11.06.2014 Views

The full programme book (PDF) - Royal Geographical Society

The full programme book (PDF) - Royal Geographical Society

The full programme book (PDF) - Royal Geographical Society

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

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

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!