Carbon dioxide emissions from fossil fuels are the most significant greenhouse gas emissions in Pennsylvania according to the Greenhouse Gas Emissions Inventory for Pennsylvania prepared by Penn State researchers.

"In 1999, this category (fossil fuel generated carbon dioxide) contributed 90.53 percent of the total," the researchers reported. "Despite their large contribution to the total, greenhouse gas emissions from fossil fuels increased less than 1 percent between 1990 and 1999."

However, between 1990 and 1999, Pennsylvania's total greenhouse gas emissions increased 3 percent.

"While Pennsylvania's share of the national total greenhouse gas emissions has been declining, its contribution is still above the national average on a per capita basis," the researchers report.

In 1998, Pennsylvania was fourth among states in production of carbon dioxide and only 12 countries produced more carbon dioxide than Pennsylvania.

The inventory also demonstrates that motor vehicles are the fastest growing source of greenhouse gases in Pennsylvania. While the population in Pennsylvania is not growing, the number of miles traveled is rising.

The Greenhouse Gas Emissions Inventory, funded by the Pennsylvania Department of Environmental Protection and conducted by Penn State's Center for Integrated Regional Assessment, part of the College of Earth and Mineral Sciences Environment Institute, looked at six major categories of greenhouse gas emissions for the years 1990 and 1999.

The six categories were carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride. The researchers were Dr. Adam Z. Rose, professor of geography, Dr. Brent Yarnal, professor of geography and director of CIRA, Robert Neff, graduate student in geography and research associate in CIRA, and Howard Greenberg, visiting senior scientist, CIRA. They followed guidelines established by the U.S. Environmental Protection Agency.

The researchers found that none of the categories except carbon dioxide generated more than 5 percent of total emission.

Most scientists believe that greenhouse gases contribute significantly to long-term warming of the Earth's atmosphere. Long-term warming will most likely negatively affect agriculture, forests, wildlife and human health. While activities such as conservation are relatively cost free, most efforts to control greenhouse gas emissions are not and have wide-ranging implications.

The social and political effects of reducing greenhouse gas emissions are complicated. The researchers note that a significant portion of the economic activity that generates greenhouse gases, such as generation of electricity, is exported to customers in other states. The "geographic responsibility" of these emissions is not clear-cut.

The Inventory is intended to increase the awareness of policy makers and others in Pennsylvania on the state's role in greenhouse gas emissions and what can be done where to reduce these emissions.