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Climate Change

Changes in our climate, globally and locally, are a result of an increase in heat-trapping, greenhouse gases (GHG) in air directly above the Earth’s surface. In particular, most climate scientists agree the main cause of global warming is human expansion of the greenhouse gas effect.
Many greenhouse gases occur naturally and are necessary for life, but the additional gases generated by human activities are thought to be a major catalyst for changes in the Earth’s climate.
These greenhouse gases cause the Earth’s temperature to rise because they prevent heat from escaping the surface. Global temperatures have risen sharply over the past 200 years; the most notable increase occurred in the last 50 years.
Efforts locally, statewide and nationally are under way to reduce greenhouse gas emissions. Even so, the public and private sector need to continue to work together to make others aware of how they can help encourage changes in behavior or policies to ensure our air remains healthy for everyone.

Greenhouse Gas Sources and Trends

Naturally occurring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide and ozone. In addition, some human activities, such as electricity and natural gas consumption, vehicle travel, manufacturing and agricultural practices also produce greenhouse gases.

Greenhouse gases cause the Earth’s temperature to rise because they prevent heat from escaping the surface. This warming effect leads to changes in our climate which can disrupt rainfall, snow and/or wind patterns and alter the distribution andabundance of plants and animals. Natural factors such as the Earth’s orbital variations or ocean circulation can contribute to climate change but many human activities also contribute to the planet’s warming trends.

Scientists predict that if humans continue to emit greenhouse gases at the current rate, the average global temperature will rise by 3 to 7degrees Fahrenheit (F) by 2100 (Intergovernmental Panel on Climate Change, 2007). Impacts in the Southwest U.S. are predicted to be more severe.

Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the major human caused greenhouse gases and below is a summary of each.

National and Local Trends

In its most recent inventory, the U.S. Environmental Protection Agency reported that U.S. greenhouse gas emissions rose by 8 percent from 1990 to 2011 (EPA, 2013), with a 5 percent decline from 2008 to 2011 period. In 2011, 65 percent of total U.S. greenhouse gas emissions were attributed to residential, commercial and industrial energy use and 33 percent was generated by the transportation sector.

Regional trends in greenhouse gas emissions mirror those of the nation. In the Tucson region, greenhouse gas emissions rose by 41 percent from 1990-2010, with a slight drop in emissions from 2008 to 2010. Residential, commercial and industrial energy use was responsible for two-thirds of the 2010 greenhouse gas emissions total, with transportation emissions contributing about one-third to the annual total.


Local Impacts

Mitigation and Adaptation Strategies

Mitigation refers to actions taken to reduce greenhouse gas emissions. Adaptation refers to minimizing the risks and hazards of climate change. Pima Association of Governments along with the various jurisdictions have programs that help to reduce greenhouse gas emissions and promote adaptation strategies buffering the damaging effects of regional climate change.

Pima Association of Governments

Pima County

City of Tucson


Oro Valley




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