Southeast may be headed toward tipping point with carbon footprint: researchers

In a paper published recently in the journal Ecosystems, a team led by Auburn University School of Forestry and Wildlife Sciences researchers found that the southeast region of the United States could be close to a turning point in terms of its carbon footprint.

"What makes the findings so important and relevant to policy, says Hanqin Tian, lead author of the study, is that it is the first study to look at multiple factors affecting regional climate and carbon storage over an extended period of time.

Tian, the Alumni and Solon Dixon Professor in Auburn University's School of Forestry and Wildlife Sciences, developed a computer model that makes it possible to understand the intricate ways that climate change, atmospheric carbon dioxide, ozone, nitrogen and land use changes work together. The Dynamic Land Ecosystem Model is a new generation of land ecosystem models to address multiple environmental stresses and changes over time.

"This is the first time in the last century that we have fully evaluated the impacts of human and natural factors on Southern ecosystems including forests," said Ge Sun of the USDA Forest Service and one of the researchers involved in the project.

Over time, the Southeast has been transformed from being a source of carbon emissions to being a carbon sink. This means that, overall, the environment in the Southeast removes carbon from the atmosphere rather than contributes to it.

One of the surprising things the study revealed was that air pollution – carbon and nitrogen in the atmosphere – was one of the key factors in rapid forest growth that turned the area into a carbon sink. However, the study also suggests that there is a tipping point at which fertilization effect from air pollution will begin to harm rather than help regional ecosystems, especially when considered alongside land use changes and heightened drought intensity.

"For the last few years, people haven't worried about this region," Tian says. "They think it is not an immediate problem."

The research team, however, has found there is reason to be alert to the possibility that the situation in the Southeast could change. The current changes in land use are causing a major shift in carbon storage dynamics; cities are growing and the Southeastern landscape is changing at a rapid pace.

Tian says that careful urban and air quality planning is needed to address how and where our cities grow. Although the Southeast leads the nation in carbon storage at present, the switch could flip sooner than anyone expects without thoughtful preparation for the future.

Support for the project was provided by the U.S. Department of Energy National Institute for Climate Change Research Program, NASA Interdisciplinary Science Program, NASA Terrestrial Ecology Program, Alabama Agricultural Experiment Station Research Program and the Southern Forest Research Partnership.