date: Wed Dec 18 14:03:03 1996
from: Keith Briffa <k.briffa@uea.ac.uk>
to: Paul Sinclair

Report of the PEP III Stream 1 Working Group
convened at the IGBP-PAGES Workshop,
Bierville, Sept. 12-15, 1996.


Introduction

This group was charged with reviewing the potential sources of qualitative, high-resolution 
evidence of climate variability and climate change on interannual, decadal and century 
timescales along the PEP III transect within the Stream 1 timeframe of the last 2000 years.  
The group discussed the specific strengths and limitations of various types of climate proxies 
and reviewed their temporal and spatial coverage.  A principal aim of the group was to re-
examine and, where possible, redefine major foci for PEP III Stream 1 activities in the 
medium term, taking account of ongoing initiatives, identifying new opportunities and 
highlighting possible geographical imbalances.  The following is a brief description of the 
outcome of the discussions around these topics, including a summary of the major 
conclusions and recommendations of the group.  An expanded review and discussion 
document, in the form of a revised implementation plan for PEP III Stream 1 activities, is 
currently being prepared.

Rationale and General Objectives
The group recognised that the particular importance of general Stream 1 activities, within all 
PEP transects, arises from the need to define accurately the history of climate variability on 
interannual and decadal, as well as longer, timescales.  Well-dated, high-resolution climate 
information from before the period of possible human modification and for sites where 
human modification over the last 2000 years has been minimal, is essential if we are to 
understand the mechanisms of natural climate change and rigorously ascribe causes.  It 
follows that there exists a concomitant need to establish quantitatively, and with equal 
accuracy, the histories of potential climate forcing agents - such as changes in solar output, 
volcanic activity, etc.  The reconstruction of both climate and climate-forcing histories 
within the Stream 1 timeframe is also highly relevant for attempts at rigorous attribution of 
recent climate change to anthropogenic causes.

In parallel with the general ambitions of all PEP transects, the group therefore defined the 
ultimate aims of PEP III Stream 1 activities as follows:
1.	To document the full range of climate variability that has taken place across the 
Western Eurasian and African continents over the last 2000 years.

2.	To identify factors responsible for causing climate change.

3.	To provide datasets for the parameterization and validation of climate models.

4.	To explore the influence of climate change on human activity and the influence of 
human activity on climate change.

To accomplish these objectives requires sensitive methods because the likely magnitude of 
change is considerably less in recent millennia than on longer, e.g. Milankovitch, timescales.  
It was also agreed that studies within Time Stream 1 should not be constrained by the 
2000-year limit if longer timescales within the Holocene could be embraced with equivalent 
precision and accuracy.


Important Systems and Proxies
The history, current state and prospects for future development of a number of major 
sources of paleoclimate and palaeoenvironmental sources were discussed.  The group 
focussed attention on their major strengths and known weaknesses and explored the 
immediate prospects for better exploiting these sources and extending the geographical 
range within the PEP III transect.  These sources and the specific proxies that they provide 
will be discussed in more detail in the forthcoming Stream 1 implementation plan.  They 
include
1.	Instrumental Records
2.	Historical and Documentary Records
3.	Tree Rings
4.	Ice Cores
5.	Speleothems
6.	Lake Sediments
7.	Marine/Large Lake/Inland Sea Sediments
8.	Peats
9.	Archaeological Records

A PEP III Perspective
Though the primary axis of interest in PEP III activities is defined north to south, the 
east/west dimension is significant in terms of the large distances across Europe and Africa 
and because of the existence of large climate gradients.

Localised records that provide well-calibrated climate information are valuable in their own 
right, the more so where they are of high-resolution (seasonal or annual) and where the 
dating is good.  Even more valuable are similar records or data sources that occur along one 
or more parts of the PEP III transect, or better still, that have extended spatial or network 
coverage across large regions.

