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托福阅读――气候生态类(一)
智 课 网 托 福 备 考 资 料
托福阅读――气候生态类(一)
Variations in the Climate
One of the most difficult aspects of deciding whether current
climatic events reveal evidence of the impact of human activities
is that it is hard to get a measure of what constitutes the natural
variability of the climate. We know that over the past millennia
the climate has undergone major changes without any significant
human intervention. We also know that the global climate
system is immensely complicated and that everything is in some
way connected, and so the system is capable of fluctuating in
unexpected ways. We need therefore to know how much the
climate can vary of its own accord in order to interpret with
confidence the extent to which recent changes are natural as
opposed to being the result of human activities.
Over long periods of time, substances whose physical and
chemical properties change with the ambient climate at the time
can be deposited in a systematic way to provide a continuous
record of changes in those properties overtime, sometimes for
hundreds or thousands of years. Generally, the layering occurs on
an annual basis, hence the observed changes in the records can
be dated. Information on temperature, rainfall, and other aspects
of the climate that can be inferred from the systematic changes
in properties is usually referred to as proxy data. Proxy
temperature records have been reconstructed from ice core
drilled out of the central Greenland ice cap, calcite shells
embedded in layered lake sediments in Western Europe, ocean
floor sediment cores from the tropical Atlantic Ocean, ice cores
from Peruvian glaciers, and ice cores from eastern Antarctica.
While these records provide broadly consistent indications that
temperature variations can occur on a global scale, there are
nonetheless some intriguing differences, which suggest that the
pattern of temperature variations in regional climates can also
differ significan
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