Page 12 - 全球气候变化及其影响Global Climate Change and Its Impacts-185×260

Global Climate Change and Its Impacts

in the aforementioned domains and its significance for global climate change.
The ocean, as the largest thermal reservoir on Earth, plays a crucial role in maintaining
global energy balance. It absorbs approximately 50% to 90% of solar radiation energy and
redistributes it through complex ocean current systems. This thermal redistribution mitigates
the temperature gradient between the equator and polar regions, thereby stabilizing global
climate patterns. For instance, the Gulf Stream in the North Atlantic transports warm surface
waters from tropical zones to high-latitude areas, resulting in relatively mild climates along
Western European coastlines. Additionally, deep ocean circulation significantly contributes
by carrying cold, salty deep waters that sink and ultimately mix with surface waters, forming
a complete heat exchange cycle. This heat transfer mechanism ensures relative stability in
Earth’s surface temperatures and exerts substantial influence on the long-term evolution of
the global climate system.
Changes in ocean salinity also have significant impacts on climate. Seawater salinity
directly affects its density, thereby controlling the dynamics of deep-water currents. When
sea ice forms, it releases salt, increasing the salinity of surrounding seawater; conversely,
when sea ice melts, it dilutes seawater and reduces salinity. These salinity variations can
alter ocean circulation patterns, particularly the Atlantic Meridional Overturning Circula-
tion (AMOC) - a global conveyor belt connecting northward-flowing warm surface waters
with southward-returning cold deep waters. If AMOC weakens or collapses, it could trigger
abrupt temperature declines in the Northern Hemisphere, as evidenced in some paleoclimate
records. Furthermore, salinity changes affect marine ecosystem health, as many marine or-
ganisms depend on specific salinity environments. Any significant alterations could disrupt
entire ecosystems, indirectly influencing the climate system.
The ocean participates in a series of complex biogeochemical cycles, with the carbon
cycle being the most prominent. The ocean absorbs a substantial amount of carbon dioxide
(CO ), accounting for approximately one-quarter of human-induced emissions. This pro-
2
cess primarily occurs in the upper ocean through two pathways: physical dissolution and
photosynthesis. Phytoplankton fix CO through photosynthesis to produce organic matter,
2
with a portion sinking to the deep sea as part of sediments, forming the so-called “biolog-
ical pump.” Meanwhile, below the carbonate compensation depth (CCD) in the ocean, the
decomposition of calcareous shells releases CO back into the water, forming a natural feed-
2
back mechanism. In addition to the carbon cycle, other nutrient elements such as nitrogen
and phosphorus also cycle within the ocean, supporting abundant marine life and indirectly
influencing the climate system—for example, by altering cloud cover and albedo to regulate
Earth’s energy balance. Thus, the ocean’s biogeochemical cycles not only constitute a vital
component of the global carbon cycle but also serve as one of the key factors in maintaining
Earth’s climatic stability.

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