Monday, September 24, 2012

Climate which changed the world 56 million years ago.

Are we heading towards the same disaster?
Dr. Nitish Priyadarshi

The Eocene was much like the garden of Eden.

56 million years ago a mysterious surge of carbon into the atmosphere sent global temperatures soaring. In a geologic eyeblink life was forever changed.

Climate change is changing the world. Either it is in the form of temperature rise or in the form of severe floods. Many times question arises in my mind whether this climate change is the out come of present human activities on the earth or it has happened in early geological ages too. Answer is “yes” climate change has occurred several times from the beginning of the earth formation. Evidences are preserved in from of rocks, sediments, and fossils.

Studying the records of past climate change will fill you like reading thriller novel in which every chapter is full of suspense and thrill. Every chapter of this novel denotes different geological periods with different stories of climate change.

My article is about the chapter which covers the story of climatic conditions around 56 million years ago.

The Atlantic Ocean had not fully opened, and animals, including perhaps our primate ancestors, could walk from Asia through Europe and across Greenland to North America. They wouldn’t have encountered a speck of ice; even before the events we’re talking about, earth was already much warmer than it is today. But as the Paleocene epoch gave way to the Eocene, it was about to get much warmer still-rapidly, radically warmer.

The cause was a massive and geologically sudden release of carbon. Just how much carbon was injected into the atmosphere during the Paleocene-Eocene Thermal Maximum, or PETM, as scientists now call the fever period, is uncertain. But they estimate it was roughly that amount that would be injected today if human beings burned through all the earth’s reserves of coal, oil and natural gas. The PETM lasted more than 150,000 years, until the excess carbon was reabsorbed. It brought on drought, floods, insect plagues, and a few extinctions. Life on earth survived-indeed, it prospered- but it was drastically different. Climate zones shifted toward the poles, on land and at sea, forcing plants and animals to migrate, adapt or die. Some of the deepest realms of the ocean became acidified and oxygen-starved, killing off many of the organisms living there. It took nearly 200,000 years for the earth’s natural buffers to bring the fever down. Today the evolutionary consequences of that distant carbon spike are all   around us; in fact they include us. Now we ourselves are repeating the experiment.

The PETM is significant because it marks the beginning of a 20+ million year warming trend that takes place in the Eocene, and continues on through the Oligocene. That isn't to say that the PETM lasted for 20+ million years, and was responsible for the warm balmy weather in the Eocene, but it did have an effect on the creatures living at the time, especially microscopic ocean organisms.

30-40% of foraminifera species went extinct during this time. Foraminifera are microscopic plankton-like organisms that feed much of the rest of the food chain.

According to a recent study led by Goethe University and the Biodiversity and Climate Research Centre (BIK-F) in Frankfurt, Antarctica had a much warmer climate during the Eocence Epoch (56-34 million years ago), enough to support subtropical flora and fauna.
Published in Nature, the study looked at sediment from cores dating back between 55 and 46 million years ago drilled off the coast of Antarctica near Wilkes Land (part of Antarctica located south of Australia) in 2010 as part of the Integrated Ocean Drilling Programme.

Scientists believe that global atmospheric carbon dioxide (CO2) concentrations were significantly higher (as much as 1,000 parts per billion) than present (which are just under 400 parts per billion). They don’t yet know what caused the major surge in CO2 levels at the start of the Eocene and exactly why they began to abate.

Hundreds of scientific papers have been published on the PETM, but because of the scarcity of paleo-data from this time, there has been no clear scientific agreement over what initiated this warming, or where all the CO2 came from.  

Where did all the carbon come from? We know the source of the excess carbon now pouring into the atmosphere: us. But there were no humans around 56 million years ago, no cars no power plants. Many sources have been suggested for PETM carbon spike, and given the amount  of carbon, it likely came from more than one. At the end of the Paleocene, Europe and Greenland were pulling apart and opening the North Atlantic, resulting in massive volcanic eruptions that could have cooked carbon dioxide out of organic sediments on the seafloor. Wildfires might have burned through Paleocene peat deposits, although so far soot from such fires has not turned up in sediment cores. A giant comet smashing into carbonate rocks also could have released a lot of carbon very quickly, but as yet there is no direct evidence of such an impact.

The oldest and still the most popular hypothesis is that much of the carbon came from large deposits of methane hydrate, a peculiar, ice like compound that consists of water molecules forming a cage around a single molecule of methane. Hydrates are stable only in a narrow band of cold temperatures and high pressures; large deposits of them are found today under the Artic tundra and under the sea floor, on the slopes that link the continental shelves to the deep abyssal plains. At the PETM an initial warming from somewhere –perhaps the volcanoes, perhaps slight fluctuations in Earth’s orbit that exposed parts of it to more sunlight- might have melted hydrates and allowed methane molecules to slip from their cages and bubble into the atmosphere.

Many of the other climate feedbacks that we either already observe today or expect to experience probably took place during the PETM warming, as well. Severe drought would have led to increased wildfires, injecting more carbon into the atmosphere. Some research shows that permafrost on a then glacier-free Antarctica thawed, which would have also released carbon dioxide and methane. Another interesting source of carbon that some scientists hypothesize is the burning of peat and coal seams. Peat is decayed vegetation and has a very high carbon content. Peat, which is found in the soil beneath the surface, can be ignited by something like a wildfire and continue to smolder for as long as centuries. Coal seams can be ignited in a similar way, and burn for decades to centuries, releasing huge amounts of carbon into the atmosphere.

The consequences of the PETM were significant in magnitude and truly global in scope:

1. Global warming; atmospheric temperatures warmed by 5°-9°C globally (6°-9°C warming of southern high latitude sea surface temperatures, 4°-5°C warming of the deep-sea, tropical sea surface temperatures, and Arctic Ocean, and ~5°C warming mid-latitude continental interiors).

2. Perhaps the most staggering result was that at times during the early Eocene warm episode the Arctic sea surface temperature soared to 24°C. The evidence suggests that the PETM marked possibly the warmest time at the North Pole for over 100 million years—certainly it has not been as warm since. Today's circum-polar ecosystems could not exist in such a climate regimen.

3. Ocean acidification (the carbonate compensation depth [CCD] rapidly shoaled by more than 2 km [<10 and="and" gradually="gradually" recovered="recovered" years="years">100,000 years)).

4. Sudden onset of anoxic conditions in deep ocean waters..

5. Increased intensity of the hydrologic cycle and erosion rates (based in part on changes in clay mineral assemblages).

6. Major extinctions of benthic foraminifera in the deep-sea (30-50% of species). Turnover and evolution of calcareous plankton (calcareous nannofossils and planktic foraminifers).

7. Migration of terrestrial organisms to the high latitudes.

8. Turnover and evolution of terrestrial animals and plants. New mammal lineages first appear in the earliest Eocene, including the earliest horse in North America.

The hypothesis is alarming. Methane in the atmosphere warms the earth over 20 times more per molecule than carbon dioxide, then after a decade or two, it oxidizes to C02 and keeps on warming for a long time. Many scientists think just that kind of scenario might occur today: The warming caused by the burning of fossil fuels could trigger a runway release of methane from the deep sea and the frozen north.