Page 23 - 全球气候变化及其影响Global Climate Change and Its Impacts-185×260

Chapter 1 Scientific Basis of Global Climate Change

3.Rock Weathering and Sedimentation
The carbon cycle also includes rock weathering and sedimentation processes, which
regulate atmospheric carbon concentrations over geological timescales. For example, weath-
ering of carbonate rocks absorbs atmospheric carbon dioxide, while volcanic eruptions and
tectonic activity release subterranean carbon back into the atmosphere.
The balance of the carbon cycle is crucial for maintaining stable atmospheric carbon
dioxide concentrations. However, since the Industrial Revolution, human activities (e.g., fos-
sil fuel combustion, deforestation, and land-use changes) have significantly increased atmo-
spheric CO levels, leading to global warming and climate change.
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(B) Role of the Nitrogen Cycle
The nitrogen cycle is another vital biogeochemical process that regulates atmospheric
nitrogen forms (e.g., nitrogen gas, ammonia,nitrate, etc.), impacting ecosystem productivity
and the climate system. Nitrogen is essential for plant growth and biological metabolism.
The nitrogen cycle mainly includes these key stages:
【1】Atmosphere-Land Exchange
Atmospheric nitrogen gas (N ) is converted into plant-usable nitrogen compounds (e.g.,
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ammonia and nitrate) through nitrogen fixation (e.g., lightning, industrial fixation, and bio-
logical fixation). Terrestrial ecosystems absorb these nitrogen compounds to support plant
growth and biodiversity.
【2】Nitrogen Mineralization and Denitrification
The mineralization of nitrogen in soil converts organic nitrogen into inorganic nitrogen
for plant uptake; while denitrification transforms inorganic nitrogen back into nitrogen gas
(N ), releasing it into the atmosphere. These processes play a vital role in regulating soil ni-
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trogen levels and ecosystem productivity.
3.Nitrogen’s Oceanic Cycle
The oceanic nitrogen cycle parallels the terrestrial cycle: phytoplankton absorb dis-
solved nitrogen compounds (e.g., nitrate and ammonia) for photosynthesis, while denitrifica-
tion converts nitrogen back into N , returning it to the atmosphere.
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The climate impact of the nitrogen cycle primarily stems from its regulatory role in
ecosystem productivity. For instance, increased nitrogen availability enhances plant growth,
thereby boosting carbon sequestration in terrestrial ecosystems. However, human activities
(e.g., fertilizer use and industrial nitrogen fixation) have drastically altered the nitrogen cy-
cle, causing excessive nitrogen inputs. This has led to environmental issues such as water eu-
trophication, increased greenhouse gas emissions (e.g., nitrous oxide, N O), and ecosystem
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degradation.
（III）Regulatory Role of Biogeochemical Cycles on Climate
Biogeochemical cycles directly influence global climate by regulating the concentration
of greenhouse gases in the atmosphere. The following are key regulatory mechanisms:
1.Carbon Sinks and SourcesRole of
Terrestrial and marine ecosystems regulate atmospheric carbon concentrations by ab-

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