The "greenhouse effect" is a natural phenomenon in which heat-trapping gases in the atmosphere, primarily carbon dioxide and water vapor, keep the Earth’s surface warm. It is named this way because of a similar effect produced by the glass panes of a greenhouse.

Solar radiation from the sun passes through Earth's atmosphere, then is absorbed by the surface of the Earth, causing it to warm. Part of the absorbed energy is then radiated back into the atmosphere as infared radiation. Greenhouse gases selectively transmit the infared waves, allowing some to pass through into space and trapping others within the lower atmosphere causing it to become warmer.

Source: Modified from Climate Literacy: The Essential Principles of Climate -March 2009 U.S Climate Change Science Program

Human activities, primarily burning fossil fuels and changing land cover patterns, are increasing the concentrations of some of these greenhouse gases, thereby amplifying the natural greenhouse effect and causing increased warming of the atmosphere.

By driving cars, using electricity from coal-fired power plants, or heating our homes with oil or natural gas, we release carbon dioxide and other heat-trapping gases into the atmosphere. Deforestation is another significant source of greenhouse gases, because fewer trees means less carbon dioxide is converted into woody biomass and oxygen.

Human activities are impacting the climate system

The overwhelming consensus of scientific studies on climate indicates that most of the observed increase in global average temperatures since the latter part of the 20th century is very likely due to human activities, primarily from increases in greenhouse gas concentrations resulting from the burning of fossil fuels.

Emissions from the widespread burning of fossil fuels since the start of the Industrial Revolution have increased the concentration of greenhouse gases in the atmosphere. Because these gases can remain in the atmosphere for hundreds of years before being removed by natural processes, their warming influence is projected to persist into the next century.

Growing evidence shows that changes in many physical and biological systems are linked to human- caused global warming. Some changes resulting from human activities have decreased the capacity of the environment to support various species and have substantially reduced ecosystem biodiversity and ecological resilience.

Human activities have affected the land, oceans, and atmosphere, and these changes have altered global climate patterns. Burning fossil fuels, releasing chemicals into the atmosphere, reducing the amount of forest cover, and rapid expansion of farming, development, and industrial activities are releasing carbon dioxide into the atmosphere and changing the balance of the climate system.

Scientists and economists predict that there will be both positive and negative impacts from global climate change. If warming exceeds 2 to 3°C (3.6 to 5.4°F) over the next century, the consequences of the negative impacts are likely to be much greater than the consequences of the positive impacts.

Source: Modified from Climate Literacy: The Essential Principles of Climate -March 2009 U.S Climate Change Science Program

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