New Research Opportunities in the Earth Sciences - New Research Opportunities in the Earth Sciences - page 81

of legumes are currently adding more new reactive nitrogen to the environment than
natural terrestrial processes. Impacts of reactive nitrogen on the environment are
exacerbated by its cascading effect as it moves through the environment, such that
each molecule of nitrogen can contribute to multiple environmental problems. Future
population increases, and improvements in standards of living, will likely add to this
anthropogenic nitrogen load through growing use of energy, additional demand for
food production, and improvements in diet. Policies and practices for nitrogen use
must balance the excesses and inefficiencies associated with nitrogen use in much of
the developed world with the need for food in other parts of the world (Galloway et
al., 2008).
Understanding these and other anthropogenic impacts on the environment
requires integrated, interdisciplinary studies of climate, biogeochemical cycles, water,
ecosystems, and humans. In particular, it is important that Earth scientists identify
processes and thresholds that, when crossed, would lead to irreversible and
unacceptable environmental change. Rockström et al. (2009) suggest that this
threshold has already been crossed with respect to atmospheric carbon dioxide, the
nitrogen cycle, and biodiversity loss (see Figure 2.25).
Figure 2.25 Earth-system processes and their proximity to crossing threshold
conditions that lead to unacceptable environmental change. Processes are indicated
outside each sector. Green colors denote safe operating conditions. The heights of the
red-colored wedges represent the status of each process with respect to safe operating
conditions. In this figure, climate change, the nitrogen cycle, and biodiversity loss
have crossed the threshold of unacceptable environmental change. SOURCE:
Rockström et al. (2009). Reprinted by permission from Macmillan Publishers Ltd.