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Moberg, A. , Sonechkin, D. M. , Holmgren, K. , Datsenko, N. M. & Karlen, W. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature 433, 613-617


Abstract and Figures

A number of reconstructions of millennial-scale climate variability have been carried out in order to understand patterns of natural climate variability, on decade to century timescales, and the role of anthropogenic forcing. These reconstructions have mainly used tree-ring data and other data sets of annual to decadal resolution. Lake and ocean sediments have a lower time resolution, but provide climate information at multicentennial timescales that may not be captured by tree-ring data. Here we reconstruct Northern Hemisphere temperatures for the past 2,000 years by combining low-resolution proxies with tree-ring data, using a wavelet transform technique to achieve timescale-dependent processing of the data. Our reconstruction shows larger multicentennial variability than most previous multi-proxy reconstructions, but agrees well with temperatures reconstructed from borehole measurements and with temperatures obtained with a general circulation model. According to our reconstruction, high temperatures--similar to those observed in the twentieth century before 1990--occurred around ad 1000 to 1100, and minimum temperatures that are about 0.7 K below the average of 1961-90 occurred around ad 1600. This large natural variability in the past suggests an important role of natural multicentennial variability that is likely to continue.
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Highly variable Northern Hemisphere
temperatures reconstructed from
low- and high-resolution proxy data
Anders Moberg
, Dmitry M. Sonechkin
, Karin Holmgren
Nina M. Datsenko
& Wibjo
rn Karle
Department of Meteorology, Stockholm University, SE-106 91 Stockholm,
Dynamical-Stochastical Laboratory, Hydrometeorological Research Centre of
Russia, Bolshoy Predtechensky Lane 11/13, Moscow 123 242, Russia
Department of Physical Geography and Quaternary Geology, Stockholm
University, SE-106 91 Stockholm, Sweden
A number of reconstructions of millennial-scale climate varia-
bility have been carried out in order to understand patterns of
natural climate variability, on decade to century timescales, and
the role of anthropogenic forcing
. These reconstructions have
mainly used tree-ring data and other data sets of annual to
decadal resolution. Lake and ocean sediments have a lower
time resolution, but provide climate information at multicen-
tennial timescales that may not be captured by tree-ring data
Here we reconstruct Northern Hemisphere temperatures for the
past 2,000 years by combining low-resolution proxies with tree-
ring data, using a wavelet transfor m technique
to achieve
timescale-dependent processing of the data. Our reconstruction
shows larger multicentennial variability than m ost prev ious
multi-proxy reconstructions
, but agrees well with tempera-
tures reconstructed from borehole measurements
and with
temperatures obtained w ith a general circulation model
According to our reconstruction, high temperatures
to those obser ved in the twentieth centur y before 1990
occurred around AD 1000 to 1100, and minimum temperatures
that are about 0.7 K below the average of 1961–90 occurred
AD 1600. This large natural variability in the past suggests
an important role of natural multicentennial variability that is
likely to continue.
Global temperatures are currently rising, and future scenarios
suggest large changes in precipitation patterns and temperatures
Reconstructing past climate is essential for enhanced understanding
of climate variability, and provides necessary background knowl-
edge for improving predictions of future changes. From multi-
proxy combinations
of climate proxy data (for example, from
tree rings, corals and ice cores), or from reconstructions based solely
on tree-ring data
, past surface temperatures have been inferred
by calibration to instrumental temperature data using statistical
relationships. Past surface temperature changes have also been
inferred from temperature profiles along deep terrestrial bore-
, where physical laws rather than statistical relations are
used to estimate temperature trends. Borehole measurements
and some reconstructions based on tree-ring data
indicate a
larger warming trend in the past 500 yr than do multi-proxy
Although differences in the amplitude of centennial temperature
variability have been discussed in the literature
with relatively small variability (shown by multi-proxy reconstruc-
) is arguably best known by a wider audience. One reason
for this is the prominent role that the multi-proxy reconstruction by
Mann et al.
had in the latest IPCC report
and in public media.
Recent findings
, however, suggest that considerable underestima-
tion of centennial Northern Hemisphere temperature variability
may result when regression-based methods, like those used by
Mann et al.
, are applied to noisy proxy data with insufficient
spatial representativity. It is thus important to explore other
techniques and other data types, and also to use data from more
regions than previously examined.
A view has been expressed that only tree-ring and other high-
resolution data are useful for quantitative large-scale temperature
. Tree-ring data, however, have a well-documented
difficulty in reliably reproducing multicentennial temperature
. Special standardization techniques for extracting
multicentennial information exist
, but they do not ensure an
accurate reconstruction
. Natural archives with lower temporal
resolution (often various sediments) have potential for providing
climate information at multicentennial timescales that may not be
captured by tree-ring data
. Low-resolution data, on the other hand,
can sometimes have dating errors of up to more than 100 yr (ref. 9).
Such errors are intolerable at interannual to multidecadal time-
, but if these data are used only for longer timescales the errors
become relatively small in relation to the timescales of interest.
Our aim is to combine low-frequency climate information
(contained in low-resolution proxy data) with high-frequency
information (from tree-ring data) in order to derive a 2,000-yr-
long Northern Hemisphere temperature reconstruction in which we
avoid using each proxy type at timescales where it is most unreliable,
but instead use it only where it has its greatest advantages. To
achieve this, we developed a method that allows a timescale-
dependent data decomposition by application of a wavelet trans-
The number of available 2,000-yr-long local-to-regional scale
temperature proxy series is very limited
. We found seven tree-ring
series and eleven low-resolution proxy series. For the period before
AD 1400, this number is similar to previous reconstructions
Among the eleven low-resolution series were nine already calibrated
to local/regional temperatures for different Northern Hemisphere
regions, whereas two were only available in original proxy data
units. The data set includes climatic information from the North
American and Eurasian continents and from the Atlantic and Indian
oceans (Fig. 1, Table 1; see Supplementary Information for further
details and references).
