A new study by a University of Hawaii oceanographer is offering a sobering reconsideration of the long-term impacts of burning fossil fuel.

According to author Richard Zeebe, global warming from fossil-fuel burning could be more intense and longer lasting than previously believed. The study is published in the journal Proceedings of the National Academy of Sciences.

Previous studies have found that current atmospheric carbon dioxide concentrations are 40 percent higher than preindustrial levels, largely because of fossil-fuel burning and other human activities.

Zeebe’s study relies on analysis of past climate episodes to gain a more nuanced understanding of how such an increase might affect global warming. By examining how so-called climate feedbacks such as land ice or vegetation evolve in relation to how surface temperatures rise as a result of changing carbon dioxide levels, Zeebe concluded that the consequences of fossil-fuel burning — such as ice melt and changes in sea level — may be felt over hundreds of thousands of years.

"The calculations showed that man-made climate change could be more severe and take even longer than we thought before," Zeebe said. "Politicians may think in four-year terms but we as scientists can and should think in much longer terms. We need to put the impact that humans have on this planet into a historic and geologic context."