From Greenhouse to Icehouse

From Greenhouse to Icehouse
The findings of this research indicate that even as the poles started to cool during the late Eocene, the sea surface temperatures in the tropical regions remained fairly stable. Credit: NASA

A new study that reconstructed ocean temperatures from millions of years ago could provide new insight into how the Earth responds to climate change.

It is often said that the past is the key to the future. For climate scientists, understanding how the Earth’s climate changed and evolved millions of years ago could help predict future climate change.

In a study published in the journal Nature, scientists reconstructed ocean temperatures during a time when the Earth transitioned from a greenhouse world to an icehouse world.

“In the early Eocene, between 53 and 49 million years ago, the Earth experienced the warmest climates of the past 100 million years,” says lead author Peter Bijl of Utrecht University. “After this super-greenhouse, global climates started a gradual cooling trend. This cooling persisted in the late Eocene.”

The scientists found that during that time, as sea surface temperatures (SSTs) in the higher latitudes cooled, temperatures in the mid-latitudes or the tropical regions stayed fairly stable. Theoretically, the authors say, the tropics should have cooled as well. This finding brings into question the role that a decrease in concentrations of atmospheric greenhouse gases, such as , had on cooling the poles.

“There must be a mechanism that we don't know up to now that is able to increase the temperatures at high latitudes without increasing the CO2 forcings at low latitudes,” says Bijl.

Earth on the Rocks

Towards the end of the Eocene, the Earth had started to cool, and the first Antarctic ice sheets started to form during the early Oligocene, approximately 33 million years ago. Scientists, however, know very little about this climate transition. Their knowledge of what occurred in the lower latitudes is especially lacking because there are fewer ways to reconstruct past temperatures in that part of the globe.

Speaking about the cooling that the world experienced during the end of the Eocene, Bijl says, “We don't know much about why it cooled down that much, how or how fast.”

The warm conditions that existed throughout much of the Eocene allowed land mammals to flourish, and the first primates evolved during this time. By the end of the Eocene, most modern-day mammals had evolved. The transition from the greenhouse Eocene to the ice-house Oligocene represents one of the most dramatic climate change events in recent geologic history.

“We know the climate has changed much more radically in the past,” says Gavin Schmidt, climate modeler at NASA’s Goddard Institute for Space Studies. “Where we're expecting climate to go in the future is outside the range for what we have data for.”

That is where studies like Bijl’s could play a role. Studying climate change during the transition from a greenhouse world to an icehouse world could help climate scientists grappling with present-day climate change understand how the Earth responds to major climate events.

“To test our theories, to understand the impact of change to the ecosystem, it’s vitally important that we maintain research into past climates, precisely because we don’t know where we’re going in the future,” says Schmidt.

From Greenhouse to Icehouse
Position of the continents during the Eocene (55.8 to 33.9 Ma). Credit: Bristol University

Taking Temperature over Time

Studying such ancient events is by no means easy. Scientists need access to temperature data, and that presents one of the main problems of studying climate change that occurred millions of years ago. Thermometers were invented around 400 years ago, and most instrumental records of temperature only date back to the nineteenth century. To study the Earth’s climate farther back in time, scientists use proxy data, or data collected from natural recorders of climate change. Some examples of proxy data include tree rings, ice cores, fossil pollen and ocean sediment, among others.

Bijl and the research team used two organic proxies to reconstruct SSTs. The TEX86 proxy, developed by the NIOZ Royal Dutch Institute for Sea Research, is an index based on lipids produced by microbes that dwell near the sea surface. This lipid index was devised to determine SST from marine sediments. The Uk,37 proxy is another paleothermometer based on a highly resistant organic compound produced by marine organisms such as algae. The researchers obtained ocean sediment samples from the East Tasman Plateau in the Southwest Pacific. The sediment cores were obtained by the Integrated Ocean Drilling Program in 2000.

The data obtained by Bijl’s team show that SSTs in the southwest Pacific rose to about 35 degrees Celsius during the early Eocene and gradually dropped to approximately 21 degrees Celsius towards the late Eocene, while SSTs in the tropical regions stayed relatively constant throughout. The question is why the temperatures in the tropics changed very little during the Eocene even as the rest of the world was undergoing a more drastic cooling.

The common belief is that high atmospheric greenhouse gases such as carbon dioxide brought about the warm temperatures during the early Eocene. Similarly, the global cooling that took place during the mid to late Eocene, scientists believe, was a result of the decline in carbon dioxide levels in the atmosphere. But if lower levels of CO2 didn’t lead to cooler temperatures in the tropics, then some additional positive feedbacks must have increased the cooling effect in the poles. Scientists are looking to climate models for a solution.

Mix and Match Models

There’s just one problem with using climate models to figure out what happened in the past: the models don’t always reflect reality. In fact, Bilj says that climate models for polar during the Eocene don’t match their data from the southern oceans.

“What they get out of their models is a much higher SST gradient than we find in our data,” he explains. “That means there are some mechanisms that are missing in the models.”

