Future prospects - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 364

or, more generally, climate change in the NH vs. climate change in the SH. The main
problem in comparing climate data in the NH and the SH is achieving precise
absolute chronologies. Because layers can be counted at Greenland, the chronology
is much more precise and highly resolved, at least over the past 40,000 to 50,000
years. By contrast, the Antarctic chronology has less precision and resolution. In this
connection, the West Antarctica Ice Sheet Divide (WAIS Divide) project will bore a
deep ice core from the flow divide in central West Antarctica in order to provide
Antarctic records of environmental change with the highest possible time resolution
for the last 100,000 years and will be the Southern Hemisphere equivalent of the
Greenland GISP2, GRIP, and North GRIP ice cores. The most significant and
unique characteristic of the WAIS Divide project will be the development of climate
records with an absolute annual-layer-counted chronology for the most recent
40,000 years. It is hoped thereby to determine (a) the role played by greenhouse
gases in ice ages and (b) whether the initiation of climate changes occurs preferen-
tially in the south or the north. Drilling was completed in 2011 and analysis is under
way. Thus, it is of great importance that the WAIS project be pursued and com-
pleted as planned.
Stott et al. (2007) and Timmermann et al. (2009) found experimental and
theoretical evidence that ice age terminations may originate near Antarctica—and
not in the NH. This line of research may provide further advances in our
understanding of the roles of the north and south in glacial-interglacial cycles.
Role of oceans The role of the oceans in climate change and glacial-interglacial
cycles has been discussed by a number of authors, particularly regarding abrupt
climate change (see Section 8.6). However, much of this is based on modeling and
conjecture. We need to collect more data on the past variability of ocean currents
and temperatures. Extension of studies such as that of Piotrowski et al. (2004) to
determine past ocean circulation will be very helpful.
Clark et al. (2002) concluded: ''Although understanding the mechanisms
behind abrupt climate transitions in the past is interesting in its own right, there is
a pressing need to gain insight into the likelihood of their future occurrence.''
They suggested that ''progress towards a mechanistic understanding of abrupt
climate change can be expected from coupled models with higher resolution,

that no longer require flux adjustments, and that include biogeochemical cycles.''
Experiments such as the World Ocean Circulation Experiment can provide
important information on heat transport by the oceans (Ganachaud and Wunsch,
2002). Schmidt et al. (2004) analyzed two Caribbean Sea sediment cores to recon-
struct tropical Atlantic surface salinity during the last glacial cycle. They found
that Caribbean salinity oscillated between saltier conditions during cold periods
and lower salinities during warm periods, varying in consonance with the strength
of North Atlantic Deep Water formation. Thornalley et al. (2011) found evidence
that thermohaline circulation has played a role in climate change since the Last
Glacial Maximum.
Direct measurement of climate sensitivity One of the critically important
unknowns in climatology is the current sensitivity of the climate to increasing CO 2
concentration. Lindzen (1997) suggested several possible approaches for direct

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