More about the Programme
The latest research on recent climate variability (e.g. Mann et al. 1998) is tending increasingly to the view that greenhouse gas forcing is becoming the dominant, though not the only process driving the warming trend over the last 60 years or so. At the same time, detailed analyses of ice core records from glacial terminations show how closely atmospheric greenhouse gas concentrations track rapid warming (Petit et al. 1999), probably by acting as a major feedback mechanism during the transition to interglacial conditions. These and other lines of evidence from studies of the present- day atmosphere reinforce the view that future climate change will be driven by complex interactions between the effects of anthropogencially produced greenhouse gases and the effects of natural variability. There is therefore an urgent need to improve our documentation and understanding of natural variability for periods stretching back beyond the instrumental record (e.g. Briffa et al. 1995), much of which relates to the very period when anthropogenic effects appear to have been increasingly prominent.
Much natural variability, whether associated with mechanisms external or internal to the earth system, is expressed on inter-annual, decadal, and century time-scales. Variability on these time-scales and its interactions with future anthropogenic forcing are of outstanding relevance to human society. The need for a strong focus on high resolution records of climate variability on these timescales is highlighted by the growing extent to which climate and earth system modellers are beginning to run experiments that seek to replicate variability on these time-scales (e.g. Tett et al. 1999).
The urgent need to identify and understand the nature of inter-annual to century scale climate variability, reflects the need not only to inform and to evaluate the developing generation of models, but also to develop a more realistic temporal perspective for concepts like sustainability. Knowledge of past climate variability on these time-scales needs to be gained both from long-term instrumental records and from well-calibrated proxy data derived from natural archives.
In ideal circumstances such archives provide accurate records of climate history, can be dated with annual precision on a calendar year time-scale, can be inter-correlated through time and extend back through time to include the full range of variability of relevance to future prediction. In reality no single archive possesses such properties and climate reconstruction consequently needs to combine information from different sources, within and between geographical regions.
Resolving these methodological issues will allow us to tackle some of the more important questions relating to climate variability on these time scales that have been identified in the IGBP PAGES Europe-Africa study, PEPIII (see 8.1 below). In HOLIVAR, the focus will be on European climate variability, although North African issues will also be included as part of the Mediterranean Basin. The key questions are:
- to what extent can the instrumental record be used to identify patterns of climate variability e.g. associated with the NAO, over the last two centuries?
- to what extent can the longer term history of these modes of climate variability be reconstructed from proxy records? How have the periodicity, amplitude and effects of these oscillations varied in time and space?
- how are the characteristics of the widely accepted Little Ice Age and Medieval Warm Period expressed over the whole of the European and Mediterranean region, to what extent are spatially coherent trends identifiable? Over the longer timespan of the last 6,000 years how spatially coherent are cold and warm periods within high latitude regions, and how, and to what extent, are such periods expressed climatically in lower latitudes?
- what evidence is there for lower frequency multi-decadal and multi-centennial variations in climate within the European/Mediterranean region over the last 6,000 years. What is their periodicity, amplitude and cause?
- what is the nature and causes of periods of abrupt climate change that are evident from many low latitude records, especially in North Africa, and how and to what extent are these identifiable in other regions, especially within the Mediterranean basin?
- what evidence is there from proxy records to suggest that late twentieth century climates are unprecedented in the Holocene?
- how has climate variability over recent millennia affected biota and natural ecosystems along the transect?
- how has climate variability affected human activity and society over these time-scales?
Activities
- HOLIVAR 2006 - Final Open Science Meeting - 12-15 June 2006, London, United Kingdom Go to Website
- Workshops and Training Courses
- Email mailing list
A brochure containing more detailed information on HOLIVAR is available and can be downloaded by clicking here (PDF 159 KB)