Various averages (see Methods) of the nine already calibrated
low-resolution series (Table 1, site numbers 2–10) depict, when low-
pass filtered to highlight multicentennial variability (Fig. 2a), a
temperature maximum in the ninth or tenth centuries and a
Figure 1 Locations of proxy data sites. Shown are the locations of eleven low-resolution
proxy records (blue circles, numerals 1–11, see Table 1 for site details) and seven tree-
ring series (red triangles, letters A–G). Dashed latitude lines indicate the Equator, the
Tropic of Cancer and the Arctic Circle. See Supplementary Information for further details
and references.
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NATURE | doi:10.1038/nature03265 | 1
minimum in the sixteenth century, with a total range of 0.6 to 0.9 K.
This is a substantially larger multicentennial temperature range
compared to previous multi-proxy reconstructions
, exemplified
in Fig. 2a with the Northern Hemisphere reconstruction by Mann
and Jones
. The conflicting views provided by the low-resolution
series and this reconstruction illustrate a clear need for further
research to determine the size of natural low-frequency climate
Simple averages of temperature proxy series, such as those shown
in Fig. 2a, can yield adequate estimates of Northern Hemisphere
century-scale mean-temperature anomalies
. But to obtain a
reconstruction covering a complete range of timescales we created
a wavelet transform
, supposed to be approximately representative
for the Northern Hemisphere (Fig. 2e), such that only information
from the tree-ring records contributes to timescales less than 80 yr
and all eleven low-resolution proxies contribute only to the longer
timescales (see Methods for details). From the wavelet transform,
which was calculated using standardized (that is, unitless) proxy
series, a dimensionless reconstruction was obtained by calculating
the inverse wavelet transform
. Given the small number of tree-ring
series, their contribution is best thought of as an approximation
of the statistical character of variability at ,80-yr scales. A sample
size of eleven low-resolution series is reasonable for reconstructing
.80-yr variability, given that the number of spatial degrees
of freedom on the entire globe is about five at centennial time-
. The contribution from each low-resolution proxy series to
the total variance at .80-yr scales in the Northern Hemisphere
reconstruction is given in Table 1.
To calibrate the reconstruction, its mean value and variance
were adjusted to agree with the instrumental record of Northern
Hemisphere annual mean temperatures
in the overlapping period
AD 1856–1979 (Fig. 2b). This technique avoids the problem with
underestimation of low-frequency variability associated with
regression-based calibration methods
. Jack-knifed estimates
(light-blue curves in Fig. 2b) of the low-frequency component
(.80-yr scales, dark blue), where each of the eleven low-resolution
proxies are excluded one at a time, are all very similar, demonstrat-
ing that the reconstruction is robust to the omission of any single
low-resolution proxy series.
The reconstruction depicts two warm peaks around
AD 1000 and
1100 and pronounced coolness in the sixteenth and seventeenth
centuries, with an overall temperature range for the low-frequency
component (.80-yr scales) of about 0.65 K. This amplitude can be
compared with that in the smoothed and averaged low-resolution
series in Fig. 2a, where the data used had been calibrated to
temperatures by their original investigators. The size of the overall
amplitudes of the series in Fig. 2a (0.6–0.9 K) and Fig. 2b (0.65 K,
blue curve) indicates that the reconstructed multicentennial varia-
bility in Fig. 2b has not been inflated by the standardization, the
wavelet processing and the subsequent calibration technique. The
the twentieth century, although the post-1990 warmth seen in the
instrumental data (green curve in Fig. 2b) appears to be
Table 1 Summary information for low-resolution proxy series
No.* Site† Proxy type and
Dating type
(max. dating error)
last year
Sample resolution
(no. of samples)§
fraction (%) in
.80-yr scales
Proxyff NH{
1 Agassiz Ice Cap,
Ellesmere Island,
818 N, 738 W
Ice melt, layer stratigraphy,
summer T
Annual layer,
theoretical model,
ash layers (^10%)
29, 1961 5 (393) 2.4 0.3
2 GRIP borehole,
738 N, 388 W
Borehole T, annual T Theoretical model 2300, 1996 50 (40) 89.2 12.5
3 Conroy Lake,
Eastern US,
468 N, 688 W
Pollen, lake sediments,
summer T
Annual laminations 35, 1968 7–40 (68) 69.2 9.7
4 Chesapeake Bay,
Eastern US,
388 N, 768 W
Shells, Mg/Ca variation,
spring T
C(^160 yr),
Pb and
5, 1995 1–65 (427) 30.8 4.3
5 N. Sargasso Sea,
338 N, 578 W
annual SST
C(^160 yr) 2300, 1925 50–150 (30) 65.0 9.1
6 NE Caribbean Sea,
188 N, 678 W
annual SST
C(^200 yr) 133, 1950 30–160 (26) 99.6 14.0
7 Lake Tsuolbmajavri,
N. Finland,
688 N, 228 E
Diatoms, lake sediments,
summer T
C(^ 169 yr) 2300, 1950 ,70 (29) 61.5 9.9
8 Søylegrotta Cave,
Mo i Rana,
N. Norway,
668 N, 138 E
annual T
U(^46 yr) 2300, 1938 ,20 (103) 47.3 7.6
9 Shihua Cave,
Beijing, China,
408 N, 1168 E
Stalagmite, layer thickness,
summer T
Layer counting (^5 yr) 2300, 1985 1 (1985) 32.2 5.2
10 China, 20–428 N,
80–1308 E
Composite of 9 records,
annual T
Layer counting,
C(^200 yr)
0, 1990 10 (200) 89.8 14.5
11 Arabian Sea,
188 N, 588 E
% Globigerina bulloides,
up-welling, monsoons,
summer and winter T
C(^100 yr) 2300, 1986 15–180 (63) 78.6 12.7
*Numbered as in Fig. 1.
