This 2012 peer reviewed study is further paleoclimate evidence of polar amplification from greenhouse warming. Atmospheric CO2 levels between 400 to 600 ppm during the Miocene, is the range where anthropogenic CO2 emissions will force our contemporary atmosphere in a matter of a few decades. NASA news story explicating this study lower down:<br>
<br><a href="http://www.nature.com/ngeo/journal/v5/n8/full/ngeo1498.html">http://www.nature.com/ngeo/journal/v5/n8/full/ngeo1498.html</a><br><h1 class="article-heading">Hydrologic cycling over Antarctica during the middle Miocene warming</h1>
<dl class="citation"><dd class="journal-title">Nature Geoscience</dd><dd class="volume">
5<span>,</span></dd><dd class="page">557–560</dd><dd>(2012)</dd><dd class="doi">doi:10.1038/ngeo1498</dd></dl>
<dl class="citation dates"><dt class="received first">Received</dt><dd>
25 August 2011
</dd><dt class="accepted">Accepted</dt><dd>
15 May 2012
</dd><dt class="published-online">Published online</dt><dd>
17 June 2012
</dd></dl>From 20 to 15 million years (Myr) ago, a period of global warmth
reversed the previous ice growth on Antarctica, leading to the retreat
of the West Antarctic Ice Sheet and the contraction of the East
Antarctic Ice Sheet<sup><a href="http://www.nature.com/ngeo/journal/v5/n8/full/ngeo1498.html#ref1" title="Billups, K. & Schrag, D. P. Paleotemperatures and ice volume of the past 27[thinsp]Myr revisited with paired Mg/Ca and O-18/O-16 measurements on benthic foraminifera. Paleoceanography 17, 1003 (2002)." id="ref-link-13">1</a>, <a href="http://www.nature.com/ngeo/journal/v5/n8/full/ngeo1498.html#ref2" title="Shevenell, A. E., Kennett, J. P. & Lea, D. W. Middle Miocene ice sheet dynamics, deep-sea temperatures, and carbon cycling: A Southern Ocean perspective. Geochem. Geophys. Geosy. 9, Q02006 (2008)." id="ref-link-14">2</a></sup>. Pollen recovered from the Antarctic shelf indicates the presence of substantial vegetation on the margins of Antarctica 15.7<span class="mb"><span class="mb"> </span></span>Myr ago<sup><a href="http://www.nature.com/ngeo/journal/v5/n8/full/ngeo1498.html#ref3" title="Warny, S. et al. Palynomorphs from a sediment core reveal a sudden remarkably warm Antarctica during the middle Miocene. Geology 37, 955-958 (2009)." id="ref-link-15">3</a></sup>.
However, the hydrologic regime that supported this vegetation is
unclear. Here we combine leaf-wax hydrogen isotopes and pollen
assemblages from Ross Sea sediments with model simulations to
reconstruct vegetation, precipitation and temperature in Antarctica
during the middle Miocene. Average leaf-wax stable hydrogen isotope (δD)
values from 20 to 15.5<span class="mb"><span class="mb"> </span></span>Myr
ago translate to average δD values of −50‰ for precipitation at the
margins of Antarctica, higher than modern values. We find that
vegetation persisted from 20 to 15.5<span class="mb"><span class="mb"> </span></span>Myr ago, with peak expansions 16.4 and 15.7<span class="mb"><span class="mb"> </span></span>Myr ago coinciding with peak global warmth<sup><a href="http://www.nature.com/ngeo/journal/v5/n8/full/ngeo1498.html#ref4" title="Zachos, J. C., Pagani, M., Sloan, L., Thomas, E. & Billups, K. Trends, rhythms and aberrations in global climate 65[thinsp]Myr to present. Science 292, 686-692 (2001)." id="ref-link-16">4</a></sup> and vegetation growth<sup><a href="http://www.nature.com/ngeo/journal/v5/n8/full/ngeo1498.html#ref5" title="Diester-Haass, L. et al. Mid-Miocene paleoproductivity in the Atlantic Ocean and implications for the global carbon cycle. Paleoceanography 24, PA1209 (2009)." id="ref-link-17">5</a></sup>. Our model experiments are consistent with a local moisture source in the Southern Ocean<sup><a href="http://www.nature.com/ngeo/journal/v5/n8/full/ngeo1498.html#ref6" title="Lee, J. E., Fung, I., DePaolo, D. J. & Otto-Bliesner, B. Water isotopes during the last glacial maximum: New general circulation model calculations. J. Geophys. Res. 113, D19109 (2008)." id="ref-link-18">6</a></sup>. Combining proxy measurements with climate simulations, we conclude that summer temperatures were about 11<span class="mb"><span class="mb"> </span></span>°C warmer than today, and that there was a substantial increase in moisture delivery to the Antarctic coast.<br>
------------------------------------------------------------------------------------------------<br><a href="http://www.nasa.gov/topics/earth/features/antarctica20120617.html">http://www.nasa.gov/topics/earth/features/antarctica20120617.html</a><br>
<br><div class="name_address"><div class="address"><span class="bold">Study Finds Ancient Warming Greened Antarctica</span></div><div class="promodatepress"><span class="bold">06.17.12</span></div><div style="clear:both">
</div></div>PASADENA, Calif. -- A new university-led study with NASA participation
finds ancient Antarctica was much warmer and wetter than previously
suspected. The climate was suitable to support substantial vegetation --
including stunted trees -- along the edges of the frozen continent.
