Some 56 million years ago, both ocean and surface temperatures on Earth began to rise. The period of global warming known as the Paleocene-Eocene Thermal Maximum lasted approximately 100,000 years.

New research questions whether the release of methane from the ocean floor fully explains this mysterious moment of climate change.

Much of the planet's methane is found in beneath the ocean floor, trapped in an ice-like material called hydrate. When the ocean warms, the frozen methane melts and is released, traveling toward the surface.

The ancient shells of fossilized deep ocean creatures offer a history of the ocean's changing chemical composition. Previous fossil surveys support the theory that a large amount of methane was released from the ocean floor during the Paleocene-Eocene Thermal Maximum.

But new computer models call into question whether such a release would translate to the kind of warming measured at the surface. Even a sudden or rapid outburst beneath the ocean crust would take time to reach the seafloor and ascend the water column, new simulations show.

"This is because the methane gas formed by hydrate melting below the sea floor takes time to travel up to the seabed, and on the way it can refreeze or dissolve and then be consumed by microbes that live below the seabed," Tim Minshull, a professor of Earth and ocean sciences at the University of Southampton, said in a news release. "Only a fraction of the methane may escape into the ocean and the part that does escape may take thousands of years to do so."

"Our results show that hydrate melting can indeed be triggered by ocean temperature change, but the result is not necessarily a rapid outburst of methane," Minshull added.

Researchers published their findings this week in the journal Geophysical Research Letters.

"To explain the geological observations by melting of hydrate, much more hydrate must have been present globally than is perhaps reasonable for such a warm late Palaeocene Ocean," said study co-author Paul Wilson, head of Southampton's palaeoceanography and palaeoclimate research group. "And special transport routes would have been needed -- perhaps cracks and fissures -- to allow the methane to rise to the seabed quickly."

The study doesn't offer solutions so much as raise questions.

"They raise important questions about the potential for breakdown of present-day methane hydrates to exacerbate climate change," Minshull said.

Because current trends are being compared to mechanisms at play during the Paleocene-Eocene Thermal Maximum, scientists say it's important to gain a better understanding of why and how ocean temperature rose 56 million years ago.