References and further site details are given in Supplementary Information.
T, temperature; SST, sea surface temperature.
#Negative numbers mean years before
AD 1.
§Sample resolution in years. Number of samples after year
AD 1 given in parentheses.
ff For each proxy, the fraction of its total variance that occurs in its .80-yr scales (wavelet scales 10–22, see Methods) is listed.
{For each proxy, its contribution (in %) to the total variance in the low-frequency component (wavelet scales 10–22) of the Northern Hemisphere (NH) temperature reconstruction is listed. These
contributions are determined by the values in the second to last column. The resulting contributions by data from different regions are geographically well distributed; Arctic 12.9, Eastern US 14.0,
Fennoscandia 17.6, China 19.7, Oceans 35.8. Furthermore, the five proxies that are annual mean temperature indicators (nos 2, 5, 6, 8, 10) together contribute 57.8% of the variance in the low-frequency
component of the NH reconstruction.
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Changes in radiative forcing due to variability in solar irradiance,
the amount of aerosols from volcanic eruptions and greenhouse gas
concentrations have been important agents causing climatic varia-
bility in the past millennium
. Reconstructions of the tem-
poral evolution of these variables have been used to drive climate
models, ranging from simple energy balance models to fully coupled
atmosphere–ocean general circulation models
Northern Hemisphere temperature series obtained from such an
experiment with the coupled model ECHO-G
for the AD
1000–1990 period (Fig. 2c) is qualitatively remarkably similar to our
multi-proxy reconstruction, although the model shows a somewhat
larger variability. Particularly strong qualitative similarity is seen at
timescales longer than centennial (compare the two wavelet trans-
form patterns, Fig. 2e, f), but some high-frequency details are also in
good agreement (for example, the double peaks around
AD 1000
and 1100, and two short cooling periods at
AD 1460 and 1820). The
model’s variability before the twentieth century is largely deter-
mined by the combined effects of the reconstructed solar and
volcanic forcing (that is, natural forcing) that was used in the
, whereas the notably strong warming in the model
data after
AD 1900 is largely due to rapidly increasing concentrations
of anthropogenic greenhouse gases
. The similarity between
our reconstruction and the ECHO-G model series supports the case
of a rather pronounced hemispheric low-frequency temperature
variability resulting from the climate systems response to natural
changes in radiative forcing.
As in all palaeoclimate reconstructions, there are uncertainties in
this one. Efforts to quantify uncertainties in the low-frequency
component are illustrated with blue bands of different colours in
Fig. 2d. Accounting for the total uncertainty, the cooling from the
maxima around
AD 1000 and 1100 to the minimum near AD 1600 is
between 0.3 K and 1.1 K for the .80-yr component. Only the
smallest value is similar to the corresponding temperature change
in previous multi-proxy reconstructions
. (Compare with the
reconstruction of Mann et al.
, which is also shown in Fig. 2d
(orange curve, yellow uncertainty range) after smoothing to show
.80-yr variability.) In contrast, the warming trend depicted by our
reconstruction in the past 500 yr is entirely consistent with estimates
of Northern Hemisphere ground surface temperature (GST) trends
from temperature measurements in nearly 700 boreholes
Although trends at individual borehole sites are very noisy, hemi-
spheric mean GST trends are robust to different aggregation and
Figure 2 Estimations of Northern Hemisphere mean temperature variations. a, Previous
multi-proxy reconstruction (MJ: from Mann and Jones
, black line) with ^2 s.d.
uncertainty (grey shading), and various averages (blue, green, magenta; see Methods) of
smoothed low-resolution temperature indicators (nos 2–10 in Table 1). b, Our multi-proxy
AD 1–1979 (red) with its .80-yr component AD 133–1925 (blue) and its
jack-knifed estimates (light blue), and the instrumental record
(green). c, Forced
ECHO-G model
. d, Low-frequency component of multi-proxy reconstruction in b
(blue curve) with confidence intervals for three separate uncertainties. The innermost
medium-blue band shows the uncertainty due to variance among the low-resolution proxy
series. The two outer bands show the uncertainty in the variance scaling factor (light blue)
and the constant adjustment (outermost blue band) separately. Each uncertainty is
illustrated with an approximate 95% confidence interval (see Supplementary Information).
Also shown are ground surface temperatures estimated from boreholes
with their
uncertainty interval (brown; see Methods), and the .80-yr component of a previous
multi-proxy reconstruction (MBH: from Mann et al.
, orange) with ^2 s.d. uncertainty
(yellow). e, f, Wavelet transform (see Methods) of the series in b and c where warm/cold
anomalies are red/blue. Temperature anomalies in a, b and d are with respect to the
1961–90 average.
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NATURE | doi:10.1038/nature03265 | 3
weighting schemes
(illustrated by the two brown curves in Fig. 2d),
and show a warming of ,1 K during the interval
AD 1500–2000, of
which about half fell in the twentieth century.