While recognising these optimum data attributes, the group felt strongly that the 
development of data sources that meet only some of these criteria was still to be strongly 
encouraged.  All proxy data sources are limited in different ways in their ability to represent 
climate variations and a multi-proxy approach to palaeoclimate research is most likely to 
yield maximum results.  Different records will respond to different climate parameters.  
Comparison of different records will identify similarities and differences - providing either 
mutual support for, or raising questions and suggesting alternative interpretations of, the 
different data.  The multiproxy approach should highlight individual data limitations; in some 
cases allowing refinement of the dating control; provide better understanding of the time-
averaged or lag responses, and generally lead to a more accurate and complete picture of 
climate changes than can be achieved using individual data sets in isolation.

Regional Foci
To optimise resources, taking account of ongoing research projects and recognising the 
current geographical imbalance in traditional regions of high-resolution palaeoclimate 
research, the group recommended a number of areas where future research might be usefully 
concentrated.  Above all, these are regions of major importance within the global climate 
system.  Instrumental records and modelling studies indicate that climate variability in each 
of these areas is influenced by characteristic large-scale modes of variability of the general 
atmosphere or the interaction of the atmosphere with the oceans.

The regions identified were
1.	The mid-to-high-latitude section (~north of 60 N) of Fennoscandia and western and 
central Russia
2.	Western Europe and the Mediterranean regions under the influence of the North 
Atlantic Oscillation
3.	Monsoon Effected areas of West Africa
4.	Northeast Africa and the Nile Valley
5.	Southern Africa and Madagascar

An Archaeological Emphasis
Until now, there has been little mention in Stream 1 discussions of the potential for 
generating past climate information through the use of high-resolution historical and, 
particularly, archaeological data.  Archaeology and PEP III Stream 1 studies in general, will 
gain reciprocal benefits through a greater emphasis on selected archaeological studies and 
increased collaboration between archaeologists and palaeoclimate scientists.  Both require an 
understanding of how people have impacted on the natural environment, not least in order to 
interpret proxy climate data.  Initiating the development and study of these data in areas of 
high archaeological potential will be invaluable for understanding human responses to 
climate and other environmental change.  Though such studies are feasible throughout the 
PEP III transect, they should be especially encouraged in areas where there is known 
potential to generate high-resolution data in space (local and regional) and time (annual-
decadal) and that could be used to make comparisons with changes in human activities in 
other regions.

Areas of proven archaeological potential occur widely in all parts of Europe, the 
Mediterranean and many parts of Africa.  However, the group identified the following 
selected list.
1.	The Nile Valley
2.	East African Highlands and Coast
3.	Madagascar Highlands and Coast
4.	Southern Africa
The background and specific rationale for highlighting these regions will be outlined in detail 
in the forthcoming PEP III Stream 1 Implementation Plan.  These regions coincide with 
most of the regions already identified as important potential regional research foci.


Important Methodological Issues
	The group reviewed a number of issues of relevance to the interpretational value of 
palaeoclimate sources in general, and particularly in the context of Stream 1 objectives.  The 
group consensus was to encourage explicit recognition among research workers of the 
importance of these topics.  It was felt that experimentation with different palaeoclimate 
sources should attempt to address each of these issues explicitly and that direct reference to 
their particular significance be included in reports or research publications dealing with those 
sources.

1.	Resolution
	The desirability of high resolution palaeodata has been stressed already.  True annual 
resolution and, where it can be achieved, subannual resolution offer the prospect of specific 
seasonal reconstruction of climate and evidence of the annual cycle range.  Some records 
may, however, be annually or sub-annually resolved, but may only reflect climate forcing at a 
specific time of the year.  Conversely, annually registered data may still only reflect longer-
term climate forcing, integrated over a number of years.
	Where annual resolution cannot be achieved, efforts should be made to establish the 
true resolving power of the data and the extent to which the resolution varies in time.  While 
recognising the desirability of annual or subannual resolution, the group systems were 
decadal resolution can be attained e.g. many lake and mire systems, particularly where 
tephrochronology might provide additional precise links to other time series.

