Page 47 - 全球气候变化及其影响Global Climate Change and Its Impacts-185×260

Chapter II Evidence for Global Climate Change

of atmospheric gases, particulates, and chemical substances. The air bubbles in ice cores are
gas samples sealed from the atmosphere when the ice layers formed, containing greenhouse
gases such as carbon dioxide (CO ), methane (CH ), and nitrogen oxides (NOₓ). The concen-
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tration changes of these gases reflect the evolution of past atmospheric composition. Addi-
tionally, chemical components in ice cores like sulfates, nitrates, and organic carbon record
atmospheric impacts from events such as volcanic activity, forest fires, and human activities.
The bubbles in ice cores are key evidence for studying past atmospheric composition.
By comparing the gas concentrations in these bubbles with those in the modern atmosphere,
we can reveal the changing trends in atmospheric composition over time. For example, data
from Antarctic ice core bubbles show that atmospheric carbon dioxide (CO ) concentra-
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tion was approximately 280 ppm (parts per million) before the Industrial Revolution, while
modern atmospheric CO concentration has exceeded 410 ppm. This significant increase is
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primarily attributed to human activities such as fossil fuel combustion and deforestation.
Methane (CH ) concentrations in ice cores also demonstrate a similar trend, with pre-indus-
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trial levels around 700 ppb (parts per billion), compared to modern methane concentrations
exceeding 1800 ppb. These data indicate that human-induced alterations to atmospheric
composition are both substantial and persistent.
In addition to gases trapped in bubbles, the chemical composition in ice cores also pro-
vides crucial clues for studying past climate changes. For example, sulfates and nitrates in
ice cores are typically associated with volcanic activity. Volcanic eruptions release sulfides
and nitrogen oxides that form aerosols in the atmosphere, which settle onto ice sheet surfac-
es through precipitation, creating sulfate and nitrate deposits. By analyzing concentration
changes of sulfates and nitrates in ice cores, we can reconstruct historical volcanic activity
and further understand its impact on climate. Additionally, organic carbon content in ice
cores correlates with forest fires. Carbon particles released by forest fires settle onto ice sheet
surfaces through atmospheric deposition, forming organic carbon deposits. Through analysis
of organic carbon concentration variations in ice cores, we can reconstruct historical forest
fire events and better comprehend their climatic impacts.
Isotope analysis in ice cores is a crucial method for studying past temperature chang-
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es. The oxygen isotope ( O/ O) and hydrogen isotope (D/H) ratios in ice cores are closely
related to temperature. During ice layer formation, the oxygen and hydrogen isotope ratios
in water molecules vary with temperature changes. Generally, higher temperatures corre-
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spond to higher O/ O and D/H ratios in ice cores, while lower temperatures result in lower
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ratios. By analyzing changes in isotope ratios within ice cores, researchers can reconstruct
historical temperature variations. For example, isotopic data from Greenland ice cores indi-
cate that temperatures during the Last Glacial Maximum (approximately 20,000 years ago)
were about 10°C lower than modern temperatures, while interglacial periods were about 2°C
warmer than modern temperatures. These data provide critical evidence for understanding
the alternation between glacial and interglacial periods.

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