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OCR for page 11
The Scientific Questions
CONCEPTUAL MODEL
Conceptual models help to focus assumptions and make key assumptions
explicit They focus research by postulating strong connections andprocesses
that can influence and be influenced by other important processes or out-
comes. They also provide for changing the research enterprise if information
becomes available that leads to a change in the underlying model. To help
focus its assumptions and guide its recommendations to the USGCRP, the
panel developed a conceptual model of global changer (Figure 3-1~. Nothing
in the model appears to conflict with or contradict current USGCRP research
or its interpretations, and we believe that having this model is helpful.
As a means of clarifying the breadth of essential research on global
change, Figure 3-1 gives an overview of human influences on the global
environment. Human actions, which involve factors related to population size
and diskibution as well as economic and social trends, are the point of origin
for a diverse cluster of environmentally potent changes. In Figure 3- I, these
changes are grouped under three broad headings: (1~ land use and land cover;
(2) biogeochemical and hydrologic cycles as well as the introduction and
distribution of potentially harmful substances; and (3) biotic mixing, which
encompasses the transportation of species or genotypes from one region of the
globe to another as well as direct intervention of humans in community
composition through harvesting or management of living communities.
'See somewhat similar models developed by Vitousek et al. ( 1 997a) and Watson
et al. (1998)
11
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OCR for page 13
THE SCIENTIFIC QUESTIONS
13
OCR for page 14
14
GLOBAL CHANGE ECOSYSTEMS RESEARCH
Probably the largest human-caused global effect on marine ecology other
than fishing is (or will be) changes resulting from altered biogeochemical
cycles. At present, very little is known about how those altered cycles affect
the open ocean, and that is one reason that oceans do not constitute a major
part of this report. However, lack of information should not be taken as lack
of any effect, and understanding how altered biogeochemical cycles interact
with the ocean and marine ecosystems is of great practical and scientific
importance.
Inland waters and coastal zones also deserve increased attention. Al-
though they account for only ~ NO of terrestrial surface, and coastal zones are
only a small fraction of the worId's oceans, these environments have an
extraordinarily high collective importance to human well being. Matters
specific to them of global scope include eutrophication, pollution by toxic
chemicals, major physical alterations, and major changes to volumes and flow
rates. These ecosystems are also particularly vulnerable to the effects of
biotic mixing.
Inland and coastal waters are connected to global changes in two ways.
First, they reflect and are linked directly to global changes in terrestrial
environments. For example, land-based changes in land cover, pollution, and
nutrient cycling through human activities have had large effects on aquatic
environments (NRC 2000~. Second, these environments show global com-
monaTities in the ways they respond to specific kinds of human-caused envi-
ronmental changes. For example, inland and coastal waters respond to
enrichment of nutrients in ways that can be generalized on a global scale.
A mature and effective agenda for global change research will include
climate change, and its connections as shown in Figure 3-l, as well as other
components of global change equally important to human interests but not
primarily explained by climate change. The challenge for the immediate
future of this agenda is to add these new elements to research on global
change, and in this way broaden the analysis of global change to match the
full extent of its causes and consequences.
The conceptual model leads to the following general questions:
What do we know about the status and trends of the components
of the model?
By what mechanisms do the connections in the figure operate?
How important is it to understand the mechanisms as opposed only
to the size and direction of the effects?
At what scales are the connections operating?
What are the probable trends in the forcing functions, the primary
factors, and the end points?
What can we learn by knowing the histories of these model com-
OCR for page 15
THE SCIENTIFIC QUESTIONS
.
15
portents, i.e., how their magnitudes and relationships to other
components have changed over time?
Are these trajectories related to the mechanisms, and if so, how?
CRITERIA FOR IDENTIFYING TO QUESTIONS
In evaluating the scientific questions that arise after consideration ofthe
conceptual model, the panel used the following criteria for deciding their
relative importance to the USGCRP.
.
.
How important is each factor that produces environmental effects
in the model? In other words, for each factor, are changes likely
to be global in scale and significant? To what degree and over
what periods are the changes likely to be irreversible?
Are there areas in which understanding ofthe factors in the model
and their effects is impeded by a lack of scientific knowledge?
Would advances in techniques or analysis or new data help us
move beyond our current lack of understanding?
Is there potential for a significant breakthrough in the level and
scope of our scientific understanding if we work on this scientific
question? If we work on this question, are we likely to be able to
make significant progress on other, related scientific questions?
Representative terms from entire chapter:
conceptual model
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