Past Interglacials (PIGS)
Past Interglacials can be thought of as a series of natural experiments in which boundary conditions, such as the seasonal and latitudinal distribution of insolation, the extent of continental ice sheets and atmospheric greenhouse gas concentrations, varied considerably with consequent effects on the character of climate change.
Documenting interglacial climate variability, therefore, can provide a deeper understanding of the physical climate responses to underlying forcing and feedbacks. This provided the impetus to attempt a comprehensive comparison of interglacials of the last 800,000 years, within the context of a PAGES Working Group on Past Interglacials (PIGS), which ran from 2008 to 2015.
An initial PIGS workshop held at Bernin, France in October 2008, laid out the themes to be addressed at each of three subsequent workshops. A second workshop, held at the University of the Aegean, Island of Lesvos, Greece in August 2009, examined intra-interglacial variability and the onset of interglacials. The third workshop, held at Lamont-Doherty Earth Observatory of Columbia University, USA in October 2010, focused on the duration of interglacials and the ensuing glacial inception. The fourth workshop, held in Cambridge, UK in July 2012, focused on how well we can explain the diversity of interglacials from the forcing and feedbacks. A final writing workshop, took place in March 2013 at the Université catholique de Louvain, Louvain-La-Neuve, Belgium.
In a series of papers, synthesizing the state of knowledge, PIGS identified the following key concepts:
- Examination of the palaeoclimate record of the last 800,000 years reveals a large diversity among interglacials in terms of their intensity, duration and internal variability (Reference 1).
- The fundamental concept of an interglacial is that of the sea-level highstand, a measure of integrated global climate effects, which lead to the loss of continental ice (2).
- Interglacials may therefore be defined as intervals of little or no northern hemisphere ice outside Greenland. On this basis, eleven interglacials (MIS 1, 5e, 7a-c, 7e, 9e, 11c, 13a, 15a, 15e, 17, 19c) were identified over the last 800,000 years, a result that is robust to alternative definitions (3).
- MIS 5e and 11c were globally warm, while MIS 13a was cool at many locations. A step change in strength of interglacials at 450,000 yr BP is apparent only in atmospheric CO2, and in Antarctic and deep ocean temperature (1,3).
- The onset of an interglacial (glacial termination) requires increasing northern hemisphere summer insolation, but this condition alone is insufficient. Terminations involve rapid, non-linear, reactions of ice volume, CO2 and temperature to external astronomical forcing (3).
- The end of an interglacial (glacial inception) is a slower process involving a global sequence of changes (3,4).
- A variety of temporal trends within interglacials is observed, such that maxima in the main records are observed either early or late in different interglacials (2,3).
- Interglacials have been typically 10,000-30,000 years long (2,3).
PIGS has now evolved into the PAGES Working Group on Quaternary Interglacials (QUIGS), which aims to document and synthesize palaeoclimate data and use targeted climate model exercises towards a systematic understanding of the causes of interglacial warmth.
For more information about QUIGS, go here.
(1) Tzedakis PC, Raynaud DR, McManus JF, Berger A, Brovkin V & Kiefer T (2009) Interglacial diversity. Nature Geoscience 2, 751-755, doi:10.1038/NGEO660.
(2) Tzedakis PC, Wolff EW, Skinner LC, Brovkin V, Hodell DA, McManus JF & Raynaud D (2012) Can we predict the duration of an interglacial? Climate of the Past 8, 1473-1485, doi:10.5194/cp-8-1473-2012.
(3) Past Interglacial Working Group of PAGES (2016) Interglacials of the last 800,000 years. Reviews of Geophysics, doi:10.1002/2015RG000482.
(4) Mokeddem Z, McManus JF & Oppo DW (2014) Oceanographic dynamics and the end of the last interglacial in the subpolar North Atlantic, Proceedings of the National Academy of Sciences 111, 11263-11268, doi:10.1073/pnas.1322103111.
Lateglacial and Holocene palaeoclimate records. (a) sea- level reconstruction (Lambeck and Chappell, 2001); (b) δ 18 O com- position of ice in the NGRIP ice core, Greenland (North Greenland Ice Core Project members, 2004); (c) δ D composition of ice in the EPICA Dome C (EDC) ice core (Jouzel et al., 2007). Grey band denotes the position of the Younger Dryas (YD) stadial. In: Tzedakis, P. C., Wolff, E. W., Skinner, L. C., Brovkin, V., Hodell, D. A., McManus, J. F., and Raynaud, D.: Can we predict the duration of an interglacial?, Clim. Past, 8, 1473-1485, doi:10.5194/cp-8-1473-2012, 2012. link
Past Interglacials Working Group of PAGES, 2016. "Interglacials of the last 800,000 years," Reviews of Geophysics, 2015RG000482. doi: 10.1002/2015RG000482.
In the context of future climate change, there is a need to understand the sensitivity of the Earth System to different scales of forcing during interglacials. As responses are not easily extrapolated from current observations, the geological record can provide an insight into the behavior of different components of the Earth System.
In this respect, previous interglacials can be thought of as a series of natural experiments in which boundary conditions varied, with consequent effects on the character of climate change. Examining a single glacial-interglacial cycle can only reveal part of the picture; studying additional cycles can give us a more complete view of the range of natural climate variability and biotic response.
The PAGES Working Group on Past Interglacials (PIGS) was launched in 2008 to co-ordinate research and promote international co-operation on various aspects of interglacials. PIGS held a series of workshops and prepared research and synthesis publications.
Now that PIGS has finished, become involved with the new QUIGS working group here.