SEATTLE, Wash. — A proliferation of carbon calculators on the market yields an array of results, even when inputing identical values, according to a recent study.

Researchers from the University of Washington (UW) and Vanderbilt University analyzed 10 carbon calculators used to determine an individual's carbon footprint. The results varied by as much as several metric tons of carbon dioxide (CO2) emissions per activity, and the majority of calculators make it difficult to compare the tools because they fail to disclose information about the different methods and estimates used.

"Calculators can increase public awareness about CO2 emissions and ways to reduce them, and they can affect the type and magnitude of emissions reduction efforts and offset purchases," the report said. "But to the extent that carbon calculators lack transparency, individuals and policymakers will be less able to understand and validate the results."

The Seattle Post-Intelligencer found similar results when it tested a reporter's living habits on the 10 calculators used in the UW study. One calculator from the Bonneville Environmental Foundation pegged the carbon footprint of Reporter Lisa Stiffler and her husband at 75,795 pounds of CO2 annually. In comparison, the U.S. Environmental Protection Agency estimated their annual footprint at 27,029 pounds.

According to the PI, the variation can, in part, be attributed to the calculators' methods of determining emissions related to travel, household electricity consumption and types of behavior.

Another somewhat similar experiment by Consumer Reports showed like results. In February, the publication attempted to measure the emissions from a flight from New York to Los Angeles. The same flight produced 1,924 pounds of CO2 according to TerraPass, and as much as 6,732 pounds of CO2 according to Bonneville Environmental Foundation.