There are several reasons for the notable differences between our
and previous multi-proxy reconstructions. The reconstruction of
Mann and Jones
has a large amount of data in common with ours,
but these workers combined tree-ring data with decadally resolved
proxies without any separate treatment at different timescales.
Furthermore, our data set contains some centennially resolved
data from the oceans, while Mann and Jones used only annually
to decadally resolved data from continents or from locations very
near the coast. Different calibration methods (regression in the
work of Mann and Jones versus variance scaling in this study) are
another reason. Possible explanations for the small low-frequency
variability in the multi-proxy reconstruction of Mann et al.
recently been discussed in detail elsewhere
Our multi-proxy reconstruction achieves a relatively large multi-
centennial variability by separately considering the information in
tree-ring data and low-resolution proxy records. Much more effort,
however, is needed to develop new proxy data series and to
determine how proxy data should best be chosen, combined and
calibrated. The wavelet approach allows for separate weighting of
proxies at different timescales. A goal for further research could be
to determine how such weighting should be undertaken, while
simultaneously taking spatial representativity into account. New
experiments with distorted ‘pseudoproxy’ data
from forced
general circulation model runs, using various types of distortions,
should be useful in this context.
We find no evidence for any earlier periods in the last two
millennia with warmer conditions than the post-1990 period
agreement with previous similar studies
. The main implication
of our study, however, is that natural multicentennial climate
variability may be larger than commonly thought, and that much
of this variability could result from a response to natural changes in
radiative forcings. This does not imply that the global warming in
the last few decades
has been caused by natural forcing factors
alone, as model experiments that use natural-only forcings fail
to reproduce this warming
. Nevertheless, our ndings
underscore a need to improve scenarios for future climate
change by also including forced natural variability
which could
either amplify or attenuate anthropogenic climate change
significantly. A
Wavelet transformation
The wavelet transform
(WT) decomposes a time series into time–frequency space,
enabling the identification of both the dominant modes of variability and how those
modes vary with time. We used the Mexican hat
wavelet, after linear interpolation to
annual resolution, to decompose each proxy series into 22 wavelet ‘voices’. These are 22
separate time series, where each depict the variability in the original series at each of
the timescales near the Fourier periods 4, 4
2, 8, 8
2, …, 4,096
2 yr. This ranges
from the smallest possible scale for the Mexican hat wavelet up to a few times the
length of the 2,000-yr-long time interval of interest. Before calculating the WT, padding
with surrogate data to extend the proxy series from their last value to the year
AD 2300
was applied to limit boundary effects at the longest timescales. As padding data we
used the mean value for the last 50 yr with data in each series. For those records that do not
have data back at least to 300
BC, similar padding was also made at the beginning of
Averaging of calibrated low-resolution temperature indicators
Nine low-resolution proxy series (Table 1) are available as calibrated local/regional
temperature indicators (numbers 2–10). Five are annual mean (nos 2, 5, 6, 8, 10), one is a
spring (no. 4) and three are summer (nos 3, 7, 9) temperature indicators.
Multicentennial variability (highlighting .340-yr scales) in these series was extracted by
first applying the WT to each series and then the inverse WT only for wavelet voices 14–
22. Timescales of .340 yr are long enough to ensure that only information at frequencies
lower than the Nyquist frequency for the most poorly resolved proxy series are used.
Figure 2a shows arithmetic (green) and cos-latitude weighted (blue) averages of all nine
indicators. Jack-knifed estimates of the cos-latitude weighted averages, where each of the
nine indicators were removed one at a time, are also shown (magenta). These series are
plotted in Fig. 2a for the period
AD 133–1925 (when all have data) such that their mean
values agree with the Mann and Jones reconstruction
in the interval AD 200–1925.
Minor differences between the arithmetic and cos-latitude weighted series indicate
robustness to weighting choice. The similarity among the jack-knifed estimates indicates
that the overall temperature range is relatively little affected by the removal of any
individual indicator.
Timescale-dependent reconstruction
The multi-proxy reconstruction in Fig. 2b was constructed as follows. First, the data set of
19 proxy series in Fig. 1 was divided into two half-hemispheric subsets (western and
eastern half). After wavelet transformation of each individual proxy series into 22 voices as
described above (here using standardized series obtained by subtracting the mean and
dividing by the standard deviation, after linear interpolation to annual resolution), a
scale-by-scale averaging of wavelet voices was undertaken. For each wavelet scale from 1 to
9 (Fourier timescales ,80 yr), the voices from the individual tree-ring series were averaged
and, similarly, for each wavelet scale from 10 to 22 (Fourier timescales .80 yr) the
corresponding voices from the individual low-resolution proxy series were averaged.
Merging of the tree-ring-data average voices 1–9 with the low-resolution-data average
voices 10–22 gave one complete WT with voices 1–22 for each half-hemispheric subset.
The average of these two WTs then gave the whole-hemispheric WT shown in Fig. 2e.
The rationale for dividing into half-hemispheric subsets is similar to that used in
gridding; namely, to ensure that regions with many data series are weighted the same
as regions (of the same size) with few data series. However, for our data set, little
difference would be obtained if all data were placed in one whole-hemispheric set. A
dimensionless Northern Hemisphere temperature reconstruction was obtained by
calculating the inverse transform. Finally, this time series was calibrated by adjusting
its variance and mean value to be the same as in the instrumental data
in the
overlapping period
AD 1856–1979 (Fig. 2b). Separate estimates of uncertainties due to
variance among individual low-resolution proxy data and in the determination of the
variance scaling factor and constant adjustment term are explained in Supplementary
Plotting GST trends
The two curves for GST trends
shown in Fig. 2d correspond to the upper and lower
bounds for different area- and occupancy-weighted GST reconstructions, as illustrated in
figure 3 of ref. 12. To help visual comparison with our multi-proxy reconstruction, the
GST trends are plotted with reference to the
AD 1961–90 average in Fig. 2d. This was
achieved by shifting the GST trend-curves such that they cross the zero level at 1958.5,
which is the time when the twentieth century linear trend of the Northern Hemisphere
instrumental surface air temperature
(anomalies with respect to AD 1961–90) crosses the
zero level. (The same technique was used in figure 5 of ref. 12.)
