The IPCC process of Working Group 1 and
scientific improvements of Paleoscience
from AR1 to AR5
Jürg Luterbacher,
IPCC Lead Author, Ch5, Paleo
University of Giessen,
juerg.luterbacher@geogr.uni-giessen.de
http://www.climatechange2013.org/
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Outline of the talk
• What is the Intergovernmental Panel on Climate Change 
(IPCC)?
‐ The principals governing the IPCC process
‐ The structure and the 3 different working groups (WG)
‐ The process of WG 1
‐ Tasks of Authors
‐ Characteristics, facts and elements of the WGI 
contribution to IPCC AR5
‐ Impressions from the Summary for Policy negotiations in 
Stockholm September 2013
• The questions of Governments to Science
‐ Role of the Governments in the IPCC process
‐ Use of the answers from science in policy processes
• Paleoscience from IPCC FAR to AR 5; progress at continental 
to hemispheric scales since 1990
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• The Intergovernmental Panel on Climate Change (IPCC) is the 
international body for assessing  the science related to climate 
change.
• The IPCC was set up in 1988 by the WMO and UNEP to provide 
policymakers with regular assessments of the scientific basis of 
climate change, its impacts and future risks, and  options for 
adaptation and mitigation.
• IPCC assessments provide a scientific basis for governments at 
all levels to develop climate‐related policies, and they underlie 
negotiations at the UN Climate  conference – the United 
Nations Framework Convention on Climate Change.
• The assessments are policy‐relevant but not policy‐
prescriptive: they may present projections of future climate 
change based on different scenarios and the risks that climate 
change poses and discuss the implications of response options, 
but they do not tell policymakers what actions to take
What is the IPCC?
http://www.climatechange2013.org/
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Principles Governing IPCC work
http://www.climatechange2013.org/
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The structure of the IPCC?
http://www.climatechange2013.org/
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The 3 IPCC Working Groups (WGs)
http://www.climatechange2013.org/
• WG I assesses the physical science basis of the climate 
system and natural and anthropogenic climate change
(Release 27 September 2013, Final Report 30 September)
• WG II assesses the vulnerability of socio‐economic and 
natural systems to climate change, negative and positive 
impacts of climate change, and options for adapting to it 
(Release 31 March 2014)
• WG III assesses options for mitigating climate change 
through limiting or preventing greenhouse gas emissions 
and enhancing activities that remove them from the 
atmosphere
(Release 12 April 2014)
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The 5 IPCC reports so far (1990-2013)
http://www.climatechange2013.org/
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IPCC process (WG1)
http://www.climatechange2013.org/
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Tasks of IPCC Authors
http://www.climatechange2013.org/
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Characteristics of the IPCC Report
http://www.climatechange2013.org/
• Authors nominated by governments, observer 
organisations
• Selection of chapter teams based on expertise
• Attention to regional and gender balance
• Drafts are developed with multiple rounds of review
• Line‐by‐line approval of Summary for Policymakers by 
governments
• Presence of authors at approval ensures scientific 
accuracy
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Facts about the WGI contribution to
IPCC AR5
http://www.climatechange2013.org/
• 209 Lead Authors and 50 Review Editors from 39 
countries
• Over 600 Contributing Authors
• More than 2 million gigabytes of numerical data from 
climate models
• Over 9200 scientific publications cited
• 1089 expert reviewers from 55 countries and 38 
governments
• 54,677 review comments
• Was approved by almost 200 countries in September 2013
12http://www.climatechange2013.org/
The Elements of the 5th Assessment
Report, WG 1
14 Chapters
1'140'000 words, ca. 2000 pages
1250 Figures and Tables
Atlas: Regional Projections
Maps from 17 Regions of the World,
Digital form, 2 Mio G Bytes
Technical Summary
55'000 words, ca. 90 pages
Summary for Policy Makers
14'000 words, 22 pages, 10 figures
Synthesis Report
all WGs contribute (target 30 pages)
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Arrival of delegates and researchers in
Stockholm, September 2013, Monday
T. Osborn, pers. com.
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Wednesday evening, 20% of the words
were approved but 70% of the time had
elapsed, sessions extended to 2.30am
T. Osborn, pers. com.
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Delegates thinning out, authors still doing
email at 2.30am (except those
with their heads in their hands)...
T. Osborn, pers. com.
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Moving towards approval of final paragraphs
at 5am Friday morning, then some applause
breaks out as it becomes evident that
everything is approved ...
T. Osborn, pers. com.
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Friday, 27 September 10 am, about to
release the SPM...
T. Osborn, pers. com.
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Friday, 27 September 10 am, release of the
SPM, first page
http://www.climatechange2013.org/
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The questions of Governments to
Science (example Switzerland)
• What is known about the influence of anthropogenic 
greenhouse gas emissions (GHG) on the global climate 
system? 
• What are / may be the long‐term changes of the climate 
system?
• What are / may be the impacts of climate change on 
ecosystems, economic activities, human health, etc.? 
• What are the options for adapting to these changes? 
• What can be done to mitigate climate change? 
• Which methodologies do allow to estimate anthropogenic 
GHG emissions? 
J. Romero, Federal Dept. of Environ. 
Switzerland
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Getting the answers from science:
(example Switzerland)
J. Romero, Federal Dept. of Environ. 
Switzerland
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Role of the Governments in the IPCC
process
J. Romero, Federal Dept. of Environ. 
Switzerland
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Getting the answers from science:
(example Switzerland)
J. Romero, Federal Dept. of Environ. 
Switzerland
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Getting the answers from science:
(example Switzerland)
J. Romero, Federal Dept. of Environ. 
Switzerland
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Getting the answers from science:
(example Switzerland)
J. Romero, Federal Dept. of Environ. 
Switzerland
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Use of the answers from science in
policy processes (1)
Practically, how do the IPCC works help
policymakers (national and international level)?
