Are we heading towards the same disaster?
By
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.
References:
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