The 1500 Year Quasiperiodicity During the Holocene - Abrupt Climate Change: Mechanisms, Patterns, and Impacts - page 168

functions characterizing the ocean and solar variabilities
(right plots).

1,500 years. That means humanity s response must be keyed

to adaptation, not prevention. ” The current warming trend,
according to these authors, began about 1850, and

'

The 1500
year cycle typically produces a temperature change of four to
five degrees centigrade from peak to trough. Temperature
changes are greater in the Arctic. At the equator, however,
the temperatures do not change

“

6. DISCUSSION

The progress in the collection of paleodata greatly stimu-
lates the reconstruction of the climate of the past and gives
insight into the climate of the future. With a focus on the
nature of the millennium variability during the Holocene, we
have shown that the 1500 year oscillation is not purely
random; thus, forcing is involved. We have suggested a
simple model of excitation of this oscillation in a nonlinear
dynamical system with two equilibrium states. The transi-
tions between the two states are caused by noise, ocean, and
solar variability. This implies that it is the beats between the
centennial ocean variability [Vellinga and Wu, 2004] and 90
year solar variability that produces the 1500 year oscillation
in the noisy system. Note that the frequencies of solar and
ocean variabilities are both known to be unstable. This
simple model needs to be validated by more sophisticated
coupled ocean-atmosphere models. The modeling should
start with a GCM simulating the centennial ocean variability
and then be forced by the 90 year solar variation.
An interesting question is whether or not the 1500 year
variability is limited to the Atlantic. Isono et al. [2009] using
a multidecadal resolution record of alkenone SST in the
northwestern Paci

the rainfall does. The trop-
ical rain belts at the equator can move hundreds of miles
north and south during the cycle.

—

”
Our data analysis does not support the basic assessment
of these authors since the amplitude of the 1500 year
oscillation is smaller than 1°C; see, for example, Figure 5
and paper by Isono et al. [2009]. So the rise of 1500 year
oscillation could not compete with the predicted tempera-
ture rise of 2°C 5°C per century due to the increase in

CO 2 and other greenhouse gases. However, the 1500 year
variability may be taken into account in historical and
possibly future considerations.

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Acknowledgements. We have obtained the GISP2, West Africa,
and Cariaco paleodata from the NOAA/NGDC Paleoclimatology
Program and acknowledge the scientists who provided these data
(see references in Section 2). We are very grateful to David Thor-
nalley, Masanobu Yamamoto, and Isla Casta ñ eda for providing their
paleodata and helpful communications. This work was supported in
part by the Jet Propulsion Laboratory of the California Institute of
Technology, under a contract with the National Aeronautics and
Space Administration.

c off central Japan have found the mil-
lennial variability with an amplitude of about 1°C throughout
the entire Holocene. Spectral analysis carried out by Isono et
al. revealed a statistically signi

REFERENCES

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