Page 20 - 全球气候变化及其影响Global Climate Change and Its Impacts-185×260

Global Climate Change and Its Impacts

cial periods; whereas when Northern Hemisphere summer aligns with aphelion, reduced so-
lar radiation may lead to ice age formation. Precession also interacts closely with variations
in Earth’s axial tilt (the angle between Earth’s rotation axis and its orbital plane), further
influencing long-term global climate evolution.
The Milankovitch cycles have profoundly influenced global climate through variations
in Earth’s orbital parameters. These cyclical variations collectively influence the Earth’s so-
lar radiation receipt, thereby driving long-term climatic evolution. For instance, during the
Quaternary Ice Age, changes in Earth’s orbital parameters were recognized as crucial drivers
for the alternating glacial and interglacial periods. Specifically: eccentricity variations alter
global temperature distribution by modifying solar radiation received at perihelion and aph-
elion; axial tilt variations affect polar temperature changes by shifting the solar declination
range; precession changes impact seasonal climate patterns globally by adjusting solar radia-
tion distribution across different seasons.
The study of Milankovitch cycles not only reveals the long-term evolution patterns of
Earth’s climate but also provides crucial evidence for predicting future climate changes. For
instance, Earth is currently in a period of low eccentricity, small axial tilt, and a precessional
cycle approaching the alignment of Northern Hemisphere summer with aphelion, which may
lead to a more stable global climate and could potentially trigger a new glacial period. How-
ever, greenhouse gas emissions caused by human activities (such as fossil fuel combustion
and deforestation) have significantly accelerated global warming, which may have counter-
acted the climatic driving effects of Milankovitch cycles. Therefore, future research should
further investigate the synergistic effects of Milankovitch cycles and human activities on
global climate change to provide scientific foundations for climate change mitigation.

IV. Internal Variability of the Atmosphere and Oceans

The internal variability of the atmospheric and oceanic systems is a non-negligible and
vital component of the climate system, triggering short-to-medium-term climate variations
through complex interactions. While these internal fluctuations are not the fundamental driv-
ers of long-term climate change, they significantly influence seasonal and annual climate
predictions. Among them, the El Niño-Southern Oscillation (ENSO) phenomenon is one of
the most prominent internal variabilities, while multi-decadal oscillations like the Pacific
Decadal Oscillation (PDO) and the North Atlantic Oscillation (NAO) also profoundly impact
regional and even global climate conditions.
(1) El Niño-Southern Oscillation (ENSO) Phenomenon
The El Niño-Southern Oscillation (ENSO) is a central phenomenon of sea surface tem-
perature anomalies in the Pacific region, characterized by the alternating occurrence of El
Niño and La Niñaevents. El Niño events typically manifest as abnormally high sea surface
temperatures in the central and eastern equatorial Pacific, while La Niñaevents are character-
ized by abnormally low sea surface temperatures. These two phenomena significantly influ-

• 12 •