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Climate Change
Detection / Attribution
Organizer: Martin Visbeck, Columbia University
Co-organizer/Chair: Michael E. Mann, University of Virginia
SPEAKERS:
Gabi Hegerl, Duke University
Drew Shindell, NASA-Goddard Institute for Space Studies
National Academy of Sciences
Thirteenth Annual Symposium on
Frontiers of Science
November 8-10, 2001
Climate Change
Detection / Attribution
Introduction (Mann)
Q&A
Use of Models in Detection/Attribution (Hegerl)
Q&A
Causes of N.Hemisphere winter warming (Shindell)
Q&A
Discussion
National Academy of Sciences
Thirteenth Annual Symposium on
Frontiers of Science
November 8-10, 2001
25 min
5 min
25 min
5 min
25 min
5 min
30 min
Introduction to the Problem of
Climate Change Detection and
Attribution
Michael E. Mann
Department of Environmental Sciences
University of Virginia
National Academy of Sciences
Thirteenth Annual Symposium on
Frontiers of Science
November 8-10, 2001
`There is new and stronger
evidence that most of the
warming observed over
the last 50 years is attributable to
human activity'
Intergovernmental Panel on Climate Change (United
Nations), Third Assessment Report, 2001
OVERVIEW
•The Empirical Record
•Model Predictions
•Comparison between the two
•Key Outstanding issues
THE EMPIRICAL RECORD
Surface Temperature Changes
Climatic Research Unit (‘CRU’),
University of East Anglia
Climate Change 2001: The Scientific
Basis, Houghton, J.T., et al. (eds.),
Cambridge Univ. Press, Cambridge,
2001
TREE RINGS
CORALS
ICE CORES
VARVED LAKE SEDIMENTS
HISTORICAL DOCUMENTS
INSTRUMENTAL
TEMPERATURE
RECORD
GLOBAL PROXY
CLIMATE
RECORDS
RECONSTRUCTED
GLOBAL
TEMPERATURE
PATTERNS
MODEL PREDICTIONS
CO2
Related?
Greenhouse
Gases and
Warming
GREENHOUSE EFFECT?
ENHANCED GREENHOUSE EFFECT?
SIMULATED ANNUAL MEAN TREND 1949-1997
Knutson, T.R., T.L. Delworth, K.W. Dixon, and R.J. Stouffer, Model assessment of
regional surface temperature trends (1949-1997), Journal of Geophysical Research,
104, 30981-30996, 1999.
Modeled Natural Variability
Observations
COMPARISON BETWEEN MODEL
AND OBSERVATIONS
OBSERVED ANNUAL MEAN TREND 1949-1997
Knutson, T.R., T.L. Delworth, K.W. Dixon, and R.J. Stouffer, Model assessment of
regional surface temperature trends (1949-1997), Journal of Geophysical Research,
104, 30981-30996, 1999.
SIMULATED ANNUAL MEAN TREND 1949-1997
Knutson, T.R., T.L. Delworth, K.W. Dixon, and R.J. Stouffer, Model assessment of
regional surface temperature trends (1949-1997), Journal of Geophysical Research,
104, 30981-30996, 1999.
Inconsistent
with Natural
Variability
Inconsistent with
Greenhouse+
Sulphate Forcing
Vertical Fingerprint
Greenhouse
vs. Solar
Vertical
Fingerprint
ECHAM3/LSG MODEL
Climate Change 2001: The
Scientific Basis, Houghton,
J.T., et al. (eds.), Cambridge
Univ. Press, Cambridge, 2001
CLIMATE FORCINGS
Anthropogenic
Greenhouse
Gases
Industrial
Aerosols
CLIMATE FORCINGS
Volcanism
1000
1200
1400
1600
1800
Solar
Natural
2000
Simulated Annual Global Mean
Surface Temperatures
Climate Change
2001: The
Scientific Basis,
Houghton, J.T., et
al. (eds.),
Cambridge Univ.
Press, Cambridge,
2001
Forced Model
simulations
Energy Balance Model
(“EBM”) simulation
Science
Future Surface Temperatures Trends
Climate Change
2001: The
Scientific Basis,
Houghton, J.T., et
al. (eds.),
Cambridge Univ.
Press, Cambridge,
2001
KEY OUTSTANDING ISSUES
EL NINO/SOUTHERN OSCILLATION (“ENSO”)
Substantial interannual climate variability associated with
ENSO, but decadal variability is also evident as well. The recent
decadal trend towards El Nino conditions could be natural or
anthropogenic.
Multivariate
ENSO Index
(“MEI”)
NORTH ATLANTIC
OSCILLATION
Negative Phase
Positive Phase
NORTH ATLANTIC OSCILLATION
Trend in NAO in past couple
decades explains enhanced
recent warming in certain
regions of Northern Hemisphere
The
“Little Ice
Age”
Shindell et al
(Science, in press)
Empirical
LIA winter cooling in
Europe associated with
an NAO trend due to
solar irradiance
changes, interacting w/
stratospheric
atmospheric dynamics
and chemistry
NASA/GISS Model
NORTH ATLANTIC OSCILLATION
This NAO trend could
be Anthropogenic
CONCLUSIONS
•Recent global surface temperatures are
unprecedented this century, and likely at least the
past millennium
•It is difficult to explain the recent surface warming
in terms of natural climate variability
•Recent surface warming is largely consistent with
simulations of the effects of anthropogenic
influence on climate
•Unresolved issues regarding the precise
sensitivity of the climate to forcing, and changes in
ENSO, NAO, and regional responses