Greenhouse Gases

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Greenhouse gases are gases that absorb energy emitted from the earth and radiate it back into the atmosphere.  If there are too many greenhouse gases, the earth could become too warm. If greenhouse gases dramatically decrease, the earth may be too cool for human activities, such as farming, planting, and harvesting, to occur.

Why do I care? A certain amount of greenhouse gases  is essential to life on earth.  However, human activities are affecting the levels of these gases in the atmosphere, which are in turn affecting the climate we have adapted to.

I should already be familiar with: Greenhouse Effect

How a greenhouse gas works
Figure A. Carbon dioxide, a greenhouse gas which absorbs and emits infrared radiation

Greenhouse gases are the gases that absorb long-wave energy and emit it back into our atmosphere.  They are responsible for keeping the earth warm enough to live on.  Most of these gases are present in the atmosphere naturally.  However, anthropogenic (manmade) processes are dramatically increasing the concentration of these gases.  This is one of the main reasons we think our earth is experiencing warming and climate changes. 

Concentrations of greenhouse gases are commonly given in percentages as well as mixing ratios of gases to total air volume, such as ppt, ppb, and ppm.  The percentages are the percentage of the atmosphere made up by these gases.  Since the percentages are very small, most of the time concentrations are referred to in parts per trillion (ppt), parts per billion (ppb) or parts per million (ppm).  This means that for every trillion, billion or million molecules, the number given is the amount of molecules that are composed of that gas per trillion air molecules, etc.  For example, as of 2009, our atmosphere currently contains a CO2 concentration of 385ppm; for every million molecules, about 385 of them are carbon dioxide. 

In the linked pages, you should also keep in mind that a fossil fuel is any hydrogen and carbon rich substance that was created by the decomposition of prehistoric plants and animals that can be burned to produce heat or energy.  This includes coal, petroleum, and natural gas products.

Below is a video from the National Academies of Science of how greenhouse gas concentrations have changed over the last century.


How does this relate to public health?

Figure B. Greenhouse gases. (Image from EPA).

Greenhouse gases are contributing to global warming and climate change by causing increased temperatures. Warmer temperatures may lead to increased frequency and severity of heat-related illnesses and reduced water and air quality, which in turn have a variety of adverse effects on human health. These include increased risk for cancer, foodborne and waterborne illnesses, cardiovascular and respiratory diseases, vectorborne and zoonotic diseases, mental health and stress-related illnesses, and human developmental effects.1

1Portier CJ, et al. 2010. A human health perspective on climate change: a report outlining the research needs on the human health effects of climate change. Research Triangle Park, NC: Environmental Health Perspectives/National Institute of Environmental Health Sciences. doi:10.1289/ehp.1002272 <> Accessed November 17, 2012.


Want to learn more?

Carbon DioxideMethaneNitrous OxideOzoneWater VaporHalocarbonsOzone Layer


Links to National Science Education Standards:

Earth Science: EEn.2.6.2 : Explain changes in global climate due to natural processes.


Activities to accompany the information above:

Activity: Ground-level Ozone: Your Vehicle (pdf version of original activity.)

Description: This activity will assist students in understanding the role of vehicles on greenhouse gas levels. Students will use their vehicle or their parent's vehicle to calculate the emissions levels for nitrogen oxides and hydrocarbons and compare the values to a hybrid vehicle. This activity is focused more toward an AP Environmental Science class.

Relationships to topics: Greenhouse GasesOzone LayerCauses of Climate Change


Activity: Human Activity and Climate Change  (Link to original activity.)

Description: This activity focuses on the increase in greenhouse gas emissions associated with human activity. Students will observe changes in greenhouse gases through graphs and will also calculate their contribution to greenhouse gas levels. This activity can be used in an AP Environmental Science class or an advanced Earth Science class.

Relationships to topicsGreenhouse Gases


Activity: Trees and Carbon (pdf version of original activity.)

Description: This activity will assist students in understanding the importance of forests on the carbon dioxide level and the amount of carbon that the trees are able to store. Useful mainly for an AP Environmental Science class.

Relationships to topics: Greenhouse EffectGreenhouse GasesGlobal Warming vs. Climate Change


Activity: What is a Greenhouse?  (Link to original activity.)

Description: This activity focuses on how a greenhouse retains heat. Students will build a greenhouse model to explain this process.

Relationships to topicsLongwave & Shortwave RadiationGreenhouse EffectGreenhouse GasesOzone,  Nitrous OxideCarbon DioxideMethaneWater VaporHalocarbons