Environmental Engineering Reference
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as methane, black carbon on ice/snow, and aerosols can affect the global
warming of coming decades but have little effect on the lock-in to longer-
term warming of Earth over centuries and millennia; that commitment is
primarily controlled by carbon dioxide. {2.1, 2.2, 2.3, 3.4}
Earth is now entering a new geological epoch, sometimes called the An-
thropocene, during which the evolution of the planet's environment will
be largely controlled by the effects of human activities, notably emis-
sions of carbon dioxide. Actions taken during this century will determine
whether the Anthropocene climate anomaly will be a relatively short-term
and minor deviation from the Holocene climate, or an extreme deviation
extending over many thousands of years.
Higher cumulative carbon emissions result in both a higher peak warm-
ing and a longer duration of the warming (see Figure S.4). The duration of the
warming is critical, because an extended period of warming provides more
time for the components of the Earth system that may respond very slowly
(such as the deep oceans and the great ice sheets) to assert themselves, even
very long after anthropogenic emissions have ceased. {6.1}
The sea level rise implications of the Anthropocene could lead to major
changes in the geography of the Earth over the coming millennia. Model
studies suggest that a cumulative carbon emission of about 1,000 to 3,000
GtC would lead to eventual sea level rise due to thermal expansion and
glacier and small ice cap loss alone of the order of 1 to 4 meters. Addi-
tional contributions from Greenland could contribute as much as a further
4 to 7.5 m on multi-millennial time scales, for a possible total of order 5
to 11.5 meters from thermal expansion, glaciers and small ice caps, and
Greenland.
Widespread coastal inundation would be expected if anthropogenic
warming of several degrees is sustained for millennia; although these slow
changes allow time for adaptation, they are essentially irreversible. The pro-
jected fragility of the Greenland ice sheet is in accord with studies suggesting
that Greenland was essentially free of ice during the Pliocene era (which was
probably about 3°C warmer than pre-industrial times in the mid-Pliocene,
about 3-3.3 million years ago). Changes in Antarctica are less clear, in part
because both the West and East Antarctic ice sheets must be considered:
one study suggests that cumulative carbon emission of about 2,000-5,000
GtC could also contribute up to 5 meters of additional sea level rise from
West Antarctic ice sheet loss. Future changes in East Antarctica could offset
at least part of West Antarctic changes. While carbon emissions in the 21st
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