RMC KTH Stockholm Abstract Z1 by 9reMKFB


									                         Deep Time to Our Time:

               The Scale Factor in Climate Change

                           A paper (with illustrations) presented at:

                Global Warming – Scientific Controversies in Climate Variability

                              KTH, Stockholm, Sept. 11-12, 2006

                                       R.M. Carter
                               Marine Geophysical Laboratory
                         James Cook University, Townsville, Qld. 4811

                                Email: bob.carter@jcu.edu.au

Climate change is a geological as much as a meteorological phenomenon. Yet
contemporary public discussion of the issue - influenced by the short-termist
approach of the Intergovernmental Panel on Climate Change (IPCC) - is concerned,
first, with the minutiae of temperature change over the last two decades of the 20th
century; and second, with the claimed abnormality of late 20th century warmth as
compared with the preceding, trivially short, 2000-year long, Christian era.

At best, our instrumental record of climate extends back for about 140 years, and
that only for a small number of locations worldwide. It is only since the deployment
of satellite sensors in the late 1970s that a high quality, genuinely global
meteorological dataset has become available. The ensuing 25 year-long data series is
shorter than even one “climate normal” interval, and therefore of inadequate length
to say anything very useful about climate change.

Geological records of climate change offer the great advantage of covering adequate
time spans to reflect natural climate change on all scales. However, they have their
own inadequacy in being inescapably based upon the measurement of proxy
indicators. For example, past temperatures are estimated from oxygen isotope data
from polar ice cores or oceanic mud cores.

Consideration of the last 16.000 year part of the well-dated, totemic Greenland ice-
core record exemplifies the ambiguity of using naive linear curve-fitting to answer
the apparently simple question “is warming occurring”, for the answer is controlled
entirely by the choice of start and end points (Davis & Bohling, 2001). In Greenland,
at least, warming has taken place since 16,000 years ago, and also since 100 years
ago. Over intermediate time periods, however, cooling has occurred since 10,000 and
2.000 years ago, and temperature stasis characterizes both the last 700 years and
(globally, from meteorological records) the last 7 years. Both the 7 and 100 year -
long intervals are too short to carry statistical significance regarding long-term
climate change. Therefore, the most useful comment that can be made about such
short-term data is that neither the rate nor the magnitude of temperature change in
Greenland during the late 20th century exceeds the natural levels recorded in earlier
instrumental and geological records.

The IPCC concentrates heavily on a radiative model of climate change. This approach
has been criticized by Kininmonth (2004) because it under-estimates the influence
on climate of the major meriodional heat flows transported within the world’s
atmosphere and ocean. The importance of oceanic heat flows is reinforced by Lyman
et al. (2006), who report that the global surface ocean heat anomaly has decreased
over the last two years, a finding which should lead us to reflect on the imbalance
between the time constants for heat turnover in the atmosphere (1 year) and ocean
(1000 years). A better understanding of climate change must involve a more
accurate treatment of the coupling of oceanographic and atmospheric heat flows,
and, in this regard, climate records from the mid-latitudes are of great importance.
Ocean drilling in the New Zealand region, Southwest Pacific Ocean, has yielded
important information about climate change, including the magnitudes and rates of
meridional heat transfer between south polar and tropical regions.

DSDP Sites 277 (520 S; 1210 m water depth) and 279 provided the first extended
Southern Ocean oxygen isotope record reflecting ocean temperature since about 60
Ma (Shackleton & Kennett, 1975). Subtropical warmth in the Eocene declined
gradually towards the 33.5 Ma Eocene-Oligocene boundary, where a sharp step-
cooling of several degrees corresponds to Antarctic glaciers first arriving at the coast,
with the subsequent formation of cold deep water. Temperature then fluctuated
spasmodically through the Oligocene and Miocene, to reach a warm peak again at
about 15 Ma, after which the temperature declined into the worldwide Pliocene-
Pleistocene glaciations.

The resolution of this record is only about 1 My, but that is adequate to suggest that
the major climatic fluctuations seen were forced by regional tectonic and global
oceanographic and atmospheric controls.

ODP Site 1123, located at latitude 420 S and 3290 m water depth, lies beneath the
Pacific Deep Western Boundary Current (DWBC). The ~20 Sv flow of the DWBC
represents about 40% of the input into the global ocean of cold, deep water, and is
thus a major agent of heat transfer. The oxygen isotope record from this site is typical
for the world ocean, and implies water temperatures that were significantly warmer
than today’s during past interglacials MIS 5, 9 and 11 (Hall et al., 2001). Parallel
grainsize studies reveal that fluctuations of intensity of the DWBC are closely coupled
with the climate signal, with stronger current speeds during glacial intervals. Even
small fluctuations in the strength of DBWC, or overlying AAIW, flow will of course
cause significant variations in the world surface ocean heat anomaly (cf. Lyman et al.,

