0 - Byrd Polar and Climate Research Center

A1111als ef Glaciology 21 1995
CD In te rn a ti o nal G laciological Socie ty
Recent warming as recorded in the Qinghai-Tibetan
cryosphere
TANDONG YAO ,
Lan:;_lwu fn slitute of G/acioLogJ1and Geoc1)10logJ1, Chinese Acaden1)1 of Sciences, Lanzhou 730000, China
LO NN IE G. THO~lPSON,
B)lrd Pola r Research Cenler, The Ohio Stale Universil)', Columbus, OH 43214, U.S. A .
KEQl N jIAO,
Lanzhou Institute qf G/aciologJ1 and Geoc1J10/ogy, Chinese Arnde111)1 ef Scimces, Lan<./1ou 730000, China
ELLE N MO S LEY-THO~lPS O N,
B)'rd Polar Research Ceuler, The Ohio Stale Universil)1, Columb us, OH 43214, U.S.A .
ZHlHONG Y ANG
Lanzhou Inslitute of Glaciolog)1and Geoc1J10log)1, Chinese Acaden1)1 of Sciences, La11.: lwu 730000, China
Oxygen-i so tope ra ti os (8 11!0 ) m eas ured on ice cores o n th e QinghaiTibe tan Pl a tea u , China , in creased by 1.2- 2.2%0 from the 1960s to th e 1990s.
"M easurem ents o r th e 8 18 0 conte nt o r prec ipit a ti o n a nd the simult a neo us air
tempera tu res need ed to compute th e tern perature in crease corresponcli ng to th e
18
in crease in 8 0 are currentl y m ad e at the D eling ha :M eteorological Statio n , but the
a mount o r d a ta is no t ye t suffi cient to o bta in a relia bl e result .
ABSTRACT.
INTRODUCTION
Th e Qinghai- Tibeta n (QT) Pl a tea u, C hin a , with a n
a \·erage a lti tud e or over 4500 m, is a regio n sugges ted to
be po tenti a ll y sensitive to th e a nti cipated globa l wa rming
o r th e n ex t ce ntur y (H a nse n a nd o th e rs, 1988 ) .
Thompson a nd o th ers ( 1989 ) a nd Thompson ( 1992 )
18
repo rted th at 8 0 Ya lues fro m th e Dund e Ice Cap ha\·e
bee n much less nega ti ve durin g th e last 60 yea rs. Th e
decad es with th e li gh tes t valu es a re th e 1940s, 1950s a nd
198 0s, a nd th e most rece nt 50 yea r average is nea rl y
unpreced ented in th e H oloce ne. Th e onl y co mpa ra b le
18
8 0 va lu es are for th e H oloce ne m aximum , 60008000 BP. Acco rdin g to th ese d ata , it appears t h at
a tmosp heric clim a ti c wa rming is occ urrin g here. This
pa per reports new cryos pheri c obse r\"a ti ons, based o n
rece nt studi es o n th e QT Pl a tea u , w hi c h indi ca te
dra m atic wa rming here.
EVIDENCE FROM ICE CORES
Th e bes t tempera ture prox ies fi·om ice cores a re 8 18 0 a nd
8D, but here onl y 8 18 0 is disc ussed . Since 1991 , th ere has
bee n a concerted effort to d ete rmin e whe th er th e re is a
positi ve correla tio n between th e 8 18 0 or precipita ti on
196
(snow a nd rain ) a nd co ntempo ra neo us air tempera tures.
To i1wes ti ga te this, samples we re co ll ec ted sp atia ll y a nd
tempora ll y. Th e lo nges t record fo r th ese co llec ti o ns a nd
ana lyses is nea r th e Dund e Ice Ca p (Fig. 1), a t th e
D eling h a tvieteorologi cal Statio n . H ere sa mples we re
co ll ec ted from each snow- o r rai nfall event , a nd a ir
temperat ures reco rd ed at the beginning a nd end o r eac h
prec ipita tion eyent. Figure 2 shows th e seasonal flu c tua tion s o r 8 18 0 and air tempera ture [i·o m J 99 J to 199 3 at
th e D eling ha .M eteoro logical Station . Th e mon thl y va lu es
a re a \·erages or all th e sa mpl es coll ected for th at m onth.
8 18 0 was m eas ured with a Finn ega n iVIat-252 with a n
acc uracy of 0.05%0, a nd a ir temperatures are for the
beginnin g or eac h prec ipi ta ti o n even t.
R o ug hl y 80 % or th e a nnu a l precipitation on th e QT
Pl a tea u fa ll s in summ er, a nd thus fewe r samples were
co ll ec ted durin g winte r a nd ma ny more during summe r.
O ccas io na ll y, th ere was a n entire winte r m onth during
whi ch no precipita ti o n fell. Ob\·io usly, for thi s month
there a re no d a ta (Fi g. 2) . Th e res ults (Fig. 2) indi ca te
ve ry good corres ponden ce betwee n th e seaso nal flu ctu ati o ns or 8 18 0 a nd or a ir tempera ture.
18
Fi g ure 3 illustra tes th e rela ti o nship between 8 0 a nd
a ir temperature for a ll th e sa mples coll ec ted from 199 1 to
1993. In 1992, based upon a limited number of sampl es,
Yao a nd Thompson ( 1992 ) suggested th at a linea r
Yao and others: Recent warming in the Qj11ghai- Tibeta11 C1)IOS/J/iere
50' N
Dunde
Ice Cap
Lanzhou
•
Ji{
CHINA
Fig. 1. Locations
120'
100'
BO'E
of ire cores
and
f/ 11 0
1
relation ship existed betwee n 5 HO a nd a ir temp era ture.
Th e add itiona l d a ta prese nted he re confirm th is ea rli er
con clu sion . Us in g a slope of 0.66 (Fi g . 3 ) a ll ows an
18
es timation th a t an increase (o r d ec rease ) of ! %0 in 5 0
co rresponds to a n increase (or d ecrease) of l .5 °C in air
temp t>ra ture. In ot her wo rds, a n increase (or decrease ) or
l °C correspond s to a n increase (or d ecrease ) of0 .66%0 in
5