Page 509 - Environment: The Science Behind the Stories

THE SCIENCE BEHIND THE STORY

Reading History in
the World’s Longest
Ice Core

In the most frigid reaches of our planet,
snow falling year after year for millennia
compresses into ice and stacks up into
immense sheets that scientists can mine
for clues to Earth’s climate history. The
ice sheets of Antarctica and Greenland
trap tiny air bubbles, dust particles, and
other proxy indicators (p. 507) of past
conditions. By drilling boreholes and
extracting ice cores, researchers can
tap into these valuable archives.
Recently, researchers drilled and an ePica researcher prepares a dome c ice core sample for analysis.
analyzed the deepest core ever. At a
remote and pristine site in Antarctica
named Dome C, they drilled down Dome C, a high summit of the cover all 800,000 years. By analyz-
3270 m (10,728 ft) to bedrock and Antarctic ice sheet, is one of the coldest ing air bubbles trapped in the ice, the
pulled out more than 800,000 years’ spots on the planet, with an annual researchers quantified atmospheric
worth of ice. The longest previous ice mean temperature of –54.5°C (–98.1°F). concentrations of carbon dioxide
core (from Antarctica’s Vostok station) The Dome C ice core was drilled by and methane (red line and green line,
had gone back “only” 420,000 years. the European Project for Ice Coring respectively, in Figure 1).
Ice near the top of these cores in Antarctica (EPICA), a consortium of These data show that by emit-
was laid down most recently, and ice researchers from 10 European nations. ting these greenhouse gases since the
at the bottom is oldest, so by analyz- In 2004, this team of 56 research- industrial revolution, we have brought
ing ice at intervals along the core’s ers published a paper in the journal their atmospheric concentrations well
length, researchers can generate a Nature, reporting data across 740,000 above the highest levels they reached
timeline of environmental change. To years. The researchers obtained data naturally any time in the last 800,000
date layers of the ice core, researchers on surface air temperature by measur- years. Today’s carbon dioxide spike is
first analyze deuterium isotopes (p. 43) ing the ratio of deuterium isotopes to too recent to show up in the ice core,
to determine the rate of ice accumula- normal hydrogen in the ice, because but its concentration (of 396 ppm in
tion, referencing studies and models this ratio is temperature-dependent. 2013) is far above previous maximum
of how ice compacts over time. They From 2005 to 2008, five follow- values (of ~300 ppm) shown in the red
then calibrate the timeline by match- up papers in the journals Science line of the figure. These data reveal that
ing recent events in the chronology (for and Nature reported analyses of we as a society have brought ourselves
example, major volcanic eruptions) with greenhouse gas concentrations from deep into uncharted territory.
independent data sets from previous the EPICA ice core and extended the The EPICA results also confirm
cores, tree rings, and other sources. gas and temperature data back to that temperature swings in the past

mountain. These data show that atmospheric CO concentra- Accurate records of all these types extend back, at most, a
2
tions have increased from 315 ppm in 1958 to 396 ppm in few hundred years.
2013 (Figure 18.7).
Direct measurements of climate variables such as tem- Models help us predict the future
perature and precipitation extend back in time somewhat
further. Precise and reliable thermometer measurements To understand how climate systems function and to predict
cover more than a century. Scientists can also infer past cli- future climate change, scientists simulate climate processes
mate conditions from historical records of economic activi- with sophisticated computer programs. Climate models are
ties affected by climate. Fishers have recorded the timing programs that combine what is known about atmospheric
of sea ice formation, and winemakers have kept meticulous circulation, ocean circulation, atmosphere–ocean interac-
508 records of precipitation and the length of the growing season. tions, and feedback cycles to simulate climate processes

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