Which countries are the worst emitters of carbon dioxide?

Researchers continue to develop the best metrics for ranking polluting countries, and now, a new factor has come into play.

In a new study, University of Michigan researchers accounted for both climate and GDP when looking at total emissions from each country. The addition of climate considerations led to surprising results, researchers Michael Sivak and Brandon Schoettle recently explained in American Scientist.

Sivak, director of Sustainable Worldwide Transportation at the U-M Transportation Research Institute, said in a U-M Sustainability press release that as increased attention is focused on carbon dioxide emissions, there are efforts to improve emission ranking methods since they "inform policy decisions on an international scale. The more comprehensive these rankings are, the better our chances of reducing emissions."

Sivak believes it is important to include local climate. "Because people respond to the climate they live in by heating and cooling indoor spaces, an index that incorporates climate provides a fairer yardstick than an index that does not." Their index adjusts for "heating degree days" and "cooling degree days."

The report explains:

Heating degree days offer an index of the energy demand required to heat indoor spaces. This index is calculated by subtracting the mean daily outdoor temperature from 18 degrees Celsius and summing up only positive values over a fixed period, such as an entire year. Cooling degree days represent an analogous index of the energy demand for cooling.

A surprise find emerged when climate was factored in: The U.S. was no longer among the world's worst CO2 emitters. The nation bounced from one of the bottom dwellers (#152) among the world's 157 countries up to #100 when per capita, GDP and heating-and-cooling-degree-day basis were all considered. (It should be noted the U.S. is far from in the clear. The country still struggles with carbon emissions and recent reports suggest a disturbingly high percentage of children suffering from polluted air, beaches and parks.)

Among other changes, cold-weather countries such as Canada and Russia showed improvement when climate was considered. Countries with mild climates such as Peru and Costa Rica dropped on the list.

As the report notes, there are many different ways to determine which countries emit the most carbon dioxide. Check out this list ranking the U.S. last to see the variations.

Scroll through the list below of the top 10 emitters (ranked from #148-157) by their carbon dioxide emissions per capita, gross domestic product, and heating and cooling degree day. Click here to view the full list.

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  • #148. Kazakhstan

  • #149. Jordan

  • #150. Syria

  • #151. Australia

  • #152. Iraq

  • #153. Bosnia and Herzegovina

  • #154. Turkmenistan

  • #155. Republic of Trinidad and Tobago

  • #156. Uzbekistan

  • #157. South Africa