Global and Regional Climate Change Part 2 during the 20 th and 21 st centuries January 18, 2011 ENVIR/SMA/ATMS/ESS585 Amy Snover, ATMS

Are these regional changes due to anthropogenic climate change? At the scale of the western US, partly –“[35-60%] of the climate related trends of river flow, winter air temperature, and snow pack between are human- induced.” Based on two different GCM simulations, and for one of those two different downscaling approaches Barnett et al Human-induced changes in the hydrology of the western United States. Science Express Reports /science

Outline Assessments of global climate change The greenhouse effect Past changes Projected future changes

How much Carbon Dioxide will be released into the atmosphere? A1B A2 (business as usual) B1 (utopia) Estimates depend on population and economic projections, future choices for energy, governance/policy options in development (e.g., regional vs. global governance) A1B A2 B1 CO 2 Emissions CO 2 Concentrations A1FI

Raupach et al 2007, PNAS (updated) Recent emissions have been near the upper end of the most intense (A1FI) fossil fuel scenario established by the IPCC’s 2000 special report on emissions scenarios A1FI now Actual CO 2 emissions From realclimate.org

Karl & Trenberth 2003

The full range (~1.5˚ to 6˚C) of projected temperature increases represents a combination of emissions and model uncertainties +6˚C +1.5˚C We are in the early stages of an era of rapid climate and environmental change

A1B is a typical “business as usual” ( ) scenario: Global mean warming 2.8 o C; Much of land area warms by ~3.5 o C Arctic warms by ~7 o C; get less warming for lower GG concentrations

Projections of Future Changes in Climate Drying in much of the subtropics, more rain in higher latitudes and in the wet tropics, continuing the broad pattern of rainfall changes already observed.

21 st Century PNW Temperature and Precipitation Change Scenarios Projected changes in temperature are large compared to historic variability Changes in annual precipitation are generally small compared to past variations, but some models show large seasonal changes (wetter autumns and winters and drier summers)

21st century PNW climate scenarios relative to past variability

Coasts Global SLR: 7-23” by 2100 Medium estimates of SLR for 2100: +2” for the Olympic Peninsula +11” for the central coast +13” for Puget Sound Higher estimates (up to 4 feet by 2100 in Puget Sound) cannot be ruled out at this time. Rising sea levels will increase the risk of flooding, erosion, and habitat loss along much of Washington’s 2,500 miles of coastline. 3” 6” 30” 50” ” 40” 20” 10” 6” Projected sea level rise (SLR) in Washington’s waters relative to , in inches. Shading roughly indicates likelihood. The 6” and 13” marks are the SLR projections for the Puget Sound region and effectively also for the central and southern WA coast (2050: +5”, 2100: +11”).

Extreme Events *Judgmental estimates of confidence by IPCC: very likely % chance, likely % chance. Source: IPCC SPM 2007

Sources of Uncertainty 1.Future greenhouse gas and aerosol emissions are especially important for the 2nd half of the 21st Century 2.Different climate models respond in different ways to the same forcing - a consequence of imperfect knowledge and modeling of geophysical processes 3.Different downscaling approaches lead to different local/regional outcomes from the same global climate model climate projection

Climate change and natural variations Climate change may be manifest partly as a change in the relative frequency of natural variations (e.g., El Niños vs. La Niñas) Likely changes very uncertain –It currently isn’t clear if ENSO will be stronger, weaker, or unchanged in a warmer future! (see Collins et al 2010, Nature Geosciences)

Climate change and ENSO Trend-ENSO pattern correlation Ratio of ENSO variability La Niña-likeEl Niño-like variability incr. decr. Most climate models project a background trend to El Niño-like conditions in the tropical Pacific Most climate models project a background trend to El Niño-like conditions in the tropical Pacific They also tend to show weaker teleconnections to N. Pacific climate They also tend to show weaker teleconnections to N. Pacific climate climate models do not show systematic changes in ENSO activity climate models do not show systematic changes in ENSO activity IPCC WG1 2007

Projected changes in the amplitude of ENSO variability the “best” climate models for simulating ENSO show no clear change in ENSO variance as a consequence of increased greenhouse forcing - Collins et al 2010, Nat Geosci

The future will not present itself in a simple, predictable way, as natural variations will still be important for climate change in any location Overland and Wang Eos Transactions (2007) Box1 oCoC Degrees C

Downscaling Relates the “Large” to the “Small” ~200 km (~125 mi) resolution ~5 km (~3 mi) resolution

Downscaling and Regional Climate Modeling Global Climate Model Regional Climate Model (WRF) Statistical Downscaling (BCSD) Bias Correction Stat Downscale 6-hourlyMonthly Time Disaggregation Hourly Output Daily Output km km ~7-32 mi 6 km ~3.7 mi Statistical Downscaling Maps the climate change signal from a global model onto the observed patterns Computationally efficient Can tune to observed climate Preserves uncertainty in Global Climate Models Cannot represent fine-scale patterns of climate change Regional Climate Models (“Dynamic Downscaling”) Extend the physical modeling of the climate system to finer spatial scales Computationally demanding Cannot correct bias in global model Adds to uncertainty from Global Climate Models

150-km GCM High resolution is needed for regional studies Washington Oregon Idaho Cascade Range Rocky Mountains Snake Plain Olympics Global Models Typically have km resolution Cannot distinguish Eastern WA from Western WA No Cascades No Land cover differences

150-km GCM High resolution is needed for regional studies Washington Oregon Idaho Cascade Range Rocky Mountains Snake Plain Olympics Global Models Typically have km resolution Cannot distinguish Eastern WA from Western WA No Cascades No Land cover differences Regional Models Typically have km ( resolution 12 km WRF at UW/CIG Can represent major topographic features Can simulate small extreme weather systems Represent land surface effects at local scales 12-km WRF

Why do we want to simulate the regional climate? Process studies  Topographic effects on temperature and precipitation  Extreme weather  Attribution of observed climate change  Land-atmosphere interactions Climate Impacts Applications  Streamflow and flood statistics  Water supply  Ecosystems  Human health  Air Quality

Regional Climate Modeling at CIG  WRF Model (NOAH LSM) 12 to 36 km (~ mi)  ECHAM5 forcing  CCSM3 forcing (A1B and A2 scenarios)  HadRM 25 km (~15 mi)  HadCM3 forcing

Statistical Downscaling CCSM3 Fall Difference between 1990s and 2040s Low spatial detail for climate change signal °C % Temperature Precipitation (%change)

WRF “Dynamic Downscaling” CCSM3 Temperature Precipitation (%change) Fall Difference between 1990s and 2040s High spatial detail for climate change signal %

Land-Atmosphere Interactions Snow Cover ChangeTemperature Change Change in Winter Temperature (degrees C) Change in fraction of days with snow cover Wintertime Change from 1990s to 2050s Salathé et al 2008

Land-Atmosphere Interactions Wintertime Change from 1990s to 2050s Salathé et al 2008 Solar Radiation