The full programme book (PDF) - Royal Geographical Society

THEME 1: CAUSES OF CLIMATE CHANGE
Towards a unified theory of Quaternary climate variability:
the Heroic Age and the modern synthesis
Chronis Tzedakis
Department of Geography, University College London, London
The Heroic Age of Palaeoclimate Research saw the accumulation of an extensive body of
evidence on the nature of Middle and Late Pleistocene changes in the Earth System and
verification of the central tenet of the Milankovitch theory that astronomically-driven
variations in insolation cause changes in global climate. An important further development
was the realization of the extreme and pervasive nature of millennial-scale climate
variability, especially during intervals of increased ice volume.
Although important questions still remain (e.g. the origin of the 100-kyr cycles), significant
new strides towards a unified theory of glacial-interglacial cycles have been achieved in
recent years. Thus classical astronomical theory has been supplemented by a growing
recognition of the role of CO 2 in glacial-interglacial changes and the abrupt rather than
slow nature of climate transitions especially at glacial terminations, implying that the
interaction of orbital and millennial-scale may be an additional driver promoting
deglaciation. More specifically, while astronomical forcing dictates the broad timing of
interglacials, the actual mechanisms controlling glacial terminations may be related to the
critical size of ice sheets and bipolar-seesaw variability and its influence on CO 2
concentrations combined with ice-albedo and dust feedbacks. For glacial inceptions,
astronomical forcing reducing the amount of summer insolation is considered the primary
trigger, with CO 2 playing a secondary role along with a number of feedbacks and
mechanisms. However, the overall duration of an interglacial appears to be related to the
phasing of astronomical parameters and history of insolation, rather than its instantaneous
forcing value at inception.
This emerging synthesis is very much dominated by a ‘100-kyr world’ perspective, but the
strong non-linearity of the climate-cryosphere system during this period means that it is
unrepresentative of most of the glaciated part of the Cainozoic, where 41-kyr cycles
prevail. The Early Pleistocene of smaller ice sheets and reduced non-linearity provides a
more appropriate testbed for understanding the response of the climate system to orbital
forcing, but we still remain in relative ignorance over the character of orbital- and
millennial-scale variability and their interaction during this period. Any theory of ice ages
remains incomplete if it does not include an adequate description and understanding of
the ‘41-kyr world’ and the transition into the ‘100-kyr world’.
Key words: climate variability; orbital; millennial; heroic age; modern synthesis