Environmental Engineering Reference
In-Depth Information
6
Beyond the Next Few Centuries
6.1 LONG-TERM FEEDBACKS AND EARTH SYSTEM SENSITIVITY
Earth System Sensitivity: On the Brink of the Anthropocene
Settled agricultural civilization arose during the interglacial period
known as the Holocene, which has extended over the past 10,000 years.
To geologists of the future, the evolution of the present interglacial will look
different from that of the previous major interglacial—the Eemian, which
set in 130,000 years ago. During other interglacials (which have occurred
about every 100,000 years for more than the past 1 million years), CO
2
reached a peak value of about 300 ppm and thereafter began to fall; in this
interglacial, CO
2
will instead rise by an amount that will be determined by
human activities. We are now entering a new geological epoch, called the
Anthropocene, during which the evolution of Earth's environment will be
largely controlled by human activities, notably emissions of carbon dioxide
from deforestation and fossil fuel burning. The Anthropocene will leave an
imprint in the geological record as distinctive as other events that today's
geologists find significant enough to merit a name. Actions taken within this
century will determine whether the Anthropocene climate anomaly repre-
sents a small deviation from the Holocene climate, or a major shift with
a duration of many thousands—perhaps even hundreds of thousands—of
years. Over such long time scales, determining the climate response requires
consideration of Earth System Sensitivity.
Earth System Sensitivity involves a number of processes that are less
well understood than those involved in fast-feedback climate sensitivity or
transient climate response. The challenges are compounded by the slow
nature of these feedbacks, which makes them difficult to study through cur-
rent observations of the changing climate. Study of paleoclimate provides a
window into the operation of these slow processes, but the endeavor there
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