Given this mismatch, Bijl says it’s frightening that scientists rely so heavily on computer models to predict future climate patterns. He says that is why it’s crucial to make sure the models are as accurate as they can be, and he hopes that the collaboration that’s currently taking place between climate modelers and other scientists will help to fill the gaps in existing models.

Schmidt notes that in such collaborations, modelers work closely with scientists in many different fields to determine what might be missing and to identify processes that were previously neglected.

“The kinds of models we're using today are more sophisticated than 10 years ago,” Schmidt says. “We’re hopeful they might provide answers that were elusive in the past. But they haven’t provided (those answers) yet.”

Whatever happens to the climate in the future, based on the past history of our planet, some change is inevitable. During its approximately 4.5-billion-year history, the Earth has undergone numerous natural shifts in climate change, and Bijl says the current climate crisis is another one of those events. Though he admits present-day climate change is occurring at a much faster pace, Bijl says it is not a new experience for the Earth.

“Whatever scary things everyone says about , the world has experienced much worse,” he says. “Many life forms may go extinct, but the world will keep spinning, and new life will evolve.”

Source:, by Anuradha K. Herath

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Citation: From Greenhouse to Icehouse (2009, November 24) retrieved 17 October 2019 from
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User comments

Nov 24, 2009
"Many life forms may go extinct, but the world will keep spinning, and new life will evolve.” Cold comfort as human genes may not be a part of this life.

Nov 24, 2009
This comment has been removed by a moderator.

Nov 24, 2009
Science depends on finance from the economy, which is dependent on the oil/plastic/drug/food/water/gas/electricity interdependent industries that support modern human life - worldwide. The economy also maintains a minority of humans in control of those industries, and in control of the lives of the majority of humans as a direct result. The minority fights continuously against a wide range of forces to maintain their control, and are currently treating environmental change and social response as just another threat. Some are making small superficial changes to maintain popularity with the majority, but the old economic drivers are still outgrowing the social response.

The controlling minority does a serious, centralised, credible evaluation of the cause of environmental changes, the current environment cycle and the human contribution (direct and indirect) and finally unite to make single global decisions leading to implemented changes in all human society.

Perhaps they already have.

Nov 24, 2009
"“We don't know much about why it cooled down that much, how or how fast.” "

Late Eocene saw two 90+km diameter astroblemes form. Chesapeake Bay, USA at 35 +- 1.1mya and Popigai, Russia, 37 +- 2.3mya.

Nov 24, 2009
Apologies for rambling. The middle. Paragraph of my comment above was suposed the start "The minority needs to "...

For the majority, the whole subject has become too confused. The economy protectorate are very focussed on maintaining existing systems, and justify it with stories of economic collapse, chaos and return to fractured control systems. However, if the really are ignoring the science being published currently, all of their protection of the economy and their control is going to yield nothing. Whether we are doing it or not, Earth is changing her clothes, and perhaps the "noble human" is about to learn the true value of its money, its economy and its illusion of control.

By the way, has anyone seen the anymore pictures or news about supposed skeletal remains of Noah's Ark atop of Mount Ararat in eastern Turkey? Did that group from Hawaii finally do their expedition to prove the existance of those remains?

Curiousity might yet save the cat's companion. ;-)

Nov 24, 2009
PS: Could someone at PhysOrg please try the editing facility on an iPhone or similar? The comment text box could really benefit from a scroll bar, or auto-resizing.

Kind Regards, etc ...

Nov 24, 2009
Just in case anyone still is a believer in Man Made Global warming, the scam has been exposed...



Nov 25, 2009
"�We don't know much about why it cooled down that much, how or how fast.� "

Late Eocene saw two 90+km diameter astroblemes form. Chesapeake Bay, USA at 35 +- 1.1mya and Popigai, Russia, 37 +- 2.3mya.

As I understand it, though, the climate was cooling for millions of years before those impacts--I mean, I'm not saying that they weren't likely to have had a big influence, maybe even a long-term one, but they weren't the only factors at play. Interesting, though; never heard of the latter impact before. Google time!

Nov 25, 2009
Thankfully the search for ancient terrestrial impacts by large meteorites has gained much momentum, with Google Earth and the huge array of satellites fotographing nearly every acre of land, and many peering under the water to find where (an instinctive estimate would say) sixty percent of the impacts must have taken place. Linking the impacts to earthquakes and volcanism is also beginning in earnest, so we might learn why the climate has shifted in the past - with or without the GreenHouse mechanism.

This can yield two useful peices of information. One, isolating the GreenHouse events and the conditions experienced as a result of them. Two, the survival and recovery rates for vegetable and animal life at the end of the different climate changes.

Additionally, (intriguingly), we can see that at the time when life on Earth has developed to the point of being able to protect the planet from predictable impacts, we decide (in greed & ignorance) to destroy the planet by other means.

Nov 25, 2009
"Many life forms may go extinct, but the world will keep spinning, and new life will evolve.� Cold comfort as human genes may not be a part of this life.

Man would survive a nuclear war. A little warming will be good. More crops = more food.

No. I do not believe the HORROR. Just another method for government to separate me from what's mine.

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