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Chapter II Evidence for Global Climate Change

updates to observation methodologies, and application of statistical models to handlemissing
valuesOr anomalous points. Specifically, regarding discontinuity issues present in historical
data, researchers have developed multiple correction techniques to eliminate artificial bi-
ases caused by factors such as station relocation and instrument replacement. For example,
through combination with other independent observational data (such as satellite remote
sensing and reanalysis products), the reliability and comparability of long-term climate series
can be effectively enhanced.

III. Ocean Temperature and Sea Level Rise

(A) Observational Evidence of Ocean Warming
The ocean has absorbed most of the excess heat caused by increased greenhouse gases,
leading to significant warming of global ocean temperatures over recent decades. Since the
mid-20th century, the average temperature of seawater in the upper 2000-meter depth has
increased by approximately 0.12° per decade.C. This warming trend is particularly evident
in tropical and subtropical seas. For example, some areas of the Pacific and Atlantic Oceans
have already experienced temperature increases exceeding 1°C. Satellite remote sensing
technology and extensive buoy networks provide high-resolution global ocean temperature
distribution maps, helping scientists track and understand this changing process.
Ocean warming accelerates the melting of glaciers and ice sheets, further driving sea
level rise. Warmer seawater intensifies coral reef bleaching, damaging marine biodiversity.
Some fish and other marine organisms are migrating due to altered habitat temperatures,
affecting fishery resource distribution. Extreme weather events such as hurricanes and ty-
phoons may increase in intensity due to rising sea surface temperatures, amplifying disaster
risks in coastal areas.
(II) Observational Evidence of Sea Level Rise
Over the past century, the global average sea level rise rate was approximately 1.4 to
1.8 millimeters per year. However, this rate has accelerated to around 3.6 millimeters per
year during the last 25 years. Thermal expansion refers to the phenomenon where increased
seawater temperature enlarges the distance between water molecules, causing volumetric
expansion and consequently contributing to sea level rise. It is estimated that thermal expan-
sion accounts for nearly half of current sea level rise. On the other hand, melting of land gla-
ciers and ice sheets directly increases water inflow into oceans. Particularly, the ice sheets in
Greenland and Antarctica have shown accelerated melting trends in recent years, becoming
one of the primary sources of future sea level rise. Additionally, local land subsidence may
also exacerbate relative sea level rise in certain regions.
(III) Potential Impacts on Coastal Areas
Rising sea levels make storm surges and high tides more likely to inundate low-lying
areas, increasing flood risks. Some cities along the U.S. East Coast have experienced fre-
quent “sunny-day flooding” in recent years. Higher sea levels mean greater wave energy

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