Environmental Engineering Reference
In-Depth Information
DID YOU KNOW?
The world's oceans are the primary long-term sink for human-caused CO
2
emissions, currently accounting for a global net uptake of about 2 gigatons
of carbon annually. This uptake is not a result of deliberate sequestration but
instead occurs naturally through chemical reactions between seawater and CO
2
in the atmosphere. The absorption of atmospheric CO
2
causes the oceans to
become more acidic.
Ocean acidification.
(OA) is the term given to the chemi-
cal changes in the ocean as a result of carbon dioxide emissions. Many marine
organisms and ecosystems depend on the formation of carbonate skeletons and
sediments that are vulnerable to dissolution in acidic waters (see Figure 9.3).
Laboratory and field measurements indicate that CO
2
-induced acidification
may eventually cause the rate of dissolution of carbonate to exceed its rate of
formation in these ecosystems. The impacts of ocean acidification and deliber-
ate ocean fertilization on coastal and marine food webs and other resources
are poorly understood. Scientists are studying the effects of oceanic carbon
sequestration on these important environments.
activities undertaken specifically to sequester carbon. The largest net uptake is due
primarily to ongoing natural regrowth of forests that were harvested during the 19th
and early 20th centuries.
Existing terrestrial carbon storage is susceptible to disturbances such as fire, disease,
and change in climate and land use. Boreal forests, also known as
taiga
, and northern
peatlands, which store nearly half the total terrestrial carbon in North American, are
already experiencing substantial warming, resulting in large-scale thawing of perma-
frost and dramatic changes in aquatic and forest ecosystems. USGS scientists have
estimated that at least 10 gigatons of soil carbon in Alaska are stored in organic soils
that are extremely vulnerable to fire and decomposition under warming conditions.
The capacity of terrestrial ecosystems to sequester additional carbon is uncertain.
An upper estimate of potential terrestrial sequestration in the United States might
be the amount of carbon that would be accumulated if U.S. forests and soils were
restored to their historic levels before they were depleted by logging and cultivation.
CO
2-
2 HCO
3
-
CO
2
+
H
2
O
+
Carbon
dioxide
Water
Carbonate
ion
2 Bicarbonate
ions
Consumption of carbonate ions impedes calcification
FIGURE 9.3
Ocean acidification. (From NOAA,
Ocean Acidification: The Other Carbon
Dioxide Problem
, National Oceanic and Atmospheric Administration, Washington, DC,