2.	Dating and Chronology
	The importance of strong dating control, particularly within the context of Stream 1 
studies, cannot be overemphasised.  The value of statistical techniques for testing the 
association between different climate reconstructions, or between deduced climate variability 
and evidence of forcing agents, is highly dependent on accurate chronology.  Even where 
palaeorecords are deposited annually or display annual layering, simple counting of the 
layers does not guarantee absolute dating accuracy.  Some individual year boundaries may 
be ambiguous.  In any individual record, depositional discontinuities or hiatuses or post-
depositional disruption can occur.  Where practical, comparisons of duplicate records at a 
site, or from adjacent sites, can confirm the dating accuracy or identify anomalies and enable 
the timescale to be corrected.  When annual dating control is not feasible for a particular 
record, comparison with features of other, better-dated records may improve the 
chronology.  Again, where feasible, multiple approaches to dating should be adopted.  
Where there is uncertainty in the dating, this must be clearly expressed.

The group laid great stress on the desirability of adapting multiple approaches to dating time 
series in situations where absolute chronology is not routinely attainable.  In this respect it 
was felt that the continued development of tephrachronologies and studies intended to 
explore the potential of using specific tephras as absolute dating horizons or time markers in 
many ice, lake, peat or other palaeodata sources should be noted.

3.	Replication
	Analysing multiple or replicate samples of some proxy data record, besides helping to 
establish good dating control in the timeseries, is highly desirable because it provides a basis 
for quantifying the underlying signal strength represented in that record.  Even perfectly 
dated, duplicate, records will not agree perfectly.  The degree of similarity, however, will 
give an indication of how strongly the underlying forcing is represented in each series.  The 
degree of difference is an indication of noise.  Averaging replicate series (provided they 
have good dating control) will reduce the noise and produce a record which better expresses 
the underlying forcing.  Because so much more information can be gleaned from duplicated 
records and higher, quantifiable confidence achieved by producing a mean series, duplicate 
sampling should be undertaken wherever possible.

4.	Calibration
	Climate inferences drawn from palaeodata should be supported by rigorous statistical 
comparisons with observed meteorological data.  Statistical regression equations or transfer 
functions applied to high-resolution palaeodata series to estimate past climate variability, 
should be calibrated in the time domain and not be based only on spatially-derived 
relationships.  Where possible, empirical or statistical approaches to inferring past climate 
variability should be supported by theoretical modelling studies.  Realistic confidence limits 
on palaeoclimate estimates should be provided.

5.	Signal Representativeness
	Researchers should strive to make explicit the potential weaknesses or limitations in 
the representativeness or accuracy of their past climate inferences based on their detailed 
knowledge of the palaeodata and systems with which they work.  For example, some 
records may represent high-frequency (interannual) climate forcing with good fidelity, but be 
limited in their ability to represent the same forcing on longer timescales, perhaps because 
the systems are able to adapt to gradual changes in forcing.  Longer-timescale variations 
may, of necessity, be removed in the production of a palaeorecord perhaps because the 
primary data are known to be influenced on these timescales by processes other than the 
climate forcing of interest.  Separate calibrations of a palaeorecord after spectral 
decomposition might highlight differences in the fidelity of the climate interpretation on 
different timescales.  However, the short length of many available climate records will limit 
the extent to which even decadal-to-century timescale fidelity can be demonstrated.

6.	Human Impact
	It is possible, even probable, that instrumentally recorded climate data are already 
registering anthropogenic disturbance of the natural climate system.  In addition, many 
other aspects of the natural environment have been modified by humans.  In some localised 
areas this may have occurred over thousands of years.  On much larger, even global scales, 
changes in atmospheric and terrestrial environments have certainly occurred over the last 
century.  These include increasing concentrations of greenhouse gasses, heavy metal 
pollution, and nitrogen and sulphur deposition.  Reductions in stratospheric ozone and 
increased surface ultraviolet radiation levels have been dramatic in recent decades. The 
potential for these and other factors associated with human activities to complicate the 
calibration of palaeodata against modern instrumental records must be appreciated.  The 
degree to which any or a combination of these might affect the long-term validity of modern 
palaeodata/climate associations will be difficult to establish.  The relative importance of 
different factors will obviously vary greatly according to the data source, and the specifics of 
the physical or biological systems involved.  Still, future work must aim to provide 
quantitative answers.  A combination of statistical, theoretical and experimental approaches 
will almost certainly be required.

