1970­2007Trend 2008Anomalies Appraisalof2008ClimateConditions

AttributionofEvolvingNorthAmericanClimateConditionsJudithPerlwitz1,2,MartinHoerling1,JonEischeid1,2,TaiyiXu1,2andArunKumar3

1NOAA/ESRL/PSD,2CIRES/CUand3NOAA/NCEP/NWS

Observations

CMIP (Anthropogenic Forcings)

AMIP (observed (SST/Sea Ice)

Observations

CMIP (Anthropogenic Forcings)

AMIP (observed (SST/Sea Ice)

Q: What caused North Americanwarmingsince1970?

A:Modelsimulationsindicatethatmostof the observed warming was due toanthropogenic forcing. The physicalprocessofcontinentalwarmingwasviatheinNluenceofSSTandseaicechanges.

Q:Whydid thewarmingnot continuein2008?

A: Model simulations indicate that2008coolnesswascausedbyastrongbout of naturally­induced cooling.This resulted from the continentssensitivity to unusually cold SSTs inthetropicalPaciNic.

Q:What was the natural versus anthropogenic impact on 2008 NorthAmericantemperatures?

A: AGCMs forced by estimates of the natural and anthropogeniccomponentsof2008SSTconditions indicatethatthewarmthinducedbythelatterwasoverwhelmedbythecoolnessinducedbythenaturalstate of SSTs. 2008 NA temperatures would have been considerablycoolerintheabsenceofanthropogenicforcing.

Observed SST

CMIP SST

Obs – CMIP SST