palaeo-constraints on future climate change mat collins, school of engineering, mathematics and...
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Palaeo-Constraints on Future Climate Change
Mat Collins, School of Engineering, Mathematics and Physical Sciences, University of Exeter
Tamsin Edwards (Bristol), Tom Russon (Edinburgh), James Pope (Leeds) + many others
#RMetSMeet
Current Status of Global Projections
Reto Knutti and Jan SedláčekNature Climate Change, 2012
Climate Models and Modellers
• A significant fraction of climate science is in modelling, understanding, prediction and projection of future climate change• “What can studying palaoclimates do for us?”
• Palaeoclimate reconstructions have been influential in showing that the climate could have been much different • And have motivated modellers to reconfigure their models and run simulations of palaeoclimate• But can they help improve models and reduce uncertainties in projections in a quantitative way?
Example: Last Glacial Maximum
QUMP/PalaeoQUMP Simulations
Example: Last Glacial Maximum
QUMP/PalaeoQUMP Simulations
Example: Last Glacial Maximum
QUMP/PalaeoQUMP Simulations
Example: Last Glacial Maximum
QUMP/PalaeoQUMP Simulations
CS=3.7K
Example: Last Glacial Maximum
QUMP/PalaeoQUMP Simulations
Example: Last Glacial Maximum
QUMP/PalaeoQUMP Simulations
Example: Last Glacial Maximum
5-95%: 2.3K-5.0K
QUMP/PalaeoQUMP Simulations
5-95% range 2.3-4.3K
Sexton et al. 2012 constrained by present-day means and trends
Example: Last Glacial Maximum
5-95%: 1.5K-5.8K
QUMP/PalaeoQUMP Simulations
Example: Last Glacial Maximum
5-95%: -0.4K-7.7K
QUMP/PalaeoQUMP Simulations
See also Schmidt et al. 2013 Clim. Past Discuss.
Quantitative use of Palaeoclimate Data in Constraining Projections
• Potentially large ‘signal’, perhaps correlated with things we might want to project• Also potentially large ‘noise’ arising from uncertainties in palaeo-reconstructions and uncertainties in forcings/boundary conditions• Three examples
• Natural variations in the El Niño Southern Oscillation• Pliocene• Joint constraints from Mid-Holocene and Last Glacial Maximum
© Crown copyright Met Office
El Niño Conditions(SST Anomalies)
thermocline
upwelling
El Niño Southern Oscillation (ENSO) Variability during the Last Millennium
Russon et al. submitted
Palmyra Atoll
Western Cold Tongue NINO3
El Niño Southern Oscillation (ENSO) Variability during the Last Millennium
Russon et al. submitted
Mid Pliocene Warm Period (3.3-3.0 million years BP)
• Characterised by high (natural) concentrations of CO2 (405 ppmv)• Continental configuration similar to present day• Palaeo reconstructions available from ocean sediments and plant fossils• Simulations with perturbed parameter versions of HadCM3 using PRISM2 boundary conditions (reduced Rockies, Greenland and Antarctica, vegetation changes)
James Pope
Temperature difference from STD
B
H
K
N
D
I
L
F
J
M
P Q
James Pope
Data-Model Comparison: TemperatureEnsemble Member B Standard Ensemble Member P
James Pope
Data-Model Comparison: Biomes
B J
P
James Pope
CONSTRAINTS FROM MID-HOLOCENE AND LGM
STATISTICAL MODEL
We want to make as few assumptions and judgements as possible
We don’t feel confident weighting simulators by their relative successso we use the ensemble
mean
don’t include multiple versions of same simulatorand check for outliers
We work with the large-scale patterns of change
Rougier, Goldstein and House (in review.): Second-order exchangeability analysis for multi-model ensembles. Journal of the American Statistical Association.
UPDATE CLIMATE SENSITIVITY
still watching this space
Edwards et al. in prep
Summary and Conclusions• Palaeo-data can be used in a quantitative way in climate science• The main issues are those of signal-to-noise and having the right simulations, observations and techniques• Three examples
• Reconstructions of ENSO show that the period of modern-day observations is quite anomalous in comparison with the previous 1000 years• Higher-sensitivity Pliocene simulations are more consistent with observations than lower sensitivity models • Statistical frameworks are required to synthesise models and data (just like they are for modern-day observations and simulations)
#RMetSMeet