Conclusions and Recommendations
	The following is a list of the major conclusions arising out of the Stream 1 group 
discussions and includes a brief outline of the recommendations agreed by those present.  
The list is not prioritised.

 	A major focus of PEPIII Stream 1 research should be on establishing the degree to 
which 20th century climates are unprecedented.  This must involve quantitative 
reconstruction of past mean climates on multidecadal and century timescales as 
well as interannual variability and the frequency of extremes.

 	There remains a widespread preconception that the Little Ice Age and Medieval 
Warm Epoch were ubiquitous features of the climate history of the last two 
millennia.  There is still a need to further clarify the definition of these concepts in 
terms of their character, extent and precise timing, even within Europe.  More 
research is required to establish the extent to which the concepts of the Little Ice 
Age and Medieval Warm Epoch are valid or relevant in other areas of the transect.  
Future research must attempt to clarify whether, if real, these phenomena 
represent unique events within the last 2000 years, and, if possible, in the earlier 
Holocene.

 	Traditionally, high-resolution studies within the Stream 1 timeframe have been 
very much concentrated in the mid-to-high latitudes of the northern part of the 
PEPIII transect.  In part, this is simply a result of proximity to established research 
situations.  However, it also reflects genuine difficulty in locating datable, high-
resolution records in low latitudes and in the African part of the transect.

	The existence of numerous, long tree-ring chronologies in Morocco is an 
important exception.  Some potential for other dendroclimatological studies in 
north and east Africa has been clearly demonstrated and the future development of 
this potential should be explored.

 	Given the problems of identifying annually resolved palaeosources in Africa, the 
group laid stress on the need to explore other less-well-resolved sources, 
particularly  where they might be represented across wide areas of the transect.  
The concept of a specific research initiative aimed at exploring climate proxies in 
the sediments of a series of African crater lakes along the East African section of 
the transect was considered worthy of prioritisation.

 	Even in Europe, there is important potential for identifying and processing 
historical and early meteorological records.  Some palaeoseries, produced perhaps 
decades ago, now require updating.

 	More research is required in order to identify and gauge the significance of 
anthropogenic environmental disturbance and the implications for palaeoclimate 
estimates calibrated against modern climate data.

 	Collaborative projects, which involve comparison and an integrated approach to 
the interpretation of different climate proxy sources in areas where these are 
available, are not common.  More projects should be initiated that bring together 
palaeoclimate scientists working with different systems (e.g. with ice core data, 
tree rings, lake sediments).

 	Archaeological data have been underutilised in a palaeoclimate context.  
Collaboration between archaeologists and palaeoclimatologists, especially in areas 
with a tradition of detailed high-resolution archaeological work and historical and 
palaeoclimate proxies, should be promoted.  Several regions, such as in the 
Mediterranean and in monsoon areas (particularly in Egypt) and in the south of 
Africa, are potential foci for such efforts.

 	More attention to formal calibration studies and a routine quantitative evaluation 
of palaeoclimate data and reconstruction confidence limits, are encouraged, as is 
the establishment of standard calibration training sets, such as could be used for 
the interpretation of widespread data, such as chironomids.

 	Intense attention to accurate chronology is encouraged in situations where 
absolute dating is not feasible.  This might involve multiple dating proxies.

 	Work to establish a detailed network of tephra histories in the circum North 
Atlantic Region and the possibility of developing a widely applicable tephra 
chronology to provide fixed dating points for many less-well-resolved data 
sources is noted.

 	The further development of the European palaeodata archive in Marseilles (linked 
to the World Data Center-A for Paleoclimatology in Boulder) is seen as 
fundamental to the feasibility of achieving the aims of PAGES PEPIII Stream 1.  
Universal submission of palaeodata and the free interchange of these data through 
the medium of the PEPIII data archive is crucial for the future success of Stream 1 
research.




