A global climate change affecting Earth for about 150,000 years could have happened 56 million years ago due to the release of massive amounts of carbon from methane hydrate that was frozen under the seafloor.

Researchers at Rice University noted that the Earth's ecosystem changed during the Paleocene-Eocene Thermal Maximum (PETM) that happened 56 million years ago when at least 2,500 gigatonnes of carbon were released into the ocean and atmosphere.

According to the study, Earth's temperature rose by as much as 6 degrees Celcius and this affected the planet for 150,000 years, with many species becoming extinct, until excess carbon was reabsorbed into sediment, the researchers said.

The Rice scientists suggest that there could be as much methane-containing gas hydrates then as there is now. Thus, there is a concern that continued burning of fossil fuels by humans could someday trigger another feedback loop that disturbs the stability of methane hydrate under the ocean.

This change could warm the atmosphere and prompt the release of large amounts of methane, a more powerful greenhouse gas than carbon dioxide.

"The amount of carbon released then is on the magnitude of what humans will add to the cycle by the end of, say, 2500. Compared to the geological timescale, that's almost instant. We run the risk of reproducing that big carbon-discharge event, but faster, by burning fossil fuel, and it may be severe if hydrate dissociation is triggered again," Guangsheng Gu, lead author of the research, said

The research team is composed of Gerald Dickens, a Rice professor of Earth science; graduate student Guangsheng Gu, who is lead author; Walter Chapman, William W. Akers Professor in Chemical Engineering; George Hirasaki, A.J. Hartsook Professor in Chemical Engineering; and alumnus Gaurav Bhatnagar, all of Rice; and Frederick Colwell, a professor of ocean ecology and biogeochemistry at Oregon State University.

The research is supported by the United States Department of Energy.