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The world's glaciers contain the history of climate change over many thousands of years. By studying this record, scientists can identify the natural cycles in global warming and cooling. Vertical cores drilled through several thousand feet of ice provide a sample of all the layers of snow that have accumulated over thousands of years. Some of the deepest cores have been drilled in Greenland and east Antarctica. The Greenland Ice Sheet Project Two drilled to a depth of 10,000 feet (3,050 m) representing over 110,000 years of environmental record. Scientists working at the Russian Antarctic base at Vostok have recently completed drilling and obtained the longest record of climate and atmospheric history: 420,000 years! How do scientists draw their conclusions from ice core records? Find out! |
The mechanisms that trigger an ice age or an extended period of global warming are the subject of much research and debate. Scientists have identified a complicated mix of interacting variables that appear to influence long-term climate trends. Three such factors that are thought to control climate are solar radiation, the presence of atmospheric dust, and the chemical composition of the atmosphere.
Solar Radiation
Radiation from the sun that is received at the top of the
atmosphere is called insolation and it varies over time. As the earth
moves closer to the sun, insolation increases; as it moves further
away, insolation decreases. These changes in insolation were studied
by Serbian astronomer Milutin Milankovitch (1879-1954) who wondered
whether the development of an ice age was related to changes in the
earth's orbit. He found that the earth's orbit is elliptical and
varies widely during a 100,000 year cycle; that the earth's axis
"wobbles" on a 26,000 year cycle; and that the tilt of the earth
changes every 40,000 years. These changes are called Milankovitch
cycles and account for some of the changes in past climates.
Atmospheric Dust
Volcanic eruptions and erosion from the earth's surface put dust
and other fine particles of matter into the atmosphere. The presence
of dust in the atmosphere prevents solar radiation from reaching the
surface of the earth which causes the atmosphere to cool. This
cooling, in turn, may inhibit vegetation growth which creates more
exposed land susceptible to erosion. Ice core researchers look for
the presence of calcium dust in the ice when they reconstruct ancient
climates. Calcium comes from limestone which is deposited in the
ocean in large quantities. During ice ages, sea level decreases as
water is trapped in ice sheets around the globe. This exposes the
continental shelves rich in calcium and prone to erosion. The dust is
blown into the atmosphere and eventually falls to earth with rain or
snow, preserving it as a record within the ice.
Atmospheric Gases
Some gases accentuate the warming or cooling of the atmosphere.
Those that warm the atmosphere are called greenhouse gases. These
include water vapor, carbon dioxide, and methane. Gasses that are
present in the atmosphere fall to earth with snow and fill the air
spaces between the snowflakes on the ground. As the snow accumulates
over time and turns to ice, the gas is trapped in small bubbles.
These bubbles can be sampled using sophisticated equipment to tell us
which gases were present in the atmosphere when that ice was formed
and therefore what the climate was like.
The scientists on this expedition will be looking only at the last 200 years of ice core history. They are interested in learning what the ice records about human influences on the earth's climate and Antarctica's environment.
