Geoscience Reference
In-Depth Information
2.0
1.5
1.0
0.5
0.0
-0.5
FIGURE 1.2
(See color insert.)
Linear. trends. in. temperature. (°C/century). from. the.
HadCRU.0.5°.×.0.5°.dataset,.evaluated.over.the.1901-2000.period..The.contour.interval.is.
0.5°C.per.century.
continue.today..In.most.western.states.there.are.at.least.a.few.stations.above.2000.
m,.but.most.are.in.valley.bottoms..In.many.areas.the.data.are.too.sparse.to.draw.a.
conclusion.about.whether.trends.in.temperature.depend.on.elevation.alone.
In.evaluating.temperature.trends.in.the.mountains,.for.example,.the.issue.of.whether.
temperature.trends.depend.on.elevation,.a.critical.question.concerns.the.separate.roles.
of.“advection”.(the.heat.carried.by.the.wind).and.local.surface-energy.balance,.and.
different.studies.have.reached.different.conclusions..Diaz.and.Bradley.(1997).analyzed.
surface-temperature.records.at.116.sites.and.found.that.many.high-elevation.sites.had.
warmed. more. than. lower-elevation. sites. during. the. twentieth. century,. but. questions.
have. been. raised. about. whether. these. indings. represent. true. surface. trends. or. are.
determined. by. the. varying. exposure. to. advection.. Changes. in. free-air. temperature.
(away.from.the.surface,.measured.by.balloon).have.generally.exceeded.surface.tem-
perature.changes.(Karl.et.al..2006),.but.not.all.studies.reach.this.conclusion.(Pepin.and.
Losleben. 2002;. Vuille. and. Bradley. 2000).. Most. studies. found. no. clear. relationship.
