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Chapter II Evidence for Global Climate Change

ferent phases, which can be categorized into low-magnitude variation phase and high-mag-
nitude variation phase. During the low-magnitude variation phase, the fluctuation range of
climatic variables remains relatively narrow, exerting limited impacts on ecosystems and
human societies. Throughout Earth’s extensive history, there existed specific periods when
climate maintained relative stability, with temperature and precipitation fluctuations confined
to a small range. Taking the Holocene Climatic Optimum approximately 5,000 to 3,000
years ago as an example, this period was characterized by relatively warm and humid global
climate conditions withminimal climatic variability. The stable and favorable climatic con-
ditions provided exceptionally advantageous environments for crop growth, enabling agri-
cultural civilizations to flourish in numerous regions. During this period, early agricultural
settlements gradually formed, humans began domesticating more plant and animal species,
and agricultural production technologies achieved preliminary development.
The phase of substantial changes is characterized by climatic variables undergoing ex-
tremely pronounced and substantial fluctuations within short timeframes. This substantial
change process is often accompanied by a series of abrupt climatic events, exerting profound
and far-reaching impacts on both ecosystems and human societies. The LastGlacial Period
transition toThe transition to the Holocene represents a highly representative phase of sig-
nificant climate change. During this critical period, global temperatures exhibited a rapid
upward trend with temperature increases reaching several degrees Celsius, accompanied by
substantial sea-level rise and rapid retreat of numerous glaciers and ice sheets. This dramatic
climate shift directly triggered large-scale reorganization of global ecosystems, fundamen-
tally altering the geographical distribution ranges of many species. Species adapted to cold
environments gradually faced extinction due to their inability to quickly adapt to rapidly
warming conditions, while warmth-adapted species expanded extensively. In terms of human
societal development, this period also witnessed major transformations as humans transi-
tioned from predominantly hunter-gatherer lifestyles to agricultural settlement patterns. The
emergence of agriculture laid a solid foundation for the development of human civilization,
enabling the establishment of more stable communities and the evolution of early social di-
visions of labor and culture.
The degree of impact can also serve as a crucial criterion for dividing climate change
phases, specifically categorized into phases of lesser impact and phases of greater impact.
During phases of lesser impact, the effects of climate change on ecosystems and human
societies remain relatively mild. Ecosystems possess inherent regulatory mechanisms that
enable partial adaptation to climate-induced changes, while human societies can employ rou-
tine adjustment measures—such as altering crop planting schedules or modifying irrigation
methods—to effectively respond to climatic shifts. For instance, in some regions, gradual
climate changes may lead to subtle modifications in crop varieties cultivated, transitioning
from temperature-sensitive species to varieties with greater temperature adaptability. Species
within ecosystems may address environmental pressures either by migrating to more suitable

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