ODP Site 1119, located at latitude 440 S, 395 m water depth, and beneath
Subantarctic Mode Water (SAMW), contains a 4 My-long record of shallow
intermediate water flow. Grainsize fluctuations at this site suggest that stronger
intermediate water flows occur primarily during warm interglacial periods (Carter et
al., 2004a). Natural gamma ray (NGR) measurements from the site reflect the
delivery of K-rich mud from the nearby New Zealand Southern Alps, and yield a
detailed local ice-volume record. This (inferred atmospheric) signal corresponds
closely at millenial scale with the Antarctic plateau temperature record reconstructed
from the Vostok ice core, and demonstrates a close integration of the changing
climate system across at least 450 of latitude (Carter et al., 2004b).

DSDP Site 594 lies a little seawards of Site 1119 and, at a depth of 1204 m, under
AAIW. The site has yielded a classic climatic record back to about MIS 19 and
beyond, and contains similar climatic lithological layering as that at 1119 (Nelson et
al., 1985; 1993). High resolution (1 mm spacing) colour reflectance measurements
provide a detailed record of changing carbonate content on a decadal time-scale
(Holland et al., 2005). Over the cold period between 20 and 30 ka, the 594
reflectance scans exhibit two 5,000 year climatic cycles that are modulated by
continually varying decadal climate fluctuations of similar wavelength and
magnitude to those seen in the 20th century global average temperature record.

Advancing our knowledge of climate change requires the collection of more and
better extended climate records from the marine realm. Alley (2003) has argued that
there is a strong need “to generate a few internationally coordinated, multiply
replicated, multiparameter, high time resolution type sections of oceanic (climate)
change”, using similar scientific protocols to those applied to polar ice coring.
Because of the energy flows that pass through them, the southern mid-latitudes are a
critical place where to locate one such type section. ODP Proposal 590-Pre
proposes to create the SnowMELT climate transect, a line of drillholes along
latitude 450 S that supplement the historic sites 594 and 1119 with new multi-cored
sites located in the South Island glacial lakes and on the west side of South Island.
Cores from the New Zealand region carry the unique advantages of high
sedimentation rates (i.e. high resolution climate signals), the availability of proxy
measures for both atmospheric and marine climate change, and the ability to study
the extended time periods required to elucidate the “deep time to our time” record of
natural climate change.


Alley, R.B. 2003 Raising paleoceanography. Paleoceanography 18, 9-1 to 9-2. DOI 10.1029/2003PA000942

Carter, R.M., Gammon, P.R. & Millwood, L. 2004a Glacial-interglacial (MIS 1-10) migrations of the Subtropical Front
(STF) across ODP Site 1119, Canterbury Bight, Southwest Pacific Ocean. Marine Geology 205, 29-58.

Carter, R.M. & Gammon, P. 2004b New Zealand maritime glaciation: millennial-scale southern climate change since 3.9
Ma. Science 304, 1659-1662.

Davis, J.C. & Bohling, G.C. 2001 The search for patterns in ice-core temperature curves. In: Gerhard, L.C. et al. (eds.),
Geological Perspectives of Global Climate Change, American Association of Petroleum Geologists, Studies in Geology 47,

Hall, I.R., McCave, I.N., Shackleton, N.J., Weedon, G.P. & Harris, S.E. 2001 Glacial intensification of deep Pacific inflow
and ventilation. Nature 412, 809-811.

Holland, M.E., Schultheiss, P.J., Carter, R.M., Roberts, J.A. & Francis, T.J.G. 2005 IODP's untapped wealth: multi-
parameter logging of legacy core. Scientific Drilling 1, 50-51.

Kininmonth, W. 2004 “Climate Change: a Natural Hazard”. Multi-Science Publishing, Brentwood, Essex, 207 pp.

Lyman, J.M., Willis, J.K. & Johnsopn, G.C. 2006 Recent cooling of the upper ocean. Geophys. Res. Lett., in press.

Nelson, C.S., Hendy, C.H., Jarrett, G.R. & Cuthbertson, A.M. 1985 Near-synchroneity of New Zealand alpine glaciations
and Northern Hemisphere continental glaciations during the past 750 kyr. Nature 318, 361-363.
Nelson, C.S., Cooke, P.J., Hendy, C.H. & Cuthbertson, A.M. 1993 Oceanographic and climate changes over the past
150,000 years at Deep Sea Drilling Project Site 594 off southeastern New Zealand, southwest Pacific Ocean.
Palaeoceanography 8, 435-458.

Shackleton, N.J. & Kennett, J.P. 1975 Paleotemperature history of the Cenozoic and the initiation of Antarctic glaciation:
oxygen and carbon isotope analyses in DSDP Sites 277, 279, and 281. Init. Repts. DSDP, vol. XXIX, Washington, U.S.
Govt. Printing Office, pp. 743-755.

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