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Climate ChangeGlobal WarmingNatureScience

Ancient Climate Change Greened Antarctica

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Ancient Antarctica was much warmer and wetter than was previously thought, according to a new study just released in the journal Nature Geoscience. The climate supported lush vegetation, including stunted trees, along Antarctica’s coastline.

The research was done by the University of Southern California in Los Angeles, and included researchers from NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and Louisiana State University in Baton Rouge.

Examining the plant leaf wax remnants in sediment core samples that were taken from beneath the Ross Ice Shelf, the researchers found that summer temperatures along the Antarctic coast 15 to 20 million years ago were 20 degrees Fahrenheit (11 degrees Celsius) warmer than today, with temperatures getting as high as 45 degrees Fahrenheit (7 degrees Celsius). The researchers also found that the precipitation levels then were several times higher than today.

“The ultimate goal of the study was to better understand what the future of climate change may look like,” said Feakins, an assistant professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences. “Just as history has a lot to teach us about the future, so does past climate. This record shows us how much warmer and wetter it can get around the Antarctic ice sheet as the climate system heats up. This is some of the first evidence of just how much warmer it was.”

The researchers began to suspect that high-latitude temperatures during the middle Miocene epoch would have been warmer than previously thought when study co-author Sophie Warny, an assistant professor at LSU, found large quantities of pollen and algae in the sediment cores taken in Antarctica. Fossils of plant life in Antarctica are rare because the massive ice sheets and climate change there grind and scrape away everything as they slowly move.

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“Marine sediment cores are ideal to look for clues of past vegetation, as the fossils deposited are protected from ice sheet advances, but these are technically very difficult to acquire in the Antarctic and require international collaboration,” said Warny.

Because of the tiny pollen samples, Feakins chose to look at the remnants of leaf wax taken from sediment cores for insight into the climate then. Leaf wax works as a record of climate change by documenting the hydrogen isotope ratios of the water that the plant absorbed while it was alive.

“Ice cores can only go back about one million years,” Feakins said. “Sediment cores allow us to go into ‘deep time.'”

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Using a modified version of a model that was originally developed to analyze hydrogen isotope ratios in atmospheric water vapor data from NASA’s Aura spacecraft, co-author and JPL scientist Jung-Eun Lee made experiments aimed at finding out how much warmer and wetter climate they climate would have likely been.

“When the planet heats up, the biggest changes are seen toward the poles,” Lee said. “The southward movement of rain bands associated with a warmer climate in the high-latitude southern hemisphere made the margins of Antarctica less like a polar desert, and more like present-day Iceland.”

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Between 16.4 and 15.7 million years ago, the peak of this Antarctic greening occurred, during the middle Miocene period. Which was long after the age of the dinosaurs — most dinosaurs became extinct around 64 million years ago.

The Miocene epoch, was dominated by mostly modern-looking animals; like horses, deer, camel and many different species of apes. With very recognizably human-looking and -acting apes emerging at least 2 million years ago.

The warm climate during the middle Miocene is associated with carbon dioxide levels of around 400 to 600 parts per million (ppm). Today, in 2012, carbon dioxide levels have just passed 400 ppm, which is the highest they’ve been in at least several million years. If current emission rates continue (they are likely to rise much further), the atmospheric carbon dioxide levels will reach middle Miocene levels by the end of this century.

The high carbon dioxide levels present during the middle Miocene epoch have been documented in many studies, using many different lines of evidence. This includes the number of microscopic pores on the surface of plant leaves and other geochemical evidence from soils and marine organisms. While researchers do not yet know exactly why carbon dioxide was at these levels during the middle Miocene, the high carbon dioxide levels coincide very clearly with the global warmth that is documented from many parts of the world during this period in Earth’s history.

Source: NASA/JPL
Image Credits: Louisiana State University, University of Nebraska-Lincoln, Sophie Warny and Kate Griener (Louisiana State University, Baton Rouge), NASA/JPL-Caltech/Dr. Philip Bart, LSU




6 comments
  1. Gabriel B. Atega

    If forests covered the lands of the Earth up to the poles: Antarctica in the South and Siberia and Canada in the North that should translate to CO2 bound up in tree trunks, branches, leaves and ground deposits of dead leaves and plant material. How come the CO2 levels were up to 400 ppm when there were then no cars and trucks and industries with CO2 emissions to be concerned about. How come the Earth was warm without humans around? Connecting the findings with present atmospheric conditions is unscientific. The Earth will warm naturally because it has done so in the past. And it will again freeze because it has also happened in the past.

    If the poles were that warm, what would be the temperature levels in the tropics?

    If the forests covered the Earth’s land surfaces several times the present; it should also be considered that these trees produced oxygen and would have compensated for the presence of CO2. There should be another element in the atmosphere that is causing the elevated temperatures. How about water vapor? Water absorbs heat twice that of CO2 and quantity wise given the extent of the forests should be somewhere at 50,000 ppm. What is the estimate of water vapor in the atmosphere 15 million years ago?

    1. Zachary Shahan

      I love it when readers put forth completely simplistic arguments and act as if they were never considered by climate scientists. A wonder.

      Yes, the Earth has been warm in the past, but the present warming is clearly caused by humans. (See: http://planetsave.com/2012/01/19/what-is-causing-global-warming/) Furthermore, the warming is occurring at a very concerning rate that will lead to catastrophe for the human species if we don’t get it under control very soon. That is the concern.

      For info on water vapor, check out: http://www.skepticalscience.com/water-vapor-greenhouse-gas.htm

      For more reading, I’d recommend: http://www.skepticalscience.com/climate-change-little-ice-age-medieval-warm-period.htm

      and: http://www.skepticalscience.com/CO2-is-not-the-only-driver-of-climate.htm

    1. Anderlan

      A difference of 20F is equal to a difference of 11C. And a measured temperature of 45F, where 32F is the freezing point of water, is equal to a measured temperature of 7.2C, where 0C is the freezing point of water.

      For differences: 1F = 0.555.. C, 1C = 1.8F

      For measured temperatures, and only for that, add the following wrinkle to your algebra: 0C = the freezing point of water, 32F = the freezing point of water.

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