NOAA Attribution Team Discussion Tom Knutson

1
NOAA Attribution Team DiscussionTom Knutson

• SST century-scale trends and low-frequency
  variability Comparisons of models and
  observations

2
Global Temperature Attribution
9
Observations

• are observed changes consistent with
• expected responses to forcings
• inconsistent with alternative explanations

All forcing
Solarvolcanic
Source IPCC 4th Assessment Report. Used with
permission.
3
Standard deviation of detrended annual mean
surface temperature (oC) vs. observed.
Observed (HadCRUT2v)
GFDL CM2.0 coupled model
GFDL CM2.1 coupled model
4
Surface Temperature Trends Assessment 1901-2000
(All Forcings Runs, GFDL CM2.0/2.1)
Black regions insignificant trend compared to
control run variability.
a) Observed Trend (1901-2000) HadCRUT2v data

b) Observed Trend Assessment vs. Control Runs
Colors significant trend compared to control
run variability

c) All-Forcings Ensemble Mean Trend (n8)
d) All-Forcings Assessment

Colors indicate significant difference
(model-obs).
White regions sparse data
Black regions no significant difference between
observed and modeled trends.
Reference Knutson et al. (2006). J. Climate.
5
Surface Temperature Trends Assessment 1901-2000
(Natural Forcings Only Solar and Volcanic)
a) Observed Trend (1901-2000)
b) Observed Trend Assessment vs. Control Runs

c) Natural Forcings Ensemble (n4)

d) Natural Forcings Assessment
c) All-Forcings Ensemble (n8)
d) All-Forcings Ensemble Assessment

6
Surface Temperature Trends Assessment 1901-2000
(Anthropogenic Forcings Only)
b) Observed Trend Assessment vs. Control Runs
a) Observed Trend (1901-2000)

d) Anthropogenic Forcings Assessment
c) Anthropogenic Forcings Ensemble (n4)

c) All-Forcings Ensemble (n8)
d) All-Forcings Ensemble Assessment

7
Surface Temperature Trends Assessment 1901-2000
(Comparison of Forcing Scenarios)
a) Internal Climate Variability Assessment

c) All-Forcings Ensemble
Assessment

b) Natural Forcings Ensemble
Assessment
d) Anthropogenic Forcings Ensemble
Assessment
Note Black regions denote areas of relative
agreement with observed trends.
Summary Runs including anthropogenic forcings
show closer agreement with observations.
8
Uncertainties in century-scale tropical SST
trends due to observational uncertainties
NOAA ERSST HadISST v
2.0 LDEO Kaplan SST v 2.0
Source Gabriel A. Vecchi Brian J. Soden,
Nature 450, 1066-1070 (13 December 2007)
doi10.1038/nature06423
9
Time series from selected regions Model vs.
Observations
10
Large-scale Tropical Indices
CM2.1 Ensemble Means
CM2.0 All Forcings
CM2.1 All Forcings
Tropics (20oN-20oS)
oC
Indian Ocean/Western Pacific Warm Pool
oC
Year
11
Large-scale Tropical Indices, contd.
CM2.1 Ensemble Means
CM2.0 All Forcings
CM2.1 All Forcings
Tropics (20oN-20oS)
oC
Eastern Tropical Pacific (20oN-20oS)
oC
Year
12
Large-scale Tropical Indices, contd.
CM2.1 Ensemble Means
CM2.0 All Forcings
CM2.1 All Forcings
Tropics (20oN-20oS)
oC
Tropical N. Atlantic Main Development Region
(10oN-20oN)
oC
Year
13
A key formation region for Atlantic hurricanes
14
11
What type of SST anthropogenic signal should we
look for in the tropical Atlantic?
Anthropogenic forcing Linear trend-like, but
the caveat of no indirect aerosol forcing yet.
Natural Anthropogenic forcing
Volcanic/solar/anthropogenic forcing gives a
closer fit to observations Residual (blue
black) AMO??
Sources Vecchi and Knutson, J. Climate, 2008.
See also Knutson et al. J. Climate, 2006
15
CM2.1 Ensemble Means
CM2.0 All Forcings
CM2.1 All Forcings
North Atlantic (45o-65oN)
oC
Tropical N. Atlantic Main Development Region
(10oN-20oN)
oC
16
CM2.1 Ensemble Means
CM2.0 All Forcings
CM2.1 All Forcings
Subtropical North Atlantic (10oN-45oN)
oC
Tropical N. Atlantic Main Development Region
(10oN-20oN)
oC
17
(No Transcript)
18
Possible extensions to the gridpoint based
assessment

• Update models and obs. to 2007 (A1B forcing
  scenario?)
• Use other models besides GFDL. May not have
  through 2007 or indiv. forcing runs
• Arbitrary start/end years
• Flexible season specification (2-month seasons)
• Precip as well as sfc temperature?
• Multiple observed data sets
• Ability to rate models and exclude models (e.g.,
  excessive surface temperature variability)
• Combine control runs from multiple models
  (adjustments for drift)
• Drift assessment/removal for forced runs
• Ability to focus on specified subregion of the
  world for maps display and/or time series display
  (e.g., targeted look at Southeast U.S.
  temperature issue)
• Web-based interface to allow user to specify and
  display results using optional analysis
  parameters or pre-build extensive set

19
Global Mean Surface Temperature Simulations
1870-2000
a) CM2.1 All Forcings
c) CM2.1 Anthropogenic Forcings
Krakatau eruption
b) CM2.1 Natural Forcings
20
Surface Temperature Trends Assessment 1949-2000
(All Forcings)
Black regions denote areas where the given model
simulates observed trends relatively well.
a) Observed Trend (1949-2000)

b) Observed Trend Assessment vs. Control Runs


c) All-Forcings Ensemble Mean Trend (n8)
d) All-Forcings Assessment

White regions sparse data
21
Surface Temperature Trends Assessment 1949-2000
(Comparison of Forcing Scenarios)
a) Internal Climate Variability Assessment

c) All-Forcings Ensemble
Assessment

b) Natural Forcings Ensemble
Assessment
d) Anthropogenic Forcings Ensemble
Assessment
Note Black regions denote areas of relative
agreement with observed trends.
Summary Runs including anthropogenic forcings
show closer agreement with observations.
22
Region definitions for time series plots
Alaska
Northern Asia
North Atlantic
Northern Extratropics
Rest of U.S.
S.E. U.S.
Subtropical North Atlantic
North Pacific
North Pacific
South Asia
Tropics
Indian Ocean/Western Pacific Warm Pool
Tropical North Atlantic
Tropical East Pacific
Southern Extratropics
23
Global Mean Surface Temperature Comparisons
CM2.0 All Forcings
CM2.1 All Forcings
CM2.1 Ensemble Means
oC
Year
Note All time series are 10-yr running means,
anomalies relative to 1881-1920 mean.
24
Northern vs. Southern Hemisphere Extratropics
CM2.1 Ensemble Means
CM2.0 All Forcings
CM2.1 All Forcings
Northern Hemisphere Extratropics (20oN-90oN)
oC
Southern Hemisphere Extratropics (20oS-90oS)
oC
Year
25
CM2.1 Ensemble Means
CM2.0 All Forcings
CM2.1 All Forcings
Southeast U.S.
oC
Rest of Continental U.S. (outside of Southeast
U.S.)
oC
26
CCSP 3.3 Findings

• Human-induced warming has likely caused much of
  the average temperature increase in North America
  over the past 50 years. This affects changes in
  temperature extremes.
• Heavy precipitation events averaged over North
  America have increased over the past 50 years,
  consistent with the observed increases in
  atmospheric water vapor, which have been linked
  to human-induced increases in greenhouse gases.

Question
What can/should NOAAs Climate Attribution Team
say beyond these findings?
27
Southeastern U.S. Regional Temperatures (Jan-Oct
1900-2008)
Source NCDC http//www.ncdc.noaa.gov/oa/climat
e/research/cag3/se.html
28
Summary

• Ensembles with anthropogenic forcing have global
  and regional trends generally in closer agreement
  with observations than runs using only natural
  forcings.
• Regional findings for United States
• Southeast U.S. cool period during 1960s and 1970s
  is not well captured by the model. Slight
  cooling trend since 1900.
• Rest of continental U.S. is in reasonable
  agreement with the model warming since 1900
  with substantial multi-decadal variability.

29
Summary of Radiative Forcings (1860-2000)
All-Forcings Runs include time varying

• Greenhouse gases (CO2, halocarbons, ozone, etc.)
• Anthropogenic tropospheric sulfates (direct
  effect only)
• Black and organic carbon
• Volcanic aerosols (Natural)
• Solar irradiance (Natural)
• Land cover type distribution

30
Summary of Radiative Forcings (1860-2000)
Natural-Forcing Runs include time varying

• Volcanic aerosols
• Solar irradiance (Lean et al.)

31
Summary of Radiative Forcings (1860-2000)
Anthropogenic-Forcings Runs include time varying

• Greenhouse gases (CO2, halocarbons, ozone, etc.)
• Anthropogenic tropospheric sulfates (direct
  effect only)
• Black and organic carbon
• Land cover type distribution

32
Understanding and Attributing Climate Change

• Continental warming
• likely shows a significant anthropogenic
  contribution over the past 50 years

Source IPCC 4th Assessment Report. Used with
permission.