<p>
The team of scientists involved in the study, published online June 17
in Nature Geoscience, was led by Sarah J. Feakins of 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.
</p><p>
By examining plant leaf wax remnants in sediment core samples taken from
beneath the Ross Ice Shelf, the research team found summer temperatures
along the Antarctic coast 15 to 20 million years ago were 20 degrees
Fahrenheit (11 degrees Celsius) warmer than today, with temperatures
reaching as high as 45 degrees Fahrenheit (7 degrees Celsius).
Precipitation levels also were found to be several times higher than
today.
</p><p>
"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."
</p><p>
Scientists began to suspect that high-latitude temperatures during the
middle Miocene epoch were warmer than previously believed when co-author
Sophie Warny, assistant professor at LSU, discovered large quantities
of pollen and algae in sediment cores taken around Antarctica. Fossils
of plant life in Antarctica are difficult to come by because the
movement of the massive ice sheets covering the landmass grinds and
scrapes away the evidence.
</p><p>
"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.
</p><p>
Tipped off by the tiny pollen samples, Feakins opted to look at the
remnants of leaf wax taken from sediment cores for clues. Leaf wax acts
as a record of climate change by documenting the hydrogen isotope ratios
of the water the plant took up while it was alive.
</p><p>
"Ice cores can only go back about one million years," Feakins said. "Sediment cores allow us to go into 'deep time.'"
</p><p>
Based upon a model 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 created experiments to find out
just how much warmer and wetter climate may have been.
</p><p>
"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."
</p><p>
The peak of this Antarctic greening occurred during the middle Miocene
period, between 16.4 and 15.7 million years ago. This was well after the
age of the dinosaurs, which became extinct 64 million years ago. During
the Miocene epoch, mostly modern-looking animals roamed Earth, such as
three-toed horses, deer, camel and various species of apes. Modern
humans did not appear until 200,000 years ago.
</p><p>
Warm conditions during the middle Miocene are thought to be associated
with carbon dioxide levels of around 400 to 600 parts per million (ppm).
In 2012, carbon dioxide levels have climbed to 393 ppm, the highest
they've been in the past several million years. At the current rate of
increase, atmospheric carbon dioxide levels are on track to reach middle
Miocene levels by the end of this century.
</p><p>
High carbon dioxide levels during the middle Miocene epoch have been documented in
other studies through multiple lines of evidence, including the number of microscopic pores
on the surface of plant leaves and geochemical evidence from soils and marine organisms.
While none of these ‘proxies’ is as reliable as the bubbles of gas trapped in ice cores,
they are the best evidence available this far back in time. While scientists do not yet know
precisely why carbon dioxide was at these levels during the middle Miocene, high
carbon dioxide, together with the global warmth documented from many parts of
the world and now also from the Antarctic region, appear to coincide during this period in
Earth’s history.
</p><p>
This research was funded by the U.S. National Science Foundation with
additional support from NASA. The California Institute of Technology in
Pasadena manages JPL for NASA.
</p><p>
For more information about NASA programs and projects, visit: <a href="http://www.nasa.gov/">http://www.nasa.gov/</a> .
</p>
<div class="space_div">Alan Buis 818-354-0474 <br></div><span class="credits"> Jet Propulsion Laboratory, Pasadena, Calif. <br> <a href="mailto:Alan.buis@jpl.nasa.gov">Alan.buis@jpl.nasa.gov</a> <br><br> J. D. Harrington 202-358-5241<br>
NASA Headquarters, Washington <br> <a href="mailto:j.d.harrington@nasa.gov">j.d.harrington@nasa.gov</a> <br><br> Robert Perkins 213-740-9226<br> University of Southern California, Los Angeles<br> <a href="mailto:perkinsr@usc.edu">perkinsr@usc.edu</a> <br>
<br> Zac Lemoine 225-578-1399<br> Louisiana State University, Baton Rouge<br> <a href="mailto:jlemo26@lsu.edu">jlemo26@lsu.edu</a> <br><br> 2012-179</span><br>------------------------------------------<br>Vision2020 Post: Ted Moffett<br>