New Research Opportunities in the Earth Sciences - New Research Opportunities in the Earth Sciences - page 55

How Have the Dynamics of the Global Climate System Varied in the Past?
Contemporary climate change can be better understood through exploration of
the range of climate states, rates, feedbacks, and tipping points captured over Earth's
history. The current glacial state provides an important baseline against which future
climate change can be assessed. Understanding a world characterized by ice sheets at
both poles and atmospheric carbon dioxide partial pressure ( p CO 2 ) up to 30 percent
less than present-day levels, however, captures only a small part of known climate
variability. At current rates of concentration, by the year 2100 greenhouse gas
concentrations will approach atmospheric values inferred for the greenhouse climates
of the Paleogene (Kiehl, 2011; NRC, 2011a). Critical insights into how the Earth's
systems have functioned in such a high CO 2 environment are archived in the records
of past warm periods and major climate transitions. For example, deep-time studies
reveal past periods of anomalous tropical and polar warmth that were associated with
major changes in ocean and atmospheric circulation, including at times marine anoxia
and acidification, and intensification of the hydrological cycle that included both
increased rainfall in some areas and increased drought in others (e.g., Wilson and
Norris, et al., 2001; Pagani et al., 2006). Consequences for marine and terrestrial
ecosystems were dramatic. Intervals of abrupt climate change documented by the
deep-time geological record—most notably, past hyperthermals—reveal how changes
in greenhouse gas concentrations can abruptly and profoundly influence climate and
life (Schaller et al., 2011; McElwain et al., 2005).
Deep-time geological records and the genomes of living organisms are also
rich archives of Earth's deep-time history. Mineral and biological environmental
indicators (proxies) record the interaction, feedbacks, and responses of physical,
chemical, and biological processes under the full range that the Earth system has
experienced (see Figure 2.18). A major challenge is to develop reliable proxy records
of atmospheric gases, surface temperatures, precipitation, relative humidity, and
marine and terrestrial productivity at a variety of temporal scales from millions to
thousands of years to address the multiple scales at which the processes act.
Opportunities for research exist in the development and calibration of new and
existing proxies, the construction of precise and accurate long- and short-term proxy
records at the requisite spatial and temporal resolution dictated by the hypotheses
being tested, including next-generation paleoclimate-data and model-model
comparisons.