Large carbon footprints don't always equal large quantities of blissful happiness.

­AP Photo/Eugene Hoshiko

Bad air quality days may be becoming more common than bad hair days. Greenhouse gases including carbon dioxide (CO2), methane, nitrous oxide and fluorinated gases have been increasing in the Earth's atmosphere at an alarming rate since the industrial revolution. It's these gases that contribute to the code red days reported on the local news in the United States. CO2 emissions alone (those caused by burning fossil fuels) increased by a stunning 20 percent from 1990 to 2004 [source: Environmental Protection Agency].

Greenhouse gases are linked to climate change. The accelerated rate of climate change can already be observed around us, causing rising sea levels, stronger storms and more extreme temperatures, as well as disappearing glaciers and the loss of ecosystems. It's not only the planet that suffers from the effects of these greenhouse gases, though. If climate change keeps trending this way, scientists predict extreme weather coupled with increased smog from air pollution will leave humans more susceptible to heart disease, respiratory illnesses such as asthma, as well as disease outbreaks and untimely death. A global temperature increase of about 2 degrees F (1 degree C) translates into roughly 1,000 more deaths each year in the United States and 20,000 air pollution-related deaths around the world [source: ScienceDaily].

­However, it's not only our bodies we should be concerned about, but our happiness, too: Carbon emissions may be putting it at risk. A correlation between happiness and carbon emissions? Perhaps so.

­Philosophers and social scientists have been thinking about happiness and how to define it for ages. Happiness itself is subjective -- what makes you happy may or may not make someone else so. Studies measuring happiness, including the World Database of Happiness project, rely on subjective data rather than objective data, and generally define happiness as how satisfied a person is with the quality of his or her life. What causes us to be happy or unhappy greatly varies from person to person and among cultures -- Americans, for example, often find happiness through retail therapy. Recently, the New Economics Foundation (NEF), a think tank, developed a formula for measuring how human happiness doesn't have to come with energy consumption and social inequality as its price tag.