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Global Climate Change and Its Impacts

II. Causes and Manifestations of Climate Change Irreversibility

Within the intricate scenario of global climate change, the irreversibility of climate
change has become a focal point of high concern for both the scientific community and
various sectors of society. This characteristic profoundly influences the future trajectory of
Earth’s ecosystems and human societies, rooted in multiple complex causes and manifested
in diverse forms within the climate system.
From the perspective of causation, the breaching of ecosystem thresholds constitutes
one of the key factors leading to irreversible climate change. Many ecosystems possess spe-
cific thresholds, and when external disturbances (primarily stemming from climate change)
exceed these limits, the ecosystem will undergo irreversible transformations. Taking the Arc-
tic sea ice ecosystem as an example, sea ice exhibits extreme sensitivity to temperature vari-
ations. With persistent global warming and rising temperatures in the Arctic region, sea ice
coverage continues to diminish. When the sea ice area decreases beyond a critical point that
surpasses the threshold required for ecosystem stability maintenance, a series of irreversible
changes ensue. Sea ice possesses high albedo properties that reflect substantial solar radi-
ation, thereby maintaining Earth’s energy balance. Following ice reduction, the previously
reflected solar radiation becomes absorbed by darker ocean surfaces, leading to further sea-
water temperature increases that accelerate ice melt and establish a positive feedback loop.
Once this vicious cycle initiates, even with effective future control of global greenhouse gas
emissions, sea ice recovery to its original scale and state becomes improbable in the short
term, consequently exerting persistent and difficult-to-reverse impacts on the global climate
system.
The triggering of Earth system feedback mechanisms also constitutes a significant cause
of climate change irreversibility. Within the Earth system, there exist numerous interconnect-
ed feedback mechanisms, among which the carbon cycle feedback mechanism is particularly
critical. As the concentration of greenhouse gases such as carbon dioxide in the atmosphere
increases, global temperatures rise. This temperature elevation drives terrestrial and marine
ecosystemsto undergochanges. For instance, on land, rising temperatures accelerate the
decomposition of soil organic matter, releasing more carbon dioxide into the atmosphere;
in the ocean, seawater warming enhances marine organism respiration while reducing the
ocean’s carbon dioxide absorption capacity, thereby decreasing its carbon dioxide absorp-
tion efficiency. These changes further increase atmospheric carbon dioxide concentrations,
exacerbate global warming, and form a positive feedback mechanism. Once such feedback
mechanisms areintensely triggered, even if greenhouse gas emissions are reduced, due to the
altered ecosystems, their source- sink relationshipwith carbon dioxide cannot be restored in
the short term, rendering the climate change trend difficult to reverse.
In the climate system, the irreversibility of climate change manifests prominently. From
the perspective of temperature changes, the global average temperature continues to rise and
will struggle to return to pre-industrial levels for a considerable period. Numerous studies

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