Changes by the decade Understanding climate patterns that vary on the order of decades,
suchsassthesNorthsAtlanticsOscillation, sissnecessarysforspredictingsregionalseffects.sAspositivesNAOs
indexsmeanssasrelativelysstrongshigh-pressurescentersinsthessubtropics,sleadingstoswarm,swetswinterss
forsnorthernsEuropesandscold,sdryswinterssforsnorthernsCanada.sSOUrCE: Jim HUrrEll
North Atlantic Oscillation Index, 1900–2010
3
2
30-year trend
1
Index
- 1
0
- 2
30-year trend
- 3
1910 1920 1930
1940 1950 1960
Year
1970 1980 1990 2000 2010
But other aspects of regional climate
modeling lag far behind. Many regional
models have yet to incorporate basic
land-use information, like details on
urbanization, forest clearing or irrigation, says Jim Hurrell, a climate modeler
at the National Center for Atmospheric
Research in Boulder. And long-term forecasts of how local precipitation might
change are particularly poor — making
it difficult to anticipate droughts.
Regional models are also only as good
as the global approach that they are fit
into. If the global model contains errors,
“that puts major question marks around
the fidelity of your regional simulations,”
Hurrell says. In particular, global modelers have yet to get a good handle on
“decadal variability,” or internal factors
within the climate system that vary on
a time frame of 10, 20 or 30-odd years.
Such factors include the El Niño
Southern Oscillation, a warming pattern that occurs in the tropical Pacific
every few years, and the Pacific Decadal
Oscillation, a similar but longer-term
pattern associated with cooling in the
central North Pacific. Global climate
models don’t include these phenomena
in detail, but will need to if researchers
want to accurately predict climate in a
particular area decades out.
Only over the last couple of years have
scientists gathered enough relevant data,
such as ocean temperatures from a global
array of buoys called ARGO, to be able to
contemplate how to add decadal variabil-
ity into global models. “It’s an extremely
challenging problem,” Hurrell says.
Explore more
s NASA info on aerosols:
http://earthobservatory.nasa.gov/
Features/Aerosols
Uncertainty in the
climatic landscape
Whilesnotsassdiresassthesstatesofs
understandingsonsaerosolssands
regionalsclimate,sothersareassofss
climatessciencesalsoshavessomes
unansweredsquestions.
Carbon cycle feedback
Uncertaintiessremainsins
knowingsexactlyshowscarbons
cyclessthroughsthesocean,satmospheres
andsland.srisingstemperatures,sfors
instance,scansmeltspermafrostsands
sendsmorescarbonsintosthesatmo-
spheres—sbutsatswhatsrate,sscientistss
don’tsquitesknow.
Ice dynamics
thesgreatsicessheetssatops
AntarcticasandsGreenlands
behavesinsunpredictableswayssasstheys
warm,sandsindividualsglacierssadvances
andsretreatsinsunexpectedswayssass
well.sArcticsseasicesissshrinkingsands
thinningsoverall,sbutsitssexactsbehaviors
issassurpriseseverysseason.s
Clouds
Closelysrelatedstosthesproblems
ofsaerosols,scloudssexhibits
variousspoorlysunderstoodsfeedbackss
onsclimate,ssomesofswhichscomputers
modelsscompletelysmiss.sScientistss
agreesthatscloudssareslikelystosincreases
insasgloballyswarmedsworldsbutsdon’ts
knowshowsstrongsasclimateseffectstheys
mightsexert.
Precipitation
Futureschangessinsrainsors
snowfallswillsdependslargelysons
howsmuchsglobalsatmosphericstempera-
turesrisesscomparedswithsoceansands
landstemperatures.sresearcherssares
stillsworkingstosteasesoutsthesdetails.
Oceanic conveyor belt
Circulationspatternsswithins
thesNorthsAtlanticscarryswarms
waterstosthesnorthsandseast,swheresits
cools,ssinkssandsreturnsssouthsinsas
giantsconveyor-likesloop.sSomesmodelss
ofsabruptsclimateschangeshavesgones
sosfarsasstossuggeststhatsthissconveyors
couldsshutsdownsaltogether,saffectings
climatesacrosssEurope.
Land use
Clearingslandsforsagricultures
orsothersreasonssaffectssthes
amountsofscarbonsthesgroundscans
store.sButsthisseffectsisspoorlysunder-
stoodsandsnotsincorporatedsintosmanys
modelssofsfuturesclimate.s
—Alexandra Witze
