Researchers Uncover Accounting Error in Global Carbon Budget

An international team of scientists has released data indicating that greenhouse gas uptake by continents is less than previously thought because of methane emissions from freshwater areas.

The study, published in the journal Science, indicates that methane gas
release from freshwater areas is higher than previous estimates. Past analyses of carbon and greenhouse gas exchanges on
continents failed to account for the methane gas that is naturally
released from lakes and running water. The new study indicates the net absorption of greenhouse
gases by natural continental environments, such as forests, is at least
25% less than previously estimated.

John Downing, an Iowa State University professor in the ecology, evolution and organismal biology department, is part of the research team. He also has conducted research measuring the amount of carbon sequestered in lake and pond sediment. This new study gives scientists a better understanding of the balance between carbon sequestration and greenhouse gas releases from fresh water bodies.

"Methane is a greenhouse gas that is more potent than carbon dioxide in the global change scenario," Downing said. "The bottom line is that we have uncovered an important accounting error in the global carbon budget. Acre for acre, lakes, ponds, rivers and streams are many times more active in carbon processing than seas or land surfaces, so they need to be included in global carbon budgets."

Methane emissions from lakes and running water occur naturally, but have been difficult to assess, according to David Bastviken, principal author and professor in the department of water and environmental studies, at Linköping University in Sweden.

Small methane emissions from the surfaces of water bodies occur continuously, but "Greater emissions occur suddenly and with irregular timing, when methane bubbles from the sediment reach the atmosphere, and such fluxes have been difficult to measure," Bastviken said.

The greenhouse effect is caused by human emission of gasses that act like a blanket and trap heat inside the Earth’s atmosphere, according to the International Panel on Climate Change. Some ecosystems, such as forests can absorb and store greenhouse gasses. The balance between emissions and uptake determine how climate will change. The role of freshwater environments has been unclear in previous budgets, Downing said.

The researchers studied methane fluxes from 474 freshwater areas and calculated emission based on new estimates of the global area covered by inland waters.