This document summarizes a review of over 240 scientific studies from the last few decades examining evidence of historical climate changes. The review found that the 20th century was likely not the warmest of the last 1000 years, and that the Medieval Warm Period from around 1000-1300 AD and the subsequent Little Ice Age were global phenomena, contrary to previous assumptions. These natural climate variations will help improve climate models.

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>Release NO: 03-10
>For Immediate Release
at
are available online
of key climnat~indicators
>NT TEDTR'Photos
>http:/,,fa-wwWharvard.edu/press/pr
NO SOH
>20th CENTURY CLIMATE
led by.
200 climate studies
A review of mr thal Center for Astrophysics has
>~~nrde MA the HradSiho
-- jail century nor h
>Cambridgevadm3th
>researchers at .snIther fteps warmest 00yas
the
20th century Is te
>determined that the o h pas 000 yers The0
the most extreme wete Warm Period of 0 o10
>the century with Medieval
>revewlsoconirmd that the 1300 to 1900 A.D. were worldwide
ice Age of
>A.D.e andsth Lnittle and North American
continents.
>phnoflea otlimited to the Europea4L ihrta nteLtl
temperatures are fic warmth to
>While 20th centurY worlid show the medieval
parts Of the
>Ice Age period, many of the 20th cenj-ury.
>be greater than that
Baliunas, with
Willie Soon and Sallie
>Smtsnanatooers
aIavdsogte (Center for
teSuyo
>co-authors Craig Idso and Sherwood anaai eae Cnteramfor
>Carbon Dioxide and Global Change) , compiled
thuandsexaine
University Of Dlaare) published by tosnso
>climatic Research, than 240 researc papers
>resltsfrom more oern
dec es. Their reports
over the past four indicators, provides
>researchers and bjological climate in different regions
>multitude of gohsical t~hat occurred
>a detiled aclimate changes
eookY av
years.es
over the last 1000
>around the world imte have
ancient c
eerhadvances -in rec 0 nstructing
>"M ytu felt ith wast
Soon sayst 'soudwes
>Occurred over the past two decades,"L studie fromge
niblt the last,
>time to pull together a large SaMPl aiblt andwdcheng erienfct,
for patterns Of expereIecedAe
>5-10 years and look showing that regions
worldwie
>clear patterns did emerge lows Of ther Lttle IceiAge
od and
Medieval Warm Per are generally cooe thndrg
>the highs of the temperatures
century
>and that 20thwarmth."
>the medieval
is neither
tht the 20th century
>Sn anchs 0 lleagues concluded
000tear5n nfhsoriscit theimoste
>the warmest century over about last
the
thepatr ofhsrilcime
>extreme. Their findings
8/14/2003
__99_E S01j~-jj gfOO3_ceq.txt

2. 2 of 3
~~~~~~~~~~~~~~~~~~~Pag
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both
cliite models simulate
tyad edtob tr
help make computercl ead st bTteri
>variatiOns will more accurael:a
nd leves Thsi
>n~traland man-made changes on, local ahd regional
seially
>cniatera foeat timesae ngfg ro svrl
in simulations on
>especially true
>decades to a century.
Wa~rm Periods Verified-
>--HEistorical Cold,
of reasons, not
chnei ~legn for a number -n
>tuyn clmt ofd climateridiators
bewjldering varet opme Fraigo
>the least of which is the
different climatic vapaacee:andec timpe. atFor
and
>all sensitive to distinct scarofspcerd reofd temperte
>slightly overlapping yet yieldyLryrcordss
ring studies can glade ic cr reord cethose
>example, tree while
>and precipitation
trends, decades oacnuy
longer time scales of seeral
>variables over
climate indicators
analyze numerous r c
and colleagues adane sedmor
>Soon, Baliunas daa glciro eoric
data; cultural lake sediments
>includinlg borehole isotopic anaji
rm
tlgieo
, corals
>retreats; geomorphologY; (carboydates) including dust or
cretree or peat celluloses melt
fsis ne ic a
acultonrate,
sedul ments; river sediments;
>cjologic biolgicl fosil; ne ic
fossils and sdi
>ceial counts; lake phenological (recurringsealoo
in;s iteafor
>layers in ice cores; fossils poclle
and paieontlogia ng treedingeite
>relation to climate) treern growth lin
>sediments; luminescent analysis; dens!ty and shfigtreea
late-wood tem.
>ring width or maximum tree stumps in lakes,
mrhsad
,positions Plus clues ain
ries iofa
detectives, we assemble tees and rgoa lmt
>"Like forensic a specific questionl bout local anomalies during
>odrto answer
>oraner isteeeiecefrntb1climatic Sonsasd"h
th pas no1000ieas" can
>particular time perios ve did exist."
showed that suchanmle
>Cumulative evidence significant
9eods confirmed twotl
range of climate Little Ice Agean t
>Th wordwide thousan yas
th
frce Age
>climate periods in the last The climatic notion of a Leittl
Period. peiode-froma80dt
>the Medieval Warm tol9 00 A.D. and a Medieval Warm wides measrd b
>interval from 1300 confirmed and
to be rather well another ascmeasuredb
>1300 A.D. appears 4
from one rgion to 1 o
>de~it soe dffeences
variables like preciptto:~ogtcce
>other climatic and retreats.
>glacier advances anecdotal evidence
> researchers have ossesed alu as
posstesetee, says
n'laniunas
>"For a long time,.rsaceshv olmat exreme renad
these tth
>5 upporting the existence of established colonies in
Vikinlgs several hundred
>"For example, the scond millenniumlthat died out in England, vineyards
>~einnng f te turned colder. And
the clmae
>yearsnlate whe warmupthesow e
hutuave andc
during the medieval fokupteeindicaors.'
utr alwr
>had flourished
objective data to
>accumulation of fhore a warm pneriodai
provided temlerarureviec sihowtiued a zarontervaic
>The different indicators oemperatre which
Tree ring summer high latitudezones
>the Middle Ages. 1100 A.D. in the thrn
da rtabaseof utee
>from 950 A.D. to warm IPeriod." Anothegree
the "Medieval nortdholattude
>corresponds to over 30-70 degrtee h
>growth from 14 different locationd . Many parts oftewrdso
warm periO
4
centflrt
>shoedsimlaiearly greater tha4 that of the 20th
be
>mhoedieal wiiarmht
fsinii
the Air Force Office
>Th std fned by NASA,
8/4/00

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ARCETY
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dpyisD~~
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Director, Astronomy
Science
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at 2)2-358B2150
, call Jane Davis
For appointments
8/14/2003
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