Received 21 July; accepted 9 December 2004; doi:10.1038/nature03265.
1. Mann, M. E., Bradley, R. S. & Hughes, M. K. Global-scale temperature patterns and climate forcing
over the past six centuries. Nature 392, 779–787 (1998).
2. Mann, M. E., Bradley, R. S. & Hughes, M. K. Northern hemisphere temperatures during the past
millennium: Inferences, uncertainties, and limitations. Geophys. Res. Lett. 26, 759–762 (1999).
3. Jones, P. D., Briffa, K. R., Barnett, T. P. & Tett, S. F. B. High-resolution palaeoclimatic records for the
last millennium: interpretation, integration and comparison with General Circulation Model control-
run temperatures. Holocene 8, 455–471 (1998).
4. Crowley, T. J. & Lowery, T. S. How warm was the Medieval warm period? Ambio 29, 51–54
5. Briffa, K. R. Annual climate variability in the Holocene: interpreting the message of ancient trees.
Quat. Sci. Rev. 19, 87–105 (2000).
6. Esper, J., Cook, E. R. & Schweingruber, F. H. Low-frequency signals in long tree-ring chronologies for
reconstructing past temperature variability. Science 295, 2250–2253 (2002).
7. Mann, M. E. & Jones, P. D. Global surface temperatures over the past two millennia. Geophys. Res. Lett.
30, 1820, doi:10.1029/2003GL017814 (2003).
8. Jones, P. D. & Mann, M. E. Climate over past millennia. Rev. Geophys. 42, doi:10.1029/2003RG000143
9. Bradley, R. S. Paleoclimatology: Reconstructing Climates of the Quaternary (Academic, San Diego,
10. Esper, J., Frank, D. C. & Wilson, R. J. S. Climate reconstructions: Low-frequency ambition and high-
frequency ratification. Eos 85, 113 (2004).
11. Mallat, S. A Wavelet Tour of Signal Processing (Academic, San Diego, 1999).
12. Pollack, H. N. & Smerdon, J. E. Borehole climate reconstructions: Spatial structure and hemispheric
averages. J. Geophys. Res. 109, doi:10.1029/2003JD004163 (2004).
13. Gonza
lez-Rouco, F., von Storch, H. & Zorita, E. Deep soil temperature as a proxy for surface air-
temperature in a coupled model simulation of the last thousand years. Geophys. Res. Lett. 30, 2116,
doi:10.1029/2003GL018264 (2003).
14. von Storch, H. et al. Reconstructing past climate from noisy proxy data. Science 306, 679–682
15. Intergovernmental Panel on Climate Change. Climate Change 2001: The Scientific Basis (IPCC,
Geneva, 2001).
16. Briffa, K. R. et al. Low-frequency temperature variations from a northern tree ring density network.
J. Geophys. Res. 106, 2929–2941 (2001).
17. Cook, E. R., Briffa, K. R., Meko, D. M., Graybill, D. A. & Funkhouser, G. The ‘segment length curse’ in
long tree-ring chronology development for palaeoclimatic studies. Holocene 5, 229–237 (1995).
18. Jones, P. D., Osborn, T. J. & Briffa, K. R. Estimating sampling errors in large-scale temperature
averages. J. Clim. 10, 2548–2568 (1997).
19. Jones, P. D. & Moberg, A. Hemispheric and large-scale surface air temperature variations: An extensive
revision and an update to 2001. J. Clim. 16, 206–223 (2003).
20. Crowley, T. J. Causes of climate change over the past 1000 years. Science 289, 270–277 (2000).
NATURE 3265—27/1/2005—VBICKNELL—133809
letters to nature
NATURE | doi:10.1038/nature03265 |
21. Shindell, D. T., Schmidt, G. A., Mann, M. E., Rind, D. & Waple, A. Solar forcing of regional climate
change during the Maunder Minimum. Science 294, 2149–2152 (2001).
22. Bauer, E., Claussen, M., Brovkin, V. & Huenerbein, A. Assessing climate forcings of the Earth system
for the past millennium. Geophys. Res. Lett. 30, 1276, doi:10.1029/2002GL016639 (2003).
23. Bertrand, C., Loutre, M.-F., Crucifix, M. & Berger, A. Climate of the last millennium: a sensitivity
study. Tellus A 54, 221–244 (2002).
24. Shindell, D. T., Schmidt, G. A., Miller, R. L. & Mann, M. E. Volcanic and solar forcing of climate
change during the Maunder Minimum. J. Clim. 16, 4094–4107 (2003).
25. Zorita, E. et al. Climate evolution in the last five centuries simulated by an atmosphere-ocean model:
global temperatures, the North Atlantic Oscillation and the Late Maunder Minimum. Meteorol. Z. 13,
271–289 (2004).
26. Legutke, S. & Voss, R. The Hamburg Atmosphere-Ocean Coupled Circulation Model ECHO-G
(Technical Report 18, Deutsches Klimarechenzentrum, Hamburg, 1999).
27. Widmann, M. & Tett, S. F. B. Simulating the climate in the last millennium. PAGES News 11( 2&3),
21–23 (2003).