J. Romero, Federal Dept. of Environ. 
Switzerland
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Use of the answers from science in
policy processes (2)
J. Romero, Federal Dept. of Environ. 
Switzerland
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Further Information
http://www.climatechange2013.org/
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AR 5, WG1, Chapter 5: Information
from Paleoclimate Archives, Authors
http://www.climatechange2013.org/
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AR 5, WG1, Chapter 5: Information
from Paleoclimate Archives, Content
http://www.climatechange2013.org/
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Paleoscience from IPCC FAR
to AR 5; progress at
continental to hemispheric
scales since 1990
First IPCC 1990: Schematic diagram of
‘global’ temperature variations for the
last thousand years (Fig. 7.1c)
Jones et al. 2009
--- IPCC 1990 Folland et al. 1990
--- Lamb 1982, annual, scaled with the black curve
--- CET (Manley et al. 1974, updated)
- no explicit calibration against instrumental data
- based on Lambs work in the 1960s and 1970s
- not a ‚global‘ curve, representative for Central England
SAR IPCC 1995: Northern Hemisphere
summer temperature variations back to 1400
- based on Bradley and Jones 1993 (Holocene)
- based on 16 proxy records (tree rings, ice cores, documentary records
- data sources: North America, Europe and East Asia
- calibration with instrumental data
TAR IPCC 2001: Northern Hemisphere
temperature variations back to 1000
- different reconstructions were presented in the Scientific Basis,
only Mann et al. (1998, 1999) was used for Summary for Policy
makers (the only reconstruction with uncertainties)
- multiproxy reconstruction
- truncated Principal Component analysis & inverse multiple regression
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Summary for Policy Makers TAR for
the last millennium NH
New analyses of proxy data for the Northern 
Hemisphere indicate that the increase in 
temperature in the 20th century is likely to have 
been the largest of any century during the past 
1,000 years.
It is also likely that, in the Northern Hemisphere, the 
1990s was the warmest decade and 1998 the 
warmest year. Because less data are available, less 
is known about annual averages prior to 1,000 years 
before present and for conditions prevailing in most 
of the Southern Hemisphere prior to 1861. 
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AR4 IPCC 2007: Northern Hemisphere
temperature variations back to AD 700
IPCC AR4, Fig. 6.10b
 Networks deteriorate back in time
 Differences in data network
 Dendroclimatic data dominate most reconstructions
 Different statistical approaches - empirical/physical
 Differences in spatial representativeness and methods
 Different target season (seasonal versus annual)
 Different calibration periods
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Summary for Policy Makers AR 4 for
the last millennium NH
Average Northern Hemisphere temperatures during 
the second half of the 20th century were very likely 
higher than during any other 50‐year period in the 
last 500 years and likely the highest in at least the 
past 1,300 years
AR 5 IPCC 2013: Reconstructed Northern,
Southern Hemisphere and global annual
temperatures during the last 2000 years
IPCC AR5, chapter 5, 2013
AR 5 IPCC 2013: Comparisons of simulated
and reconstructed NH temperature changes
IPCC AR5, chapter 5, 2013
39
Executive Summary AR 5 for the
last millennium NH
For average annual Northern Hemisphere 
temperatures, the period 1983–2012 was very likely 
the warmest 30‐year period of the last 800 years 
(high confidence) and likely the warmest 30‐year 
period of the last 1400 years (medium confidence). 
This is supported by comparison of instrumental 
temperatures with multiple reconstructions from a 
variety of proxy data and statistical methods, and is 
consistent with AR4. …
PAGES Initiative, 2000 years high resolution
continental climate reconstructions
PAGES 2k — Continental-scale regions
42
Continental temperature reconstructions
and paleo model simulations
PAGES 2k Consortium 2013;
IPCC AR5, chapter 5, 2013
Executive summary AR 5
Paleo temperature last 2000 years
Continental‐scale surface temperature reconstructions show, with high 
confidence, multidecadal intervals during the Medieval Climate Anomaly (950 to 
1250) that were in some regions as warm as in the mid‐20th century and in 
others as warm as in the late 20th century.
With high confidence, these intervals were not as synchronous across seasons and 
regions as the warming since the mid‐20th century. Based on the comparison 
between reconstructions and simulations, there is high confidence that not only 
external orbital, solar and volcanic forcing, but also internal variability, 
contributed to the spatial pattern and timing of surface‐temperature changes 
between the Medieval Climate Anomaly and the Little Ice Age (1450 to 1850).
44
Severity, duration, and frequency of droughts
in the Monsoon Asia and North American
IPCC AR5, chapter 5, 2013
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Flood frequency from paleofloods, historical &
instrumental records in selected European rivers
IPCC AR5, chapter 5, 2013
Executive summary AR 5 last
Paleo Droughts and Floods
There is high confidence for droughts during the last millennium of greater 
magnitude and longer duration than those observed since the beginning of 
the 20th century in many regions. There is medium confidence that more 
megadroughts occurred in monsoon Asia and wetter conditions prevailed in 
arid Central Asia and the South American monsoon region during the Little Ice 
Age (1450 to 1850) compared to the Medieval Climate Anomaly (950 to 
1250).
With high confidence, floods larger than those recorded since 1900 occurred 
during the past five centuries in northern and central Europe, western 
Mediterranean region, and eastern Asia. There is medium confidence that 
modern large floods are comparable to or surpass historical floods in 
magnitude and/or frequency in the Near East, India, and central North 
America.
Thank you very much for
your attention!