57
The Medieval Warm Period (MWP) lasted from about a.d.
900 to 1300. Although its cause is not yet well understood, it seems to
be related to a strengthening of Atlantic meridional overturning. The
MWP was a time of relatively warm, dry temperatures (although it is
worth noting that temperatures during the MWP were never as high
as during the 1990s). In Europe, crops thrived, and the people were
Lonnie Thompson: Constructing Earth’s Climate
from the World’s High Peaks
Lonnie Thompson’s life began far from
the tropical mountain peaks where he
now spends much of his time. As a boy
on a farm in rural West Virginia, he was
fascinated with meteorology. He attended
Marshall College, where he studied to
become a coal geologist. Thompson mar-
ried the only woman studying physics at
M
arshall, Ellen Mosely, and the couple
moved to Ohio State University for gradu-
ate school. Thompson’s life took a fateful
turn when he secured a research job work-
ing with the first ice cores ever collected.
The young geologist was entranced by the
immense possibilities that ice cores held
for the reconstruction of past climate and
was inspired to switch his studies to glaci-
ology. After one field season in Antarctica,
Thompson decided to study tropical moun-
tain glaciers, ignoring the prevailing idea
that mountain glaciers were too active to
contain a usable climate history. In 1974,
he became the first scientist to drill a
mountain glacier, the Quelccaya ice cap,
at an elevation of 18,600 feet (5,670 m) in
the Peruvian Andes, and he has worked on
mountain glaciers ever since.
Gathering ice on tropical mountain
glaciers presents unique difficulties.
Tropical mountain glaciers are at very
high altitudes. At those heights, people
are susceptible to acute mountain sick-
ness, pulmonary edema, frostbite, and
other ills, all of which have plagued mem-
bers of Thompson’s ice coring team. The
sample sites are inaccessible to aircraft
and other vehicles, so people (sometimes
with the help of yaks) must maneuver six
tons (5.4 metric tons) of equipment over
the jagged and crevassed glacial sur-
face, while avoiding avalanches, altitude
sickness, frigid temperatures, and wind-
s
torms. Cores are retrieved in one-meter
sections and stored in insulated boxes.
When drilling is complete, about four tons
(3.6 metric tons) of cores must be quickly
carried down the mountain, transported
overland, and then placed aboard an air-
plane. These cores must be shipped to the
OSU center before they melt. Once they
reach the research center, they are stored
in refrigerated vaults that are maintained
at Arctic temperatures of -22°F (-30°C).
Thompson braves these adverse con-
ditions because of the important story
that tropical mountain glaciers have to tell
about regional climate and environmental
change. Tropical glaciers contain a thor-
ough record of El Niño events and, he says,
understanding the natural variability of
these natural climate events is essential
for assessing the degree to which human
activities are now inducing climate change.
Tropical regions are also extremely sensi-
tive to greenhouse gas levels: If rising CO
2
causes tropical oceans to evaporate, the
added water vapor will raise atmospheric
greenhouse gas levels even higher and
increase global temperatures.
Thompson is now the world’s foremost
expert in the study of paleoclimate using
ice cores from mountain glaciers. Over
the past 30 years, he has led more than
5
0 expeditions to 11 high-elevation ice
fields on 5 continents. He has cored about
23,000 feet (7,000 m) of ice reaching as
far back in time as 750,000 years. The
scientist is now in a race against time to
gather as many ice cores as he can before
the ice record melts away. He estimates
that the Peruvian Andes, which contain
the world’s largest concentration of tropi-
cal glaciers, have lost about 20% of their
mass since 1972. For example, in the years
1991–2005, Qori Kalis glacier retreated
about 10 times faster (200 feet [61 m] per
year) than during the years from 1963 to
1978 (20 feet [6.1 m] per year).
As Thompson stated in Ohio State
Research in 2006, “What this [research] is
really telling us is that our climate system
is sensitive, it can change abruptly due
to either natural or to human forces. If
what happened 5,000 years ago were to
h
appen today, it would have far-reaching
social and economic implications for the
e
ntire planet. The take-home message is
that global climate can change abruptly,
and with 6.5 billion people inhabiting the
planet, that’s serious.”
Climate Change through earth History