it life as we know it would not be possible because the Earth's average temperature or, the average temperature for the entire planet, would be below the freezing point of water, around -18°C instead of its current average temperature of 15°C. An analogy for the Greenhouse Effect is like the glass in a greenhouse or car on a hot day. The glass lets sunlight in but does not let heat out warming the inside of the greenhouse.
The image above shows how the Greenhouse Effect works. The purple arrows illustrate short wave, ultraviolet radiation. The red arrows illustrate long wave, infrared radiation also know as heat. The gray area illustrates the atmosphere and some of the gases found within it are shown using their chemical symbols.
Humans have intensified the Greenhouse Effect by increasing the amount of greenhouse gases in the atmosphere primarily through fossil fuel burning and deforestation. The effects of this process are felt most in dry polar regions as opposed to wet equatorial regions because there is less water vapour, the most important greenhouse gas, in the atmosphere near the poles and therefore less of a natural greenhouse effect compared to equatorial regions.
Past Climate Change Compared to Current Climate Change
Climate change prior to the Industrial Era occurred as a result of changes in the Earth's radiation balance but the causes of the changes vary. For example glaciation. Past glaciation is thought to have occurred due to Milankovich Cycles that change the amount of solar radiation received at different latitudes through changes in Earth's orbit, axis and procession. Also, studies have shown that carbon dioxide concentrations in the atmosphere were lower during the glacial periods compared to interglacial periods. Changes in incoming solar radiation is another likely cause of past climate change.
Some aspects of the current climate change are not unusual but others are. The unusual aspects include the fact that the atmospheric carbon dioxide levels have reached record highs relative to the past half million years; the rate of change is more rapid than in the past, occurring over hundreds instead of thousands of years; past changes were attributed to natural causes and current changes to human activities; and, if the warming continues at the current rate the resulting change would be unusual on geologic terms. Click here to learn more about the potential impacts of global warming and climate change.
Carbon Dioxide Levels in the Atmosphere
Scientists have been monitoring the concentrations of greenhouse gases in the atmosphere at various locations around the globe. Results show that concentrations of greenhouse gases, particularly carbon dioxide, have increased. The graphs below show atmospheric carbon dioxide concentrations at the Mauna Loa Observatory in Hawaii over time.
The graph above shows recent monthly mean atmospheric carbon dioxide levels at the Mauna Loa Observatory Hawaii. The red line show monthly mean values. The black line shows the monthly mean values corrected for seasonal cycle. Carbon dioxide values vary seasonally because the majority of Earth's vegetation exists in the Northern Hemisphere and the carbon dioxide concentrations change with the annual growth cycle of plants. In the spring and summer, concentrations will decrease as plants start to grow, using carbon dioxide in photosynthesis and increase in the fall and winter as plants go dormant and no longer photosynthesize and dead organic matter decays. Graph produced by Dr. Pieter Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd.ccgg/trends) accessed 15 July 2010.
The Carbon Cycle
Humans have increased the amount of carbon dioxide in the atmosphere by burning fossil fuels and cutting down forests. These activities have disrupted the Earth's natural carbon cycle. Carbon in the environment does not stay still, it moves around between different sources, that release carbon, and sinks, that store carbon. In the atmosphere carbon is attached to two oxygen molecules to form a gas called carbon dioxide. Below is a brief description of the carbon cycle.
The image above is a simple illustration of the carbon cycle.
Carbon is stored in the oceans or on land in plants and soils and is released back to the atmosphere through decomposition of dead organic material and through the metabolism of organisms that produce carbon dioxide such as respiration. Carbon is also stored in rocks until they are exposed to the atmosphere and are broken down by chemical reactions. Also, the internal Earth stores carbon, releasing it during volcanic eruptions.
Oceans are the largest carbon sink. Carbon dioxide dissolves into the oceans and quickly undergoes a series of reactions that make the carbon available for use by marine organisms. Photosynthesizing marine organisms turn the carbon into carbohydrates and energy that gets passed up the food chain. Carbon is moved around the oceans, even the deep oceans, by the movement of organisms and their remains. Dead organisms may decompose releasing carbon back into the water where it may move to the surface and be released. Alternatively shells and other remains of organisms may get buried in sediments and get stored at the bottom of the ocean for millions of years. Overtime the heat and pressure from being buried will turn the organic remains into fossils fuels such as coal or oil. Carbon storage through the process of sedimentation happens at a very slow rate, slower than the rate at which humans are releasing carbon into the atmosphere by burning fossil fuels bringing previously stored carbon back into the atmosphere sooner than would have occurred naturally. But even though the oceans are the largest sink, they have limited capacity to absorb carbon dioxide and the capacity is currently shrinking because of the amount of carbon dioxide produced by human activities. As the oceans warm with global warming the amount of carbon dioxide that can dissolve into the oceans decreases. The oceans capacity to absorb carbon dioxide is further decreased by the oceans becoming more acidic from the higher amount of carbon dioxide currently dissolving into the oceans, a process called ocean acidification.
On land photosynthesizing organisms such as plants, absorb carbon dioxide and use it to make carbohydrates and energy to live and grow, storing carbon in plant matter which can move up the food chain. The carbon stored in plants or other organisms is released during the decomposition of dead organisms or through an organisms metabolism that released carbon such as respiration. Carbon can be released from forests and grasslands by wildfires and wood harvesting. Although a wooden desk may be used for many years, storing carbon its whole lifetime, the processing of the wood from being cut to made into a desk releases carbon at a number of steps along the way. On land carbon can also be stored in wetlands as peat for longer periods of time than in plants and animals. However, as temperatures rise and the climate dries, the organic matter making up the peat will start to decompose and will release carbon as carbon dioxide and methane turning these carbon sink into sources. Melting of permafrost is another source of carbon, the organic matter stored in frozen soils will start to decompose when they thaw releasing carbon dioxide and methane to the atmosphere.
Reference: IPCC, 2007: Climate Change 2007: The Physical Science Bases. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
Go Green Home Get Involved How to Go Green Climate Change Impacts
Carbon Budget Calculator Matawa Home