28. Mann, M. E. & Rutherford, S. Climate reconstruction using ‘Pseudoproxies’. Geophys. Res. Lett. 29,
1501, doi:10.1029/2001GL014554 (2002).
29. Zorita, E., Gonza
lez-Rouco, F. & Legutke, S. Testing the Mann et al. 1998 approach to paleoclimate
reconstructions in the context of a 1000-yr control simulation with the ECHO-G coupled climate
model. J. Clim. 16, 1378–1390 (2003).
30. Stott, P. A. et al. External control of 20th century temperature by natural and anthropogenic forcings.
Science 290, 2133–2137 (2000).
Supplementary Information accompanies the paper on
Acknowledgements We thank H. von Storch, E. Zorita and F. Gonza
lez-Rouco for the ECHO-G
data, and H. Pollack and J. Smerdon for borehole data. All these persons and J. Esper, J.
Luterbacher and M. Rummukainen are thanked for comments on early versions of the
manuscript. We acknowledge financial support from the Royal Swedish Academy of Sciences, the
Swedish Science Council and the Russian Foundation for Basic Research.
Competing interests statement The authors declare that they have no competing financial
Correspondence and requests for materials should be addressed to A.M.
NATURE 3265—27/1/2005—VBICKNELL—133809
letters to nature
NATURE | doi:10.1038/nature03265 | 5
... The generally lower abundance of deep water-adapted F. gyirongensis in Zones I (1180-1380 CE) and III (1940-2018 CE) indicated a low lake level, while the overall higher abundance in Zone II (1380-1940 CE) indicated a high lake level (Fig. 4). The time periods of Zones I, II, and III roughly correspond to the MWP, the LIA and the CWP, respectively (Moberg et al., 2005) (Fig. 8i). Therefore, our record showed that the water level of Dalongchi Lake was lower during the MWP and CWP and was higher during the LIA. ...
... (h) The synthesized moisture curve in ACA (Chen et al., 2010). (i) Temperature anomalies in the Northern Hemisphere (Moberg et al., 2005). Light gray bars highlight intervals of increased humidity in Lake Dalongchi over the last millennium. ...
... Assuming that warming also occurred at twice the rate of the global average at the end of the LIA, the TP temperature would have increased by 1.6 C. This remarkable warming is also reflected in the d 18 O records of the Dasuopu ice core, which increased significantly from À22‰ to À18‰ (Fig. 6c), albeit, with a certain temporal bias, possibly due to the dating errors arising from different climatic proxy media (Moberg et al., 2005). During this period, the precipitation was comparable to the LIA maximum (Fig. 6b). ...
... Widespread Buddhism in the Gannan region began with the anti-Buddhism campaign carried out by the last Zanpu (the honorific title of the Rulers of Tubo) of Tubo, Gldarma, after his succession in the mid-9th century, which forced many monks to flee to the Amdo region (Gannan Tibetan Autonomous Prefecture Local Chronicles Compilation Figure 4 Variations in BC concentration in Lake Dalzong and regional natural climatic context. (a) Pollen percentage of Xing Co, Zoige ; (b) precipitation over the past millennium based on tree-ring reconstruction at five sites in the northeastern Tibetan Plateau (Gou et al., 2014); (c) temperature reconstruction in the Northern Hemisphere (Moberg et al., 2005); (d) BC concentration at Lake Dalzong (the thin gray line is the raw data and the thick black line is the data smoothed over 50 years) and historical population changes in Gansu Province (Zhao and Xie, 1988). The thick lines in (a)-(c) are smoothed for 100 years. ...
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The ecological environment of the Tibetan Plateau, known as the “Third Pole of the Earth”, is extremely sensitive and fragile. With rapid societal development, environmental problems on the Tibetan Plateau have become prominent, as it is downwind of the emission sources from densely populated areas in the Middle East and South Asia, and the plateau has become one of the regions significantly affected by transboundary pollutant transmission (including black carbon, BC). The Tibetan Plateau has a long history of life and religious sacrifices, including aromatic plant-burning, which were recorded in the geologic record; therefore, BC can be used as a potential indicator to study the changes in religious activities. In this study, BC analysis was carried out based on the plausible dating framework tested by the AMS 14C and 137Cs methods on successive sediment cores from Lake Dalzong, an alpine lake in the Gannan Tibetan Autonomous Prefecture, northeast of the Tibetan Plateau. It was found that the BC in the lake sediments mainly accumulated through proximity wet deposition, and its content changes reflected the prevalence of surrounding religious activities. The study results indicate that the area of Lake Dalzong has experienced three periods of enhanced religious activities in the last millennium: 1490–1565 CE (mid-Ming Dynasty), 1810–1890 CE (late Qing Dynasty), and 1920 CE to the present (since the founding of the Republic of China), and the increase in religious activities on this centennial time scale is a response to concurrent social development. This study is the first to extract information on the variation in religious activities from lake sediments on the Tibetan Plateau, which will help advance the study of the historical context of the Anthropocene on the Tibetan Plateau.
