File:Deglaciation.png

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Description

The pattern of changes in Earth's orbit, known as Milankovitch cycles, that are believed to be responsible for triggering the onset of deglaciation.
Longer view of changes in temperature during the ice ages.

This figure shows a stack of the temperature and carbon dioxide profiles recorded in ice cores during the last 5 glacial terminations (i.e. the transition from the cold glacial phase of an ice age to a warm interglacial).

In each case, the transition takes ~8 thousand years and the onset of warming is believed to slightly precede changes in carbon dioxide. Caillon et al. (2003) estimated that temperature rise precedes carbon dioxide increases by 800 ± 200 years. This is consistent with the prevailing view that orbital changes (known as Milankovitch variations) provide the initial warming that starts the deglaciation (Hays et al. 1976). The increase in carbon dioxide that follows is not well understood, but leading speculation suggests that warming causes carbon dioxide to be released from the ocean (Petit et al. 1999). Through its action as a greenhouse gas the carbon dioxide (as well as methane and nitrous oxide) is believed to provide a feedback that amplifies the initial warming and ultimately leads to the full deglaciation. According to Caillon et al. (2003), the deglaciation in the Northern Hemisphere does not begin until after the greenhouse gases have begun to increase.

In total, greenhouse gases are believe to have contributed 30-40% of the warming associated with the end of the glacial period (Hewitt and Mitchell 1997). Much of the remainder is attributed to changes in albedo with open and newly vegetated lands absorbing more solar radiation than previously snow and ice covered lands.

Copyright

This image was created by Robert A. Rohde for Global Warming Art.


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This image is an original work created for Global Warming Art by Robert A. Rohde.

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Technical notes

Data used in this construction come from Vostok (deglaciations 1-4, Petit et al. 1999) and Dome C (deglaciation 5, EPICA 2004). For Vostok, direct temperature data was used. At Dome C, deuterium isotopic data as a proxy for temperature was scaled to Vostok; hence all temperature change are representative of the changes that occurred at Vostok, Antarctica. Such temperature changes are expected to be larger than changes in the global average. Glacial terminations 6 and 7, though available from Dome C, were excluded as being too qualitatively different to give a consistent presentation.

The individual records in the stack shown here were automatically lined to maximize the overlap. The smooth curves were produced by a Gaussian weighted moving average with effective width 1.5 kyr, with each deglaciation weighted equally (curves with more points were given less weight per point to compensate).

The resulting offset between temperature and carbon dioxide was ~400 years. However, the uncertainty associated with determining gas age from ice age can exceed 1000 years at these low accumulation sites (Caillon et al. 2003), and so the separation shown in the figure has been intentionally adjusted to match the 800 years found by Caillon et al.

A single outlying carbon dioxide measurement was not used during the fit and curve generation. This is marked with an open circle.

References

  • [abstract] [DOI] Nicolas Caillon, Jeffrey P. Severinghaus, Jean Jouzel, Jean-Marc Barnola, Jiancheng Kang, Volodya Y. Lipenkov (2003). "Timing of Atmospheric CO2 and Antarctic Temperature Changes Across Termination III". Science 299: 1728-1731. 
  • [abstract] [full text] [DOI] EPICA community members (2004). "Eight glacial cycles from an Antarctic ice core". Nature 429 (6992): 623-628. 
  • [abstract] [DOI] Petit J.R., Jouzel J., Raynaud D., Barkov N.I., Barnola J.M., Basile I., Bender M., Chappellaz J., Davis J., Delaygue G., Delmotte M., Kotlyakov V.M., Legrand M., Lipenkov V., Lorius C., Pépin L., Ritz C., Saltzman E., Stievenard M. (1999). "Climate and Atmospheric History of the Past 420,000 years from the Vostok Ice Core, Antarctica". Nature 399: 429-436. 
  • [DOI] Hays, J. D., John Imbrie, and N. J. Shackleton (1976). "Variations in the Earth's Orbit: Pacemaker of the Ice Ages". Science 194 (4270): 1121 - 1132. 
  • [abstract] Hewitt, C. D. and J. F. B. Mitchell (1997). "Radiative forcing and response of a GCM to ice age boundary conditions: cloud feedback and climate sensitivity". Climate Dynamics 13: 821-834. 

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Date/TimeThumbnailDimensionsUserComment
current01:44, 16 July 2007Thumbnail for version as of 01:44, 16 July 20071,000×664 (67 KB)Robert A. Rohde (Talk | contribs)
21:05, 15 July 2007Thumbnail for version as of 21:05, 15 July 20071,000×664 (67 KB)Robert A. Rohde (Talk | contribs)

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