Global Change: the Role of Marine Geology
211
ment"? This cannot be answered. Perhaps (just perhaps) this event was so unusually
severe because (a) it would have been strong in any case (b) it was reinforced by
effects from a volcanic eruption (El Chich6n, in Mexico) (c) it occurred within the
warmest decade on record. Which brings us back to the original question about the
unusualness of the 1980s. More will be learned as we study longer records.
7.7.4 The Coral Record. Wherever there are corals in the tropical oceans, there is a
record of climatic change within the skeletons of these small colonial organisms (Fig.
6.8). These records are now being actively collected, from Bermuda, the Galapagos,
Fanning Island, the Great Barrier Reef, and other places. There are two pieces of
information that are especially useful: rate of growth and oxygen isotope composition. There may be other types of useful indices as well, related to biomarkers and
trace elements deposited within the skeleton - research on these has just recently
started.
Time resolution is in some cases being pushed toward daily fluctuations. The
layers representing daily growth are typically less than 20 J.Ull thick. The measurement of daily growth rates should greatly expand the use of corals as indicators of
environmental change.
7.7.5 Global Change: the Role of Marine Geology. "Global change" has become
the catch phrase expressing the notion that human industrial activities are impacting
the planetary environment in major ways, with important consequences for the future
of global climate. The health and wealth of nations depend largely on climate, as
becomes obvious especially during long spells of drought. Thus, any long-lasting
significant changes in weather patterns are of prime concern. At present, greenhouse
gases (carbon dioxide and methane, among others) are added to the atmosphere in
substantial amounts that increase from one year to the next. Extrapolating into the
future, computer modeling of the radiation balance of the Earth suggests that a
doubling of carbon dioxide over the natural background (expected within the next 50
years or so) should increase global temperatures by some 3 °C with an uncertainty of
about 1.5 DC. High latitudes are expected to be much more affected than low latitudes.
There is some evidence that the expected global warming has, in fact, begun: the
last decade was the warmest on record since global records have been kept (about the
last 100 to 150 years) (see Fig. 7.16). Clearly, an important question is whether this
recent increase in global temperatures could be just a chance occurrence, unrelated to
human activities. To check this possibility we need "climate proxies" that allow us to
determine past fluctuations in wheather patterns. Also, once we are able to establish
the amplitude of natural fluctuations (before the industrial revolution), we should be
able to improve the computer models: to be trustworthy, these should generate climate predictions that are tagged with the appropriate uncertainties.
Climate proxies can be derived from a great variety of high-resolution records,
such as tree rings, ice cores, and cave deposits. In marine geology, coral growth
bands (Sect. 7.4) and varved sediments are of special importance in this context
(Sect. 3.9).
211
ment"? This cannot be answered. Perhaps (just perhaps) this event was so unusually
severe because (a) it would have been strong in any case (b) it was reinforced by
effects from a volcanic eruption (El Chich6n, in Mexico) (c) it occurred within the
warmest decade on record. Which brings us back to the original question about the
unusualness of the 1980s. More will be learned as we study longer records.
7.7.4 The Coral Record. Wherever there are corals in the tropical oceans, there is a
record of climatic change within the skeletons of these small colonial organisms (Fig.
6.8). These records are now being actively collected, from Bermuda, the Galapagos,
Fanning Island, the Great Barrier Reef, and other places. There are two pieces of
information that are especially useful: rate of growth and oxygen isotope composition. There may be other types of useful indices as well, related to biomarkers and
trace elements deposited within the skeleton - research on these has just recently
started.
Time resolution is in some cases being pushed toward daily fluctuations. The
layers representing daily growth are typically less than 20 J.Ull thick. The measurement of daily growth rates should greatly expand the use of corals as indicators of
environmental change.
7.7.5 Global Change: the Role of Marine Geology. "Global change" has become
the catch phrase expressing the notion that human industrial activities are impacting
the planetary environment in major ways, with important consequences for the future
of global climate. The health and wealth of nations depend largely on climate, as
becomes obvious especially during long spells of drought. Thus, any long-lasting
significant changes in weather patterns are of prime concern. At present, greenhouse
gases (carbon dioxide and methane, among others) are added to the atmosphere in
substantial amounts that increase from one year to the next. Extrapolating into the
future, computer modeling of the radiation balance of the Earth suggests that a
doubling of carbon dioxide over the natural background (expected within the next 50
years or so) should increase global temperatures by some 3 °C with an uncertainty of
about 1.5 DC. High latitudes are expected to be much more affected than low latitudes.
There is some evidence that the expected global warming has, in fact, begun: the
last decade was the warmest on record since global records have been kept (about the
last 100 to 150 years) (see Fig. 7.16). Clearly, an important question is whether this
recent increase in global temperatures could be just a chance occurrence, unrelated to
human activities. To check this possibility we need "climate proxies" that allow us to
determine past fluctuations in wheather patterns. Also, once we are able to establish
the amplitude of natural fluctuations (before the industrial revolution), we should be
able to improve the computer models: to be trustworthy, these should generate climate predictions that are tagged with the appropriate uncertainties.
Climate proxies can be derived from a great variety of high-resolution records,
such as tree rings, ice cores, and cave deposits. In marine geology, coral growth
bands (Sect. 7.4) and varved sediments are of special importance in this context
(Sect. 3.9).