New Research Opportunities in the Earth Sciences - New Research Opportunities in the Earth Sciences - page 76

observatory sites could facilitate comparison and sensitivity studies that might then
serve with reasonable confidence in a broader predictive mode across non-
observatory sites.

Box 2.9
Critical Zone Observatories

The Critical Zone concept, introduced in the 2001 NRC report Basic Research
Opportunities in Earth Science , provides a research framework for the portion of Earth most
closely linked to society and terrestrial life. A network of Critical Zone Observatories (CZOs)
is being established to capitalize on this new research framework by providing locations and
funding mechanisms for integrated, multidisciplinary research. Five observatories are located
in the continental United States and a sixth is in Puerto Rico, and each is in a different
representative landscape. This CZO network is connected to an international network through
collaboration with a parallel effort in the European Union, and data and infrastructure are
open to all researchers. Past studies of the Critical Zone rarely were able to conduct long-
term monitoring efforts. Establishing semi-permanent observatories is allowing long-term
studies to be conducted and has the potential to fill large gaps in our knowledge of Critical
Zone systems. Because human agency plays such a large role in nearly every system of the
Critical Zone, the traditional Earth science objective of constructing a universal model cannot
be accomplished without including the influence of human activities. This is an evolution in
thinking for conventional Earth sciences, but it holds promise of transformative discoveries
that will be both useful to society and add value to the larger corpus of Earth science
understanding. The CZO network is designed to be the mechanism for making those
discoveries.

Responses and Feedbacks of Carbon, Nitrogen, and Water Cycles to Climate
Change

Each year about 120 Pg of carbon is exchanged between the atmosphere and
terrestrial ecosystems through photosynthesis and respiration. This is more than an
order of magnitude larger than estimates of exchange directly due to human activities
(8.7 Pg C/year from fossil fuel combustion and 1.2 P C/year associated with land use
change in 2008; Le Quéré et al., 2009). As a result, global changes in sources and
sinks of carbon due to climate change could be at least as important to global carbon
cycles as the total of all direct anthropogenic fluxes. Indirectly, humans have and
continue to be an important agent of past and future climate change, primarily
through fossil fuel burning. Identification of carbon sources and sinks requires studies
at landscape and regional scales, whereas most research to date on carbon cycling has
been at global (e.g., GCM simulations) or local (e.g., flux tower) scales.
Environments in which climate change could trigger relatively rapid
vegetation and landscape change, such as permafrost areas and wetlands, are of
particular concern to regional and global carbon exchange. For example, there are
23 10 6 km 2 of ice-rich permafrost in the northern hemisphere, more than a third of

which could be actively thawing by 2100, according to model projections (Grosse et
al., 2011). An estimated 1,600 Pg C is stored in the top 3 m of ground in northern
hemisphere permafrost regions (see Figure 2.23). Thawing of permafrost and

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