Global climate change refers to the change in the long-term weather patterns that characterize the regions of the world. The term "weather" refers to the short-term (daily) changes in temperature, wind, and/or precipitation of a region. Weather is influenced by the sun. The sun heats the earth's atmosphere and its surface causing air and water to move around the planet. The result can be as simple as a slight breeze or as complex as the formation of a tornado.

Some of the sun's incoming long wave radiation is reflected back to space by aerosols. Aerosols are very small particles of dust, water vapor, and chemicals in Earth's atmosphere. In addition, some of the sun's energy that has entered Earth's atmosphere is reflected into space by the planet's surface. The reflectivity of Earth's surface is called albedo. Both of these reflective processes have a cooling effect on the planet.

The greenhouse effect is a warming process that balances Earth's cooling processes. During this process, sunlight passes through Earth's atmosphere as short-wave radiation. Some of the radiation is absorbed by the planet's surface. As Earth's surface is heated, it emits long wave radiation toward the atmosphere. In the atmosphere, some of the long wave radiation is absorbed by certain gases called greenhouse gases. Greenhouse gases include carbon dioxide (CO2), Chlorofluorocarbons (CFCs), methane (CH4), nitrous oxide (N2O), tropospheric ozone (O3), and water vapor. Each molecule of greenhouse gas becomes energized by the long wave radiation. The energized molecules of gas then emit heat energy in all directions. By emitting heat energy toward Earth, greenhouse gases increase Earth's temperature. Note that the warning mechanism for the "greenhouse effect" is NOT exactly the same as the warning mechanism of greenhouse walls. While greenhouse gases absorb long wave radiation then emit heat energy in all directions, greenhouse walls physically trap heat inside of greenhouses and prevent it from escaping to the atmosphere.

The greenhouse effect is a natural occurrence that maintains Earth's average temperature at approximately 60 degrees Fahrenheit. The greenhouse effect is a necessary phenomenon that keeps all Earth's heat from escaping to the outer atmosphere. Without the greenhouse effect, temperatures on Earth would be much lower than they are now, and the existence of life on this planet would not be possible. However, too many greenhouse gases in Earth's atmosphere could increase the greenhouse effect. This could result in an increase in mean global temperatures as well as changes in precipitation patterns.

When weather patterns for an area change in one direction over long periods of time, they can result in a net climate change for that area. The key concept in climate change is time. Natural changes in climate usually occur over; that is to say they occur over such long periods of time that they are often not noticed within several human lifetimes. This gradual nature of the changes in climate enables the plants, animals, and microorganisms on earth to evolve and adapt to the new temperatures, precipitation patterns, etc.

The real threat of climate change lies in how rapidly the change occurs. For example, over the past 130 years, the 7 mean global temperature appears to have risen 0.6 to 1.2 degrees Fahrenheit (0.3 to 0.7 degrees Celsius). Further evidence suggests that future increases in mean global temperature may occur at a rate of 0.4 degrees Fahrenheit (0.2 degrees Celsius) each decade.

The geological record provides evidence of climate changes similar in magnitude to those statistics. This means during the history of the earth, there have been changes in global temperatures similar in size to these changes. However, the past changes occurred at much slower rates, and thus they were spread out over long periods of time. The slow rate of change allowed most species enough time to adapt to the new climate. The current and predicted rates of temperature change, on the other hand, may be harmful to ecosystems. This is because these rates of temperature change are much faster than those of Earth's past. Many species of plants, animals, and microorganisms may not have enough time to adapt to the new climate. These organisms may become extinct.

Human Influences

In his book "Biogeochemistry: An Analysis of Global Change," William Schlesinger states, "Humans affect the global system by creating a large biogeochemical flux where none existed before". This means that while nature has its own way of keeping all of its systems in balance, human activities have created an imbalance — a flux — among the systems. One such imbalance that our species may be causing is in the earth's climate. Many human activities produce gases that contribute to the greenhouse effect, a process that warms the earth's atmosphere. The gases that contribute to this effect are called greenhouse gases. At natural concentrations, greenhouse gases benefit the planet by maintaining temperatures required for life. However, human activities are increasing the concentrations of these gases in the atmosphere. This is increasing the greenhouse effect and thus increasing the global temperature of the planet. Major greenhouse gases include chlorofluorocarbons (CFCs), methane (CH4), nitrous oxide (N2O), and tropospheric ozone (O3). The biggest influence humans have on the greenhouse effect is the production of carbon dioxide (CO2). This is a very powerful greenhouse gas that comes from many human activities.

Impacts

Climate affects everything from the flora and fauna which inhabit a region to the heating and cooling requirements of homes and businesses. When climate begins to change, all living things must adapt their lifestyles in order to survive. Global climate change could impact agriculture, ecosystems, forests, sea level, regional weather, human health, and human economics.

Agriculture

Changes in temperature and precipitation patterns may lead to changes in the length of growing seasons and/or the rates of photosynthesis by plants. Such changes could lead to decrease in crop yield.

A major cause of global climate change — increased concentrations of atmospheric carbon dioxide (CO2) — may actually cause some plants to grow better.

Ecosystems

Biomes, which are closely related to the temperature and precipitation of a region, may actually change. For example, some forest regions could warm up, dry out, and become deserts. Warmer temperatures in northern latitudes may cause alpine forests to disappear as temperate forests migrate northward into these areas that had previously been too cold for them to survive.

Since ecosystem evolution is generally a slow process, some elements of an ecosystem might have problems adapting to rapid climate change and may not survive. For example, increased ocean temperatures may cause a decline in fisheries.

Sea Level

If increased temperatures cause the polar ice sheets to melt, then sea level will rise as a result of the increased amount of water flowing into the sea.