4. Read the passage below and choose the best
answer to the question.
past climate--including temperature and elements in the atmosphere--has
recently been studied by analyzing ice samples from Greenland and Antartica.
The air bubbles in the ice have shown that, over the past 160,000 years,
there has been a close correlation between temperature changes and level
of natural greenhouse gases carbon dioxide and methane. One recent analysis
from Greenland showed that at the end of the last glacial period (when
the great ice sheets began to retreat to their present position), temperatures
in southern Greenland rose from 5 to 7 degrees in about 100 years.
are not the only method of determining characteristics of the Earth's
ancient climate history. Analysis of dust layers from ancient volcanic
activity is another such method; as is the study of ice cores, which
interpret past solar activity that may have affected our climate.
passage states that: