The Causes of Global Warming

Global warming is caused by excessive quantities of greenhouse gases emitted into Earth's near-surface atmosphere. Greenhouse gases are both man-made and occur naturally, and include a number of gases, including:

• carbon dioxide
• methane
• nitrous oxide
• chlorofluorocarbons
• water vapor

Optimal amounts of naturally occurring greenhouse gases, especially water vapor, are necessary to maintain the Earth's temperature at inhabitable levels. Without greenhouse gases, Earth's temperature would be too cold for human and most other life.

However, excessive greenhouse gases cause Earth's temperature to warm considerably which cause major, and occasionally catastrophic, changes to weather and wind patterns, and the severity and frequency of various types of storms.

For more, read President Obama's Speech at U.N. Climate Change Conference in Copenhagen.

Greenhouse Gases Generated by Mankind

The scientific community as a whole has concluded that naturally occurring greenhouse gases have remained fairly constant over the past several hundred years.

Greenhouse gases directly and indirectly generated by mankind, though, have increased radically for the past 150 years, and especially in the past 60 years.

Major sources of greenhouse gases generated by mankind are:

• Burning of fossil fuels, which includes oil and gas, coal and natural gas.
• Chlorofluorocarbons, commonly used in refrigeration, cooling and manufacturing applications.
• Methane, which is caused by emissions from landfills, livestock, rice farming (which uses methane-emitting bacteria), septic processes, and fertilizers.
• Deforestation

Per Rainforests.com, "The largest (manmade)contributor to the greenhouse effect is carbon dioxide gas emissions, about 77 percent of which comes from the combustion of fossil fuels and 22 percent of which is attributed to deforestation."

Vehicles Burning Fossil Fuels Are Primary Source

The largest single contributer to the rise of man-made greenhouse gases is, of course, the burning of oil and gas to power vehicles, machinery, and produce energy and warmth.

The Union of Concerned Scientists observed in 2005:

"Motor vehicles are responsible for almost a quarter of annual U.S. emissions of carbon dioxide (CO2), the primary global-warming gas. The U.S. transportation sector emits more CO2 than all but three other countries' emissions from all sources combined. And motor vehicle emissions will continue to increase as more vehicles hit America's roads and the number of miles driven grows.

"Three factors contribute to CO2 emissions from cars and trucks:

• Amount of fuel used
• Amount of CO2 released when a particular fuel is consumed
• Number of vehicle miles traveled."

Deforestation Is Also Major Source

But deforestation is also an important, if lesser known, culprit for causing greenhouse gas emissions. The United Nations Food & Agriculture Organization (FAO) observed in 2006:

"Most people assume that global warming is caused by burning oil and gas. But in fact between 25 and 30 percent of the greenhouse gases released into the atmosphere each year – 1.6 billion tonnes – is caused by deforestation...

"Trees are 50 percent carbon. When they are felled or burned, the C02 they store escapes back into the air... Deforestation remains high in Africa, Latin America and Southeast Asia."

And the situation is worsening, per Science News Daily, which wrote in late 2008, "Decreasing forest cover, almost exclusively from deforestation in tropical countries, was responsible for an estimated 1.5 billion tons of emissions to the atmosphere above what was gained through new plantings."

Summary of "Causes of Global Warming"

Global warmming is cuased by greenhouse gases, which occur both naturally and are directly and indirectly generated by mankind.

While optimal amounts of greenhouse gases are necessary for Earth to be habitable, a profusion of greenhouse gases create disturbances in weather and storm patterns that can be catastropic.

Man-made greenhouse gases have increased greatly in the last 50 years. Among the largest sources of man-made gases are fossil-fuel burning vehicles, worldwide deforestation, and sources of methane such as sandfills, septic systems, livestock, and fertilizers.

See other quick-reading articles in this series:

• What Is Global Warming?
• Global Warming Facts and Evidence
• The Effects of Global Warming
• Solutions to Stop or Slow Global Warming

Also read President Obama's Speech at U.N. Climate Change Conference in Copenhagen.

For in-depth info on global warming causes, see Global Warming: Causes, Effects and Solutions by Larry West, About.com Guide to Environmental Issues.