The rate of release of carbon
into the atmosphere today is nearly 10 times as fast as during the
Paleocene-Eocene Thermal Maximum (PETM), 55.9 million years ago, the best
analog we have for current global warming, according to an international team
of geologists. Rate matters and this current rapid change may not allow
sufficient time for the biological environment to adjust.
“We looked at the PETM
because it is thought to be the best ancient analog for future climate change
caused by fossil fuel burning,” said Lee R. Kump, professor of geosciences,
However, the researchers note in Nature Geoscience, that the source of
the carbon, the rate of emission and the total amount of carbon involved in
this event during the PETM are poorly characterized.
Investigations of the PETM are
usually done using core samples from areas that were deep sea bottom 55.9
million years ago. These cores contain layers of calcium carbonate from marine
animals that can show whether the carbon in the carbonate came from organic or
inorganic sources. Unfortunately, when large amounts of greenhouse gases are in
the atmosphere, the oceans become more acidic, and acid dissolves calcium carbonate.
“We were concerned with the
fidelity of the deep sea records,” said Kump. “How do we determine
the rate of change of atmospheric carbon if the record is incomplete? The
incomplete record makes the warming appear more abrupt.”
Kump and his colleagues decided
to look at information coming from areas that were shallow arctic ocean bottom
during the PETM. During a Worldwide Universities Network expedition to train
graduate students from Penn State, the Univ.
of Southampton, Univ.
of Leeds, Univ.
of Utrecht, and Univ.
of Oslo in how projects develop, the
researchers visited Spitsbergen,
uncovered a supply of rock cores curated by a forward-thinking young
coal-mining company geologist, Malte Jochmann.
“Deep-sea cores usually have
from 10 cm to a meter (about 4 inches to 3 feet) of core corresponding to the
PETM,” said Kump. “The Spitsbergen
cores have 150 meters (492 feet) of sediment for the PETM.”
The larger sediment section, made
up of mud that came into the shallow ocean contains organic matter that can
also supply the carbon isotope signature and provide the greenhouse gas profile
of the atmosphere. With the larger core segment, it is easier to look at what
happened through time and ocean acidification would not degrade the contents.
“We think the Spitsbergen core is relatively complete and shows an
interval of about 20,000 years for the injection of carbon dioxide during the
PETM,” said Kump.
Using the data collected from the
cores, the researchers forced a computer model to in essence run backward. They
set up the models to find the proper amounts of greenhouse gases and
atmospheric temperature that would have resulted in the carbon isotope ratios
observed in the cores.
The outcome was a warming of from
9 to 16 F and an acidification event in the oceans.
“Rather than the 20,000
years of the PETM which is long enough for ecological systems to adapt, carbon
is now being released into the atmosphere at a rate 10 times faster,” said
Kump. “It is possible that this is faster than ecosystems can adapt.”