Reconstruction of historical temperatures during the last millennium- analysis of methods- significance for detection of anthropogenic climate change

Hans von Storch & Eduardo ZoritaInstitute for Coastal ResearchGKSS Research Center, Germany

Fidel González-Rouco, Universidad Complutense, Madrid, Spain

Meeting #1 Open Session of Committee on Surface Temperature Reconstructions for the past 1,000-2,000 Years: Synthesis of Current Understanding and Challenges for the Future, Washington, 2.3.2006

Our results indicate …

The temperature variations during the preindustrial times (1000-1850) are likely considerably larger than shown by the “shaft” of the “hockeystick”.

The significance of the “blade” for detecting ongoing anthropogenic climate change is not compromised by the choice of the various historical reconstructions.

The debate has been unfortunate as …

• Premature declaration of validity of a knowledge claim;

• Critique stifled instead of encouraging debate and discussion to get a full airy for concern of misuse in the political process;

IPCC chairmann Pachauri in “nature”,

2005

Major conclusions should be

1. Peer review process: no publication without reproducible description of complex methodology;

2. IPCC and related processes: Have independent scientists doing the review; not the key authors in the field.

3. Data access: Relevant data and details of algorithms need to be made public even to “adversaries”.

"We have 25 or so years invested in the work. Why should I make the data available to you, when your aim is to try and find something wrong with it." (Jones' reply to Warwick Hughes, 21. Februar 2005; confirmed by P. Jones)

Our work

• Are the methods suggested by MBH98 and by Moberg 2005 reliable in returning unbiased estimates of low-frequency temperature variations?

• How good is the method of inverting terrestrial borehole temperature profiles?

• This is tested in the laboratory of a 1000 year simulation exposed to estimated natural and anthropogenic forcings.

Relevant new publications from our international and

interdisciplinary group● Zorita, E., and H. von Storch, 2005: Methodical

aspects of reconstructing non-local historical temperatures, Memorie della Società Astronomica Italia 76, p.794ff

● González-Rouco, J.F., H. Beltrami, E. Zorita, and H. von Storch, 2006: Simulation and inversion of borehole temperature profiles in surrogate climates: spatial distribution and surface coupling. Geophys. Res. Letters 33, doi:10.1029/2005GL024693

● Rybski, D., A. Bunde, S. Havlin,and H. von Storch, 2006: Long-term persistence in climate and the detection problem. Geophys Res. Lett. (in press)

Courtesy of Philip Brohan, Hadley Centre

Recent "global" near-surface air temperature anomalies

Comparison between simulations and real reconstructions

Not a specific result of ECHO-G

For the purpose of testing reconstruction methods, it does not really matter how „good“ the historical climate is reproduced by a millennial simulation.

Such model data provide a laboratory to test MBH, Moberg, borehole inversion and other methods as well as hypothesis like “McMc”.

Training with trend• In our test of MBH in science

(2004), the trend in the calibration period was taken out.

• When the trend during the calibration period is used as a critical factor in the empirical reconstruction model, then the contamination of the proxy trend by non-climatic signals must be mimicked.

• Thus, we introduced an error on the centennial time scale as red noise.

• Here: 50% centennial,75% year-to-year.

• Again heavy underestimation of long-term variability.

Claim: MBH was not built for such large variations as in Erik-I

But – the same

phenomenon emerges in a

control run.

Using trends in statistical modelling …

CPS: simple average of normalized proxies,

then rescale to instrumental NHT variance

Testing the Moberg method in the laboratory of ECHO-G. The inflation is done using 80-year filtered data.

Solid: Northern Hemisphere temperature simulated in ECHO-G

Light: Several reconstructions obtained when feeding Moberg's method with local temperature records, which have been contaminated with centennial noise (signal-to-noise ratio: 1)

Testing Moberg’s

method

Forward model simulations of borehole temperature profiles with SAT at all NH grid points (light shading) and at selected borehole grid points.

21 year low pass filter of SAT and inverted (forward modelled) borehole temperatures

González-Rouco et al., 2006, GRL

Testing the method of inverting borehole temps

We conclude

● MBH98 underestimates low-frequency variability.

● Moberg does a reasonable job (maybe fortuitously).

● Borehole temperatures reconstructions provide reasonable estimates, albeit heavily smoothed.

No sulfate aerosols

Does the controversy about the methodology in reconstructing historical temperature variations have a bearing on the claims that an anthropogenic signal is detectable in the recent temperature change?

NO

Historical Reconstructions – their significance for

“detection”

● - Statistics of ΔTL,m, which is the difference of two m-year temperature means separated by L years.

