Geoscience Reference
In-Depth Information
is. increasingly. viewed. in. the. climate. community. as. a. threshold. and. goal. to. stay.
below. (see. Schellnhuber. et. al.. 2006. for. the. history),. and. a. growing. number. of.
political.leaders.have.likewise.stated.their.intention.to.avoid.this.outcome..At.the.
high.end,.scenario.A1FI.(not.shown).results.in.even.higher.climate.forcing.by.2100.
than.A2.or.A1B..Global.emissions.of.CO
2
.from.2000.to.2006.exceeded.even.the.
A1FI.scenario.(Raupach.et.al..2007)..Whether.these.exceedingly.high.emissions.
will.continue.into.the.future.is.beyond.our.expertise.to.judge.
s
paTial
p
aTTerns
of
C
hange
The.IPCC.report.(Christensen.et.al..2007).presented.maps.of.mean.changes,.for.the.
2080-2099.average.minus.the.1980-1999.average,.in.the.A1B.scenario.for.21.mod-
els.over.each.continent..These.results.for.North.America.are.shown.in.Figure 1.5..
Annual. mean. warming. is. greatest. in. the. continental. interior,. in. part,. because. of.
greater. wintertime. warming. in. the. coldest. climates. (Figure 1.5,. top. row,. second.
panel),.with.warming.greater.than.7°C.in.the.Arctic.region..Summertime.warming.
in.North.America.is.greatest.in.the.western.states.and.modestly.exceeds.the.warming.
in.the.other.seasons.
Changes. in. precipitation. are. characterized. by. a. north-south. split,. with. Canada.
and.Alaska.getting.wetter.in.all.seasons.and.nearly.all.model.runs,.and.Mexico.and.
Central.America.getting.drier.in.most.seasons.and.most.models..The.western.United.
States.straddles.an.approximately.east-west.nodal.line..In.winter,.a.slight.majority.
of.models.produce.increases.in.the.Northwest.and.decreases.in.the.Southwest..Most.
of.the.models.show.summer.drying.in.most.of.the.West.up.to.and.north.of.the.US-
Canada.border..The.physical.reasons.for.these.changes. in.precipitation.include.(a).
enhanced. water-carrying. capacity. of. warmer. air,. predominant. in. the. North;. (b). a.
poleward.shift. of. the.wintertime. jet.stream. in.many. models. (Yin. 2005);. and. (c). a.
concomitant. poleward. expansion. of. the. downward. branch. of. the. Hadley. circula-
tion,.which.is.responsible.for.the.existence.and.location.of.desert.regions.at.around.
20°-30°.latitude.globally..Patterns.earlier.in.the.twenty-irst.century.(not.shown).are.
generally. similar. but. smaller. in. magnitude,. and. are. projected. to. be. already. under.
way.but.have.not.been.observed.
T
emporal
C
hange
of
W
esTern
m
ean
T
emperaTure
and
p
reCipiTaTion
On. the. PCMDI. website. (esg.llnl.gov),. climate-modeling. centers. from. around. the.
world.provided.simulations.of.twentieth-century.climate.using.observed.solar,.vol-
canic,.and.greenhouse.gas.forcing..In.addition,.for.the.twenty-irst.century,.a.total.
of.112.runs.are.available.with.the.three.scenarios.B1,.A1B,.and.A2.from.the.World.
Climate.Research.Program.(WCRP).Coupled.Model.Intercomparison.Project.phase.
3.(CMIP3).multimodel.dataset..Maurer.et.al..(2007).describe.the.process.of.regrid-
ding.the.CMIP3.data.to.1/8°.×.1/8°.(latitude.×.longitude),.the.Lawrence.Livermore.
National.Lab-Reclamation-Santa.Clara.University.downscaled.climate.projections.
derived.from.the.WCRP.CMIP3.multimodel.dataset,.stored.and.served.at.the.LLNL.
Green. Data. Oasis. (GDO;. http://gdo-dcp.ucllnl.org/downscaled_cmip3_projections/
dcpInterface.html)..A.user.can.specify.an.averaging.domain.and.in.a.few.minutes.