Mediterranean environments are biodiversity hotspots in which strongly seasonal winter rainfall regimes and fire play major roles in driving ecosystem dynamics. Global predictions forecast unreliability of winter rainfall and increases in summer rainfall that are expected to result in major changes in community structure. Mediterranean systems are difficult to model, and although ecophysiological responses can be studied at observational timescales, a long-term understanding is necessary to address uncertainties and refine predictive models at landscape scales. Here we provide a ~ 1100 year-long palaeoecological reconstruction of vegetation (palynology), fire (sedimentary charcoal) and sedimentological change at a site adjacent to a multi-annual rainfall manipulation experiment designed to test plant population and community responses to altered seasonal regimes in the Greater Cape Floristic Region hotspot (southwestern Africa). We use these data to test whether long-term vegetation dynamics are controlled by changes in rainfall seasonality. We conclude that vegetation dynamics correlate with centennial-scale seasonality fluctuations, with transitions between two ecologically distinct fine-leaved shrub communities. These transitions are consistent with results of responses to experimental manipulations of summer rainfall. This study demonstrates the value of ecophysiological research in interpreting palaeoecological reconstructions and scaling up the results of observational research to answer long-term questions about environmental change.
The earth is getting warmer all the time. We feel this not only in our own bodies. Measurements at various locations all show a similar picture as in Fig. 2.1.
Sedimentary records of past tropical cyclone (TC) activity indicate large variability and spatial heterogeneity on the interannual-century scales. However, the meridional variation patterns and climatic forcing mechanisms for regional TC activity are not well understood because of the short and incomplete observational record. Here, we present a near-annually resolved record of intense TC activity derived from a back-reef lagoon at Anle Atoll in the southern South China Sea since the Little Ice Age (LIA). Our reconstruction indicates that TC activity was higher during the early LIA than what has been observed throughout the instrumental record. Basin-wide compiled records of the western North Pacific (WNP) cyclogenesis revealed strong evidence of a meridional seesaw pattern for storm activity between relatively low and high latitudes over the past millennium. This pattern suggests a centennial-scale link with Pacific hydroclimate atmospheric circulation shifts. A combination of southward displacement of the Intertropical Convergence Zone and westward migration of the Pacific Walker Circulation, as well as damped El Niño Southern Oscillation variability, likely contributed to enhanced TC activity during the LIA in the low latitudes of the WNP. External forcing of solar irradiance budgets profoundly affects the hydroclimate and TC climatology in the WNP.
Rainfall in the Asia summer monsoon (ASM) domain has a complex spatial pattern with the temporal variability at different timescales and their long‐term change has not been fully characterized. An updated 320 multi‐proxies network is used to reconstruct the May‐October precipitation during the past millennium for eight regions in the ASM domain. The spatial consistency of summer monsoon precipitation variability and the possible links to the internal climate oscillations are investigated. The results show that the regional precipitations over the last millennium in the ASM regions are dominated by the inter‐annual cycle of 2‐5a, the decadal cycle of ~11a and 15‐25a, and the multi‐decadal cycle of ~30a and 40‐80a. Coherent dry decades in different regions appear in 1100‐1250, 1600‐1650 and 1960‐2000, while the wet decades appear in 970‐990, 1330‐1350, 1380‐1430, 1550‐1580, 1700‐1780 and 1810‐1910. On inter‐annual scale, the relationships between precipitation for each region and El Niño/Southern Oscillation (ENSO) in both developing and decaying stages are unstable over the entire millennium, but they have opposite‐sign correlations most of the time, which implies that the summer precipitation anomaly for a region tends to reverse in the next summer when a strong ENSO event occurs in the winter. For the long‐term change from multi‐decadal to centennial scales, the longest dry period of the 12th to 13th centuries in eastern Asia coincides with the period with the lowest ENSO variability due to the in phase change of the Atlantic Multi‐decadal Oscillation and the Pacific Decadal Oscillation, which could result in the neutral inter‐basin east‐west cell in tropics and low frequency of ENSO events. This article is protected by copyright. All rights reserved.
Climate change and clean energy challenges are the joint subjects of this paper. We used the 1800–2020 anomalies time series in CO2 atmospheric concentration, in global mean surface temperature and on energy consumption to search for eventual periodic structures underlying multi-logistic model trend function for these parameters. Fourier analysis of model-to-data residues time series disclosed harmonic rhythms whose periods were entirely compatible economic cycles of the type of generational Kuznets infrastructure changes and Kondratiev radical technological innovation substitution. Historical data is used to demonstrate that along the last two centuries the atmospheric carbon dioxide concentration and global mean surface temperature anomalies are linearly correlated. For 2066, we forecast a global mean surface temperature anomaly of about 1.9 °C and 480.7 ppm for the atmospheric carbon dioxide concentration. Elaborating on Kuznets plots for primary energy consumption, we forecast that by 2037 mankind is most likely to enter a new period, namely, the Green Energy Revolution, meaning that the challenge for clean energy may eventually be won.KeywordsEnergyClimateGlobal surface temperatureLogistic modelSustainabilityEnergetics evolution
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Quantifying the marine radiocarbon reservoir effect, offsets (ΔR), and ΔR variability over time is critical to improving dating estimates of marine samples while also providing a proxy of water mass dynamics. In the northeastern Pacific, where no high-resolution time series of ΔR has yet been established, we sampled radiocarbon ( ¹⁴ C) from exactly dated growth increments in a multicentennial chronology of the long-lived bivalve, Pacific geoduck ( Paneopea generosa ) at the Tree Nob site, coastal British Columbia, Canada. Samples were taken at approximately decadal time intervals from 1725 CE to 1920 CE and indicate average ΔR values of 256 ± 22 years (1σ) consistent with existing discrete estimates. Temporal variability in ΔR is small relative to analogous Atlantic records except for an unusually old-water event, 1802–1812. The correlation between ΔR and sea surface temperature (SST) reconstructed from geoduck increment width is weakly significant (r ² = .29, p = .03), indicating warm water is generally old, when the 1802–1812 interval is excluded. This interval contains the oldest (–2.1σ) anomaly, and that is coincident with the coldest (–2.7σ) anomalies of the temperature reconstruction. An additional 32 ¹⁴ C values spanning 1952–1980 were detrended using a northeastern Pacific bomb pulse curve. Significant positive correlations were identified between the detrended ¹⁴ C data and annual El Niño Southern Oscillation (ENSO) and summer SST such that cooler conditions are associated with older water. Thus, ¹⁴ C is generally relatively stable with weak, potentially inconsistent associations to climate variables, but capable of infrequent excursions as illustrated by the unusually cold, old-water 1802–1812 interval.
