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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. F.A.Q. How do we know climate is changing? Doesn’t climate change naturally? So what’s the deal with Global Warming? - PowerPoint PPT Presentation
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  • Climate Change: Why Worry? Primer Seminario de Investigacin SANREM CRSP: Adaptacin al Cambio en los Andes. La Paz, 24-28 Abril, 2006Anji Seth, University of Connecticut

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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 BasicsNatural sourcesNatural sinksHuman sources

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  • Carbon Cycle BasicsCO2sourcesCO2sinksatmospheric CO2

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  • Can we wait to see, before taking action?3 surprises

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  • Surprise 1: Exponential increaseCO2sourcesCO2sinksatmospheric CO2

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  • 35040045050020062050

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  • Surprise 2: FeedbacksCO2sourcesCO2sinksatmospheric CO2temperatureFeedbacks in the system amplify the temperature response

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  • Surprise 3: Delayed responseCO2sourcesCO2sinksatmospheric CO2temperature.75oC in pipelinebased on CO2now in the atmosphere

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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, 15SPrecTempWetDayFreqFrostFreq

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  • Mean Seasonal Cycle: 67W, 22SPrecTempWetDayFreqFrostFreq

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  • El Nio, Cold Pacific Events

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  • Summer Rainfall, Lake IncrementGarreaud & Aceituno (1999)

    CRU gridded Precipitation data(Dec-Feb)

    Lake level at Puno(Dec-Feb)

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  • Altiplano Precipitation VariabilityGarreaud & Aceituno (2001)

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  • Precipitation Trends in AndesVuille et al (2003)

    Station Precipitation datatrends

    Trends byaltitude

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  • Temperature Trends in AndesVuille et al (2003)

    Station, gridded Temperature dataVariability, trends

    Model simulatedTemperatureVariability, trends

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  • Does RegCM3 add value when downscalingECHAM4.5 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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  • (Rauscher et al. 2006) Daily Precipitation FrequencyN. Amz S. Amz

    Mon SE

    NEObservedNN-RegCMEC-RegCMECHAMRegional model is as good or better that GCM in all but the N. Amazon region where a substantial dry bias is evident

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  • (Rauscher et al. 2006)Monsoon Rainy Season withdrawalImproved in RegCM3Monsoon onsetAnd withdrawaldatesMarch Monsoon precipitation correlation with SSTa

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  • (Rauscher et al. 2006)Northeast Dry SpellsRegional model improvesthe dry spell frequencyin Northeast Brazil,especially during El Nio years.

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  • South American MonsoonPrecipitation 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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  • 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.1970-2000 Monthly Precipitation

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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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  • Monsoon: Little agreement among models during rainy season (NDJFM). Drier early rainy season (SON), wetter late rainy season (JFM)?

    Amazon: Little agreementamong 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).(2070-2100)-(1970-2000) Monthly Precipitation

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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 themiddle/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 themiddle/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.

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    The RegCM simulates the precipitation frequency as well or better than the GCM in all but the N Amazon region, where the regional model has difficulty transporting enough moisture into the continent.

    N.B.: observed estimate (black) is CMAP ( Xie & Arkin, 1996)See next slide for definitions of Amazon, Monsoon, Southeast regions.

    N.B. observed estimate (black) is from NCEP/NCAR Reanalysis I (Kalnay et al. 1996)

    These results are entirely consistent with the precipitation annual cycle figure (previous slide).N.B.: The projected increase in precipitation in the Southeast is consistent with the observed trend recorded by Liebmann et al. 2004 (JCL).

    n.b. observed estimate (black) is from NCEP/NCAR Reanalysis I ( Kalnay et al. 1996)

    Again, results are consistent with precipitation changes ( as expected)

    Saras notes: Do not abbreviate heading, find some way to fit it in and spell it outDO you need the part about little change in winter in monsoon? So far the focus has been on the rainy seasonAgain, I would put qualifiers in front of season (i.e., rainy season)N.B.: phrases in red denote model agreement in resulting changes. Phrases in blue are speculative!

    N.B.: phrases in red denote model agreement in resulting changes.Speculation: wetter spring in Southeast and possibly drier spring in Monsoon could imply a shift in the SACZ mode. This would be consistent with the changes in moisture convergence s

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