Geoscience Reference
In-Depth Information
SUMMARY
During.the.past.50.years,.the.inluence.of.rising.greenhouse.gas.concentrations.has.
emerged.as.an.important.factor.in.western.temperature..This.has.directly.affected.
snowmelt. and. streamlow. in. broad. areas.. Climate. models. are. in. universal. agree-
ment. that. rising. temperatures. will. continue. for. all. reasonable. assumptions. about.
future.greenhouse.gas.emissions,.but.the.range.of.warming.even.for.a.single.assump-
tion. about. future. emissions. is. quite. broad. (roughly. 2-5°C. during. the. twenty-irst.
century).. Future. changes. in. precipitation. are. even. less. well. constrained,. although.
most.models.agree.on.drier.summers.for.most.of.the.West.
It.is.also.worth.noting.that.the.temperature.increase.in.any.particular.geographic.
setting.will.quite.likely.not.be.a.steady.monotonic.rise,.but.will.show.occasional.pla-
teaus.and.even.decreases.lasting.a.year.to.a.decade.or.more,.arising.from.stochastic.
events. (e.g.,. volcanoes). and. from. the. inherent. internal. variability. that. is. a. funda-
mental.characteristic.of.the.climate.system..Individual.runs.from.the.IPCC.climate.
models.nearly.always.show.such.behavior,.even.those.models.that.have.strong.warm-
ing.over.many.decades..This.facet.of.the.way.in.which.climate.change.unfolds,.day.
by.day.and.year.by.year,.is.usually.overlooked,.largely.because.the.manner.in.which.
model.results.are.summarized.and.presented.(e.g.,.averaging.as.in.Figure 1.6).masks.
what.is.seen.in.individual.realizations.
Both.ecology.and.climate.have.many.important.issues.that.relate.to.spatial.scale,.
most. especially. the. spatial. scale. of. temporal. variability.. Important. work. remains.
to. be. done. to. understand. and. anticipate. the. ine-scale. spatial. structure. of. climate.
change.in.a.topographically.diverse.landscape..There.are.intriguing.hints.that.this.
structure.will.be.more.complex.than.is.commonly.conceived..Related.to.this,.there.
are.likewise.important.implications.for.the.spatial.scales.at.which.we.monitor.cli-
mate.over.the.long.term.
For. ecological. studies,. these. results. are. important. both. in. understanding. past.
change.and.in.framing.the.predictions.of.future.change..The.discussion.here.empha-
sizes. that. the. limited. signal-to-noise. ratio. of. twentieth-century. climate. change. on.
scales. smaller. than. the. entire. West. make. it. dificult. to. conidently. attribute. local.
changes. to. rising. greenhouse. gases.. To. state. this. point. another. way,. researchers.
should. be. very. cautious. about. attributing. observed. biological. changes. to. (implied.
human-induced).climate.change..Other.patterns.of.variability.become.increasingly.
important.as.the.spatial.scale.of.analysis.diminishes.
ACKNOWLEDGMENTS
We.acknowledge.the.modeling.groups,.the.Program.for.Climate.Model.Diagnosis.
and. Intercomparison. (PCMDI). and. the. WCRP's. Working. Group. on. Coupled.
Modeling.(WGCM),.for.their.roles.in.making.available.the.WCRP.CMIP3.mul-
timodel.dataset..Support.of.this.dataset.is.provided.by.the.Ofice.of.Science,.US.
Department.of.Energy..KTR.would.like.to.acknowledge.the.support.of.the.NOAA.
Western. Regional. Climate. Center. and. the. Regional. Integrated. Sciences. and.
Assessments.Program.