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[1] We present reconstructions of Northern and Southern Hemisphere mean surface temperature over the past two millennia based on high-resolution ‘proxy’ temperature data which retain millennial-scale variability. These reconstructions indicate that late 20th century warmth is unprecedented for at least roughly the past two millennia for the Northern Hemisphere. Conclusions for the Southern Hemisphere and global mean temperature are limited by the sparseness of available proxy data in the Southern Hemisphere at present.
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Introduction Climatic changes during the last thousand years have received great interest. Uncertainty in climate reconstruction is smaller than in earlier periods and the external forcing factors of the climate system are relatively well known, making comparisons with 20th century climate well suited to assess the influence of human activities. Numerical modelling complements the efforts to reconstruct past climates from proxy records. The goals of climate modelling are to reduce uncertainties in future climate change through consistency tests with empirical reconstructions, to provide hypotheses on the climatic evolution at locations or variables not covered by proxy data, and to improve process understanding, including distinguishing between internal variability and the effects of varying external forcings, and understanding feedback mechanisms.
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This study is an extensive revision of the Climatic Research Unit (CRU) land station temperature database that is used to produce a gridbox dataset of 5° latitude × 5° longitude temperature anomalies. The new database comprises 5159 station records, of which 4167 have enough data for the 1961-90 period to calculate or estimate the necessary averages. Apart from the increase in station numbers compared to the earlier study in 1994, many station records have had their data replaced by newly homogenized series that have been produced by several recent studies. New versions of all the gridded datasets currently available on the CRU Web site ( have been developed. This includes combinations with marine (sea surface temperature anomalies) data over the oceans and versions with adjustment of the variance of individual gridbox series to remove the effects of changing station numbers through time.Hemispheric and global temperature averages for land areas developed with the new dataset differ slightly from those developed in 1994. Possible reasons for the differences between the new and the earlier analysis and those from the National Climatic Data Center and the Goddard Institute for Space Studies are discussed. Differences are greatest over the Southern Hemisphere and at the beginnings and ends of each time series and relate to gridbox sizes and data availability. The rate of annual warming for global land areas over the 1901-2000 period is estimated by least squares to be 0.07°C decade1 (significant at better than the 99.9% level). Warming is not continuous but occurs principally over two periods (about 1920-45 and since 1975). Annual temperature series for the seven continents and the Arctic all show significant warming over the twentieth century, with significant (95%) warming for 1920-44 for North America, the Arctic, Africa, and South America, and all continents except Australia and the Antarctic since 1977. Cooling is significant during the intervening period (1945-76) for North America, the Arctic, and Africa.
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We test the performance of proxy-based climate field reconstruction methods using sets of synthetic proxy climate indicators. `Pseudoproxies' are constructed through the degradation of instrumental surface temperature data by additive noise with variable statistical properties. Experiments are performed using pseudoproxy networks of varying spatial and seasonal representation and with varying noise attributes. Implications for sampling strategies for improved paleoclimate reconstructions are discussed.
A frequent conclusion based on study of individual records from the so-called Medieval Warm Period (~1000-1300 A.D.) is that the present warmth of the 20th century is not unusual and therefore cannot be taken as an indication of forced climate change from greenhouse gas emissions. This conclusion is not supported by published composites of Northern Hemisphere climate change, but the conclusions of such syntheses are often either ignored or challenged. In this paper, we revisit the controversy by incorporating additional time series not used in earlier hemispheric compilations. Another difference is that the present reconstruction uses records that are only 900-1000 years long, thereby, avoiding the potential problem of uncertainties introduced by using different numbers of records at different times. Despite clear evidence for Medieval warmth greater than present in some individual records, the new hemispheric composite supports the principal conclusion of earlier hemispheric reconstructions and, furthermore, indicates that maximum Medieval warmth was restricted to two-three 20-30 year intervals, with composite values during these times being only comparable to the mid-20th century warm time interval. Failure to substantiate hemispheric warmth greater than the present consistently occurs in composites because there are significant offsets in timing of warmth in different regions; ignoring these offsets can lead to serious errors concerning inferences about the magnitude of Medieval warmth and its relevance to interpretation of late 20th century warming.
We describe new reconstructions of northern extratropical summer temperatures for nine subcontinental-scale regions and a composite series representing quasi "Northern Hemisphere" temperature change over the last 600 years. These series are based on tree ring density data that have been processed using a novel statistical technique (age band decomposition) designed to preserve greater long-timescale variability than in previous analyses. We provide time-dependent and timescale-dependent uncertainty estimates for all of the reconstructions. The new regional estimates are generally cooler in almost all precalibration periods, compared to estimates obtained using earlier processing methods, particularly during the 17th century. One exception is the reconstruction for northern Siberia, where 15th century summers are now estimated to be warmer than those observed in the 20th century. In producing a new Northern Hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data, and the reliability of each regional series, begins to decrease. We compare our new hemisphere series to other published large-regional temperature histories, most of which lie within the 1σ confidence band of our estimates over most of the last 600 years. The 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period.