Gases that trap heat in the atmosphere are often called greenhouse gases. Some greenhouse gases such as carbon dioxide occur naturally and are emitted to the atmosphere both through natural processes and human activities. Other greenhouse gases (such as fluorinated gases) are created and emitted solely through human activities. The following are the principal greenhouse gases that enter the atmosphere because of human activities:

• Carbon dioxide (CO₂)
• Methane (CH₄)
• Nitrous oxide (N₂O)
• Fluorinated gases

Climate change affects people, plants, and animals. Observed effects include sea level rise, shrinking glaciers, changes in the range and distribution of plants and animals, earlier-blooming trees, longer growing seasons, late freezes and early thaws of ice on rivers and lakes, and thawing of permafrost. Human health can be affected directly and indirectly by climate change in part through extreme periods of heat and cold, storms, increase in climate-sensitive diseases, and smog episodes. Specifically, local governments may be faced with challenges such as the following:

• Considering development of land in flood-risk areas
• Ensuring building standards are adequate to withstand changes in weather events
• Weighing the adequacy of emergency procedures
• Addressing public health and welfare effects from uncharacteristic events triggered by climate change

Local governments can directly effect change through policy or program decisions.

Reducing greenhouse gas emissions has many other benefits. These include saving money, creating jobs, promoting sustainable growth, and reducing air pollution.