Pliocene Hot Age?
,By studying fossilized mollusks from some 3.5 million years ago, UCLA geoscientists and colleagues have been able to construct an ancient climate record that holds clues about the long-term effects of Earth's current levels of atmospheric carbon dioxide, a key contributor to global climate change. Two novel geochemical techniques used to determine the temperature at which the mollusk shells were formed suggest that summertime Arctic temperatures during the early Pliocene epoch (3.5 million to 4 million years ago) may have been a staggering 18 to 28 degrees Fahrenheit warmer than today. These ancient fossils, harvested from deep within the Arctic Circle, may have once lived in an environment in which the polar ice cap melted completely during the summer months. The Pliocene Epoch is the period in the geologic timescale that extends from 5.3 million to 2.6 million years before the present time.
"Our data from the early Pliocene, when carbon dioxide levels remained close to modern levels for thousands of years, may indicate how warm the planet will eventually become if carbon dioxide levels are stabilized at the current value of 400 parts per million," said Aradhna Tripati, a UCLA assistant professor in the department of Earth and space sciences and the department of atmospheric and oceanic sciences.
The mid Pliocene warm period is considered a potential analog of future climate change. The intensity of the sunlight reaching the earth, the global geography, and carbon dioxide concentrations were similar to present levels. Model simulations of mid-Pliocene climate produce warmer conditions at middle and high latitudes, as much as 10—20°C warmer than today, above 70°N. They also indicate little temperature variation in the tropics.
The global average temperature in the mid-Pliocene was 2—3°C higher than today, global sea level 25 meters higher and the Northern hemisphere ice sheet ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 million years ago.
The results of this study lend support to assertions made by climate modelers that summertime sea ice may be eliminated in the next 50 to 100 years, which would have far-reaching consequences for Earth's climate, she said.
The research, federally funded by the National Science Foundation, is scheduled to be published in the April 15 print issue of Earth and Planetary Science Letters, a leading journal in geoscience, and is currently available online.
"The Intergovernmental Panel on Climate Change identifies the early Pliocene as the best geological analog for climate change in the 21st century and beyond," said Tripati, who is also a researcher with UCLA's Institute of the Environment and Sustainability and Institute of Geophysics and Planetary Physics. "The climate-modeling community hopes to use the early Pliocene as a benchmark for testing models used for forecasting future climate change."
Ice sheets and sea ice in polar regions reflect incoming solar radiation to cool the Earth — a phenomenon that makes the poles incredibly sensitive to variations in climate, she said. An increase in Arctic temperatures would not only cause the ice sheets to melt but would also result in the exposed land and ocean absorbing significantly more incoming solar energy and further heating the planet.
The research was conducted on mollusk fossils collected from Beaver Pond, located in the Strathcona Fiord on Ellesmere Island, at the northernmost point of Canada, which is well within the Arctic Circle. Named for the numerous branches discovered with beaver teeth marks that have lasted for millions of years, Beaver Pond has proven to be a treasure trove of fossilized plant and animal specimens that remain remarkably well-preserved within a peat layer encased in ice, Tripati said.
"Ice cores are a remarkable archive of past climate change because they can give us direct insights into how the poles have responded to variations in past greenhouse gas levels," Tripati said. "However, ice core data is available for only the past 800,000 years, during which carbon dioxide levels were never above 280 to 300 parts per million. To understand environmental change for earlier time periods in Earth's history when carbon dioxide levels were near 400 parts per million, we have to rely on other archives."
By measuring the isotopic content of oxygen in a combination of fossilized mollusk and plant samples, it is possible to determine the temperature at which the specimens originally formed, Tripati said. While this method enables climate reconstructions dating back millions of years without the need for ice core samples, it is uncommon to find a site that contains both plant and shell specimens from the same time and place.
For further information: http://www.eurekalert.org/pub_releases/2011-04/uoc--afh040711.php