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