● - Temperature variations are modelled as Gaussian long-memory process, fitted to the various reconstructions.

Rybski, D., A. Bunde, S. Havlin,and H. von Storch, 2006: Long-term persistence in climate and the detection problem. Geophys Res. Lett. (in press)

Temporal development of Ti(m,L) = Ti(m) – Ti-L(m) divided by the standard deviation (m,L) of the considered reconstructed temp record

for m=5 and L=20 (top), andfor m=30 and L=100 years.

The thresholds R = 2, 2.5 and 3 are given as dashed lines.

Bunde et al., GRL, 2006, in press

From IPCC TAR (2001)

From Gerber, Joos, Brügger, Stocker, Mann, Sitch and Scholze, Climate Dynamics, 2003

The mystery of the expected errorof reconstruction

Rep. Boehlerts questions:

• What is the current scientific consensus on the temperature record of the last 1,000 or 2,000 years? What are the main areas of uncertainty and how significant are they?

• What is the current scientific consensus on the conclusions reached by Drs. Mann, Bradley and Hughes? What are principal scientific criticism of their work and how significant are they? Has the information needed to replicate their work been available? Have other scientists been able to replicate their work?

• How central is the debate over the paleoclimate temperature record to the overall consensus on global climate change? How central is the work of Drs. Mann, Bradley and Hughes to the consensus on the temperature record?

• There is consensus on the “blade”, but the claimed smoothness of the shaft is likely false.

• The main problem is the loss of information encoded in the proxy data and the shortness of the instrumental record for training the statistical models.

• There is no consensus on the claims (which?) made by MBH. The main critique is that the method is suffering from a too large loss of variability on long time scales.

• No, the information required for replication was not made available in a suitable manner. The original publication in “nature” did not provide this information and was obviously published without careful review of the methodology.

• Yes, the details of the method were finally determined, among others by Bürger et al., who checked a wide range of combinations of details – which all gave widely different results.

• The main conclusions about “detection and attribution” are drawn from the instrumental record and models; the different reconstructions do not contradict “detection”.

• The MBH work is widely accepted as truth outside of people directly engaged in the issue, because of a less than satisfactory marketing by the IPCC.

Additional relevant literature

Bürger, G., I. Fast, and U. Cubasch, 2006: Climate reconstruction by regression - 32 variations on a theme, Tellus 58A, 227-235.

Bürger, G., and U. Cubasch, 2005: Are multiproxy climate reconstructions robust? Geophs. Res. Lett. 32, L23711, doi:10.1029/2005GL024155

See also,

von Storch, H. and N. Stehr 2005: ● A Climate of Staged Angst,

http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/000343a_climate_of_staged_.html

● Et klima af iscenesat frygt. Vejret 10, 39-42● Geënsceneerede klimaatangst. Natuur, Wetenschap

& Techniek 73, 44-46● Klima inszenierter Angst. SPIEGEL 4/2005, 160-161

Reserve

Coupler(CERFACS Rep. CMGC/98-05, 1998)

•Coupling: 1 day•Atm Oce: Heat, fresh watter,

momentum fluxes•Oce Atm: Surface conditions•Grid interpolation

Ocean component(DKRZ Rep. 13, 1997)

•Prim. Eq. & Thermodyn.+ sea ice model with snow cover

•Gauss. T42 ~ 2.8 x 2.8 ºlat x ºlon 0.5 ºlat x ºlon Equator

•20 levels

Model descriptionModel description

GCM: ECHO-G

Atmospheric component(MPI Rep. 218, 1996)

•ECMWFMPI•~ECHAM3

+ fresh water on glaciers+ river runnoff + partial ice cover

•T30 ~ 3.75 x 3.75 ºlat x ºlon•19 vertical levels:

Highest: 10 hPa~ 30 kmLowest:~ 30 m

Soil modelSoil model

GCM: ECHO-G

Extension of

Warrilow et al., 1986 Met. Off. Tech. Note, 38.

T5=

T1=

T2=

T3=

T4=

Land-Sea Mask

T30 resolution

Soil processes:

T(z) soil

Snow pack

Soil hidrology

Z=0 m

0.065 m

0.319 m

1.232 m

4.134 m

9.834 m

• Forcing is not particularly strong

• Sensitivity of ECHO-G about 2.5K

Different reconstructions of solar irradiance

ECHO-G simulations „Erik den Røde” (1000-1990)

and “Christoph Columbus” (1550-1990)

with estimated volcanic, GHG and solar forcing

Man et al, 2005

Remind: only coarse stratosphere,no ozone (ECHO-G)

Discussion

Trend – does it really help ?