Climate Change: Why Worry?

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Climate Change Why Worry?

Anji Seth, University of Connecticut
Primer Seminario de Investigación SANREM CRSP
Adaptación al Cambio en los Andes. La Paz, 24-28
Abril, 2006
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F.A.Q.

• How do we know climate is changing?
• Doesnt climate change naturally?
• So whats the deal with Global Warming?
• Cant we wait to see what happens?
• Warmer temperatures would be kind of nice?

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How do we know climate is changing?
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Austria
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FIGURE reprinted from Mann et al, 2003, Eos,
(C) American Geophysical Union. Comparison of
proxy-based Northern Hemisphere (NH) temperature
reconstructions (Jones et al., 1998 Mann et al.,
1999 Crowley and Lowery, 2000)
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Doesnt climate change naturally?
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Yes!
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So whats the deal with global warming?
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Carbon Cycle Basics
Natural sources
Natural sinks
Human sources
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Carbon Cycle Basics
CO2 sources
atmospheric CO2
CO2 sinks
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Can we wait to see, before taking action?
3 surprises
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Surprise 1 Exponential increase
CO2 sources
atmospheric CO2
CO2 sinks
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2050
500
450
400
2006
350
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Surprise 2 Feedbacks
CO2 sources
Feedbacks in the system amplify the temperature
response
atmospheric CO2
temperature
CO2 sinks
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Surprise 3 Delayed response
CO2 sources
.75oC in pipeline based on CO2 now in the
atmosphere
atmospheric CO2
temperature
CO2 sinks
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Warmer temperatures would be kind of nice,
wouldnt they?
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Figure 9.5 (a) The time evolution of the
globally averaged temperature change relative to
the years (1961 to 1990) of the DDC simulations
(IS92a). G greenhouse gas only (top), GS
greenhouse gas and sulphate aerosols (bottom).
The observed temperature change (Jones, 1994) is
indicated by the black line. (Unit C). (b) The
time evolution of the globally averaged
precipitation change relative to the years (1961
to 1990) of the DDC simulations. GHG greenhouse
gas only (top), GS greenhouse gas and sulphate
aerosols (bottom). (Unit ).
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Mean Seasonal Cycle
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Mean Seasonal Cycle 69W, 15S
Temp
Prec
Frost Freq
Wet Day Freq
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Mean Seasonal Cycle 67W, 22S
Temp
Prec
Frost Freq
Wet Day Freq
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El Niño, Cold Pacific Events
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Summer Rainfall, Lake Increment
Garreaud Aceituno (1999) CRU gridded
Precipitation data (Dec-Feb) Lake level at
Puno (Dec-Feb)
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Altiplano Precipitation Variability
Garreaud Aceituno (2001)
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Precipitation Trends in Andes
Vuille et al (2003) Station Precipitation
data trends Trends by altitude
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Temperature Trends in Andes
Vuille et al (2003) Station, gridded
Temperature data Variability, trends Model
simulated Temperature Variability, trends
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Does RegCM3 add value when downscaling ECHAM4.5
for South America? (Sub-seasonal
statistics) Sara Rauscher (ICTP, Trieste) Anji
Seth (U Connecticut, Storrs) Brant Liebmann
(NOAA/CDC, Boulder) Suzana Camargo Joshua Qian
(IRI, NY)
.
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Daily Precipitation Frequency
N. Amz S. Amz Mon SE NE

Regional model is as good or better that GCM in
all but the N. Amazon region where a substantial
dry bias is evident
Observed NN-RegCM EC-RegCM ECHAM
(Rauscher et al. 2006)
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Monsoon Rainy Season withdrawal Improved in RegCM3
March Monsoon precipitation correlation with SSTa
Monsoon onset And withdrawal dates
(Rauscher et al. 2006)
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Northeast Dry Spells
Regional model improves the dry spell
frequency in Northeast Brazil, especially during
El Niño years.
(Rauscher et al. 2006)
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South American Monsoon Precipitation and Moisture
Flux in the SRES A2 Scenario Maisa Rojas (U
Chile, Santiago) Anji Seth (U Connecticut,
Storrs) Sara Rauscher (ICTP, Trieste)
Acknowledgement IPCC AR4 Modeling Groups and WG
I for coordinating, archiving and making
accessible the model integrations.
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1970-2000 Monthly Precipitation
Monsoon models capture the annual
cycle. Amazon models simulate spurious
semi-annual cycle, and delay/underestimate
observed late summer (JFM) maximum. Southeast
models underestimate summer rains (NDJF), reduce
the amplitude of the annual cycle.
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1970-2000 Monthly Moisture Flux Div.

(Vertically Integrated)
Amazon simulated semi- annual cycle in moisture
flux divergence compared with annual cycle in
reanalysis. Monsoon moisture flux convergence
increases during onset of rains (SON) and
levels off until end of rains (Mar). Models
capture this. Southeast convergence is strong
in summer (DJF) and weaker rest of year. Only 2
of 6 models simulate this.
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(2070-2100)-(1970-2000) Monthly Precipitation
Monsoon Little agreement among models during
rainy season (NDJFM). Drier early rainy season
(SON), wetter late rainy season (JFM)? Amazon
Little agreement among models during onset of
rains (SON). Most models suggest increased
precipitation during middle/late rainy season
(DJFM). Southeast General model agreement
towards increased precipitation, especially in
spring (OND).
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(2070-2100)-(1970-2000) Mon. Moist. Flx. Divg.

(Vertically
Integrated)
Amazon model agreement increased convergence
during middle/end of rainy season
(DJFM). Monsoon Increased divergence in early
rainy season (SON) and some agreement for
increased convergence during the middle/end of
rainy season (JFM). Southeast model agreement
in enhanced moisture flux convergence,
especially in spring (OND).
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Summary South American Monsoon, SRES A2

• Amazon
• Models simulate semi-annual, low amplitude,
  delayed rains.
• There is little model agreement in precipitation
  change during rainy season onset (SON), due to
  delayed onset in simulations?
• 5 of 6 models suggest increased precipitation
  during the
• middle/late rainy season (DJFM) which is primary
  season in models.
• Monsoon
• The annual cycle is well simulated.
• There is little model agreement in precipitation
  change during the rainy season (Dec-Feb).
• Possible shift in the timing of the rainy season
  (?), with drier conditions early and wetter
  conditions later, is consistent with projected
  changes in moisture flux convergence.
• Southeast
• Models underestimate summer precipitation
  (NDJF).
• Models show general agreement towards increased
  precipitation, especially in spring (OND).
• Consistent with observed trend (Liebmann et al,
  JCL, 2004)

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Discussion Wetter spring in Southeast drier
spring in Monsoon? Although the results in the
Monsoon region are more uncertain than those in
the Southeast, there is some suggestion in the
models towards drier early season and wetter late
season in the monsoon region. The projected
increase in precipitation in the Southeast is
supported by model agreement and observed recent
trends (Liebmann et al, JCL 2004). The
difference between Monsoon and Southeast regions
in spring could imply a southward shift in the
SACZ during early season (OND) (see Nogues-Paegle
and Mo, JCL, 1997), and is perhaps related to
strengthening of the Atlantic subtropical high.
We do see a strengthening of the high in the
model runs (not shown), which would have
implications for moisture transport flux
convergence into the Southeast. Moisture flux
convergence changes seen here are consistent with
this hypothesis.