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 3: MEASURING AND UNDERSTANDING CLIMATE CHANGE<br />
Measuring and understanding climate change<br />
Valérie Masson-Delmotte<br />
IPSL/LSCE (CEA-CNRS-UVSQ), Gif-sur-Yvette, France<br />
This presentation will be focused on a bipolar perspective on climate change, based on<br />
quantitative estimates of past temperature changes from Greenland and Antarctic ice<br />
cores.<br />
<strong>The</strong> state of the art regarding the quantification methods will be briefly reviewed. <strong>The</strong>y<br />
combine information from water stable isotopes (including the use of atmospheric models<br />
enabled with water stable isotopes), borehole temperature profile inversions, and<br />
gravitational and thermal gas fractionation.<br />
<strong>The</strong> main findings based on these records will then be summarized throughout different<br />
time scales. <strong>The</strong> overlap between internal variability, response to orbital, solar and<br />
volcanic forcing, and anthropogenic effects will be discussed within the framework of<br />
Greenland/Arctic and Antarctic temperature records spanning the last centuries/millennia.<br />
<strong>The</strong>y stress the gap in understanding the mechanisms driving Antarctic temperature<br />
variations.<br />
<strong>The</strong> understanding of multi-millennial temperature trends during the current and last<br />
interglacial periods will be discussed using temperature estimates from ice cores together<br />
with transient simulations conducted with different climate models. Again, this comparison<br />
highlights a model-data mismatch with respect to Antarctic temperature, stressing the lack<br />
of understanding of the mechanisms at play. While the NEEM ice core data have been<br />
used to constrain past changes in Greenland elevation and therefore, combined with ice<br />
sheet simulations, its contribution to sea level change during the last interglacial period,<br />
the contribution of the Antarctic ice sheet to sea level change during the last interglacial<br />
period remains an open issue.<br />
<strong>The</strong> bipolar approach is particularly useful for abrupt events during the last glacial period,<br />
which involve major reorganizations of the Atlantic Meridional Ocean Circulation. <strong>The</strong><br />
synchronisation of ice cores is critical with respect to the characterisation of the bipolar<br />
seesaw pattern. <strong>The</strong> matrix of ice cores allows to characterize the regional structures of<br />
temperature changes, which is expected to reflect the impact of changes in regional sea<br />
ice / atmospheric circulation patterns. Regional Greenland temperature gradients have<br />
recently been identified along Dansgaard-Oeschger events, showing a structure which is<br />
consistent with the simulated fingerprint of changes in Nordic Seas sea ice extent. Ice core<br />
records also reveal regional patterns in their Antarctic fingerprint (Antarctic Isotopic<br />
Maxima). A faster warming rate is estimated in the Atlantic sector, when compared to the<br />
Indo-Pacific ice core records, possibly associated with fast atmospheric teleconnections.<br />
Recent works have also identified a potential fingerprint of Heinrich events within<br />
Greenland stadials, challenging the classical simulation of stadials through freshwater<br />
hosing into climate models.<br />
Finally, the glacial-interglacial sequence of events is relevant for issues such as polar<br />
amplification, climate and carbon cycle feedbacks, and climate sensitivity. <strong>The</strong> focus will<br />
be placed here on recent findings regarding the timing and patterns of Antarctic<br />
temperature changes with respect to changes in atmospheric CO2 concentration during<br />
the last two terminations.<br />
Key words: ice cores; temperature; last millennium; glacial-interglacial variations; abrupt events