download

Contributions of Natural and Anthropogenic
Forcings in Twentieth-Century Temperature Change:
Results from the FGOALS_gl Coupled Model
Wenmin MAN, Tianjun ZHOU
Email: manwenmin@mail.iap.ac.cn
C20C, Beijing, Oct. 26, 2010
National Key Laboratory of Numerical modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG),
Institute of Atmospheric Physics (IAP),Chinese(
Academy of Sciences (CAS)

Outline
1. Background & motivation
2. Model & experiments
3. Results
4.Conclusions

Background
• A project entitled “Numerical simulation of the last millennial
climate change over China”, as one part of a NSFC Major
Program entitled “Tree Ring and Millennial Climate Change
Research in Chinese Domain”, granted by the National
Natural Science Foundation of China (NSFC).
• Motivation:
How well does the model simulate the 20 th century warming

Motivation
increasing GHG
concentrations
Three factors
could contribute
to the 20th
century warming
solar irradiance and
volcanic activities
natural internal climate
variability
The purpose of the present study is to evaluate the contributions of natural and
anthropogenic forcings in the 20th century temperature change from the coupled
climate model developed at LASG/IAP.

Framework of FGOALS_gl
1*1 L30
LICOM
Ocean
Atmosphere
GAMIL (Low)
(5*4 L26)
Coupler
Sea-ice
Land
5
Zhou et al. 2007, AAS

Experiments
Forcing data
All‐Forcing
(ALL)
1881‐2004yr
Natural‐Forcing
(NAT)
1881‐2004yr
natural forcings: solar radiation、volcanic aerosols
anthropogenic forcings: greenhouse gases、
tropospheric sulfates
natural forcings: solar radiation、volcanic aerosols
Without the inclusion of anthropogenic forcings
We use the HadCRUT3v observed surface temperature data to validate the
model results.
6

Global annual mean temperature series for the observation
and model historical forcing run
first warming
around the 1940s
recent warming
after the 1970s
Natural-forcing experiment clearly fails to reproduce the strong warming in the late
twentieth century, although natural forcings appear to contribute significantly to the early
twentieth-century warming.

Global mean surface temperature trends during three typical time
periods over 1910‐1999yr
OBS(℃/30a) ALL(℃/30a) NAT(℃/30a)
1911‐1940 0.36 0.29 0.26
1941‐1970 ‐0.07 ‐0.02 ‐0.15
1971‐2000 0.48 0.34 0.06
The warming of the early 20 th century could have resulted from natural forcings, however,
anthropogenic forcings have played an important role on the later 20th century global warming.
8

Surface temperature trends over the past 50yr and over the
20th century (℃ per 100yr)
‣Pronounced warming are seen
over many northern middle- and
high-latitude continental regions
and a broad region of more gradual
warming seen over the Indian
Ocean, Australia, the eastern
tropical Pacific, and South Atlantic.
‣Observed warming trends are
simulated realistically in the allforcing
run.
‣Natural-only forcing run shows
cooling trend in most regions.

Definition of sub‐regions
Northern
Extratropics
North
Pacific
U.S.
U.S.
U.S.
North
Atlantic
China
China
North
Pacific
Tropical East
Pacific
Indian Ocean/Western
Pacific Warm Pool
Indian Ocean/Western Pacific
Warm Pool
Tropics
Southern
Extratropics

Land‐ and hemispheric‐ scale surface temperature evolutions
The warming on the land- and hemispheric- scale in the all-forcing experiment generally
parallels the global average, also with the natural-forcing run fails to reproduce the strong
warming in the last half of the century.

Regional‐scale surface temperature evolutions
The warming signal has emerged rather monotonically in the Indian Ocean/western Pacific
region during the past century.
The tropical eastern Pacific、North Pacific and North Atlantic are regions where the
warming signal appears to emerge from a background of more substantial multidecadal
variability.

Contributions of natural and anthropogenic forcings
—expressed by ratio of explainable variance
Globalland
Globalocean
Northern
extratropics
Southern
extratropics
Indian
Ocean/Western
Pacific Warm Pool
Tropical
Eastern
Pacific
N.
Pacific
N.
Atlantic
NAT 7.4% 1.6% 27.3% 26.1% 1.1% 0.4% 8.0% 18.9%
Athro 76.6% 70.2% 61.5% 48.0% 76.7% 41.1% 47.2% 6.5%
For land and hemispheric means, external forcings could explain most of the variance.
Contributions from internal variability are larger than from external forcings in the tropical
eastern Pacific and North Atlantic region .
13

Annual mean temperature series over China
The reproducibility of the SAT averaged over China is lower than that of the global and
hemispheric averages, but it is still acceptable.
The model could not successfully produce the reconstructed warming over China in the 1920s.

Observed and simulated surface temperature trends over
China (℃ per 100yr)
‣All-forcing experiment
could generally reproduce
the warming trend over
East China.
‣Natural-forcing run
shows cooling trend over
East China.

Seasonal evolution of surface temperature trends over East
China during the last 50 years
warming trend
in DJF &MAM
cooling trend
in JJA

Conclusions
1) The simulations support previous findings that twentieth-century global
warming has resulted from a combination of natural and anthropogenic
forcing, with anthropogenic forcing being the dominant cause of the
pronounced late twentieth-century warming.
2) For global and hemispheric means,external forcings could explain most
of the variance. Contributions from internal variability are larger than from
external forcings in the tropical eastern Pacific and North Atlantic region,
where internal variability may dominate.
3) The reproducibility of the SAT averaged over China is lower than that of the
global and hemispheric averages, but it is still acceptable..

Zonal mean surface temperature changes over 1881‐2004yr

Global average SAT in CMIP3 Models
Cor=0.87
Zhou and Yu, 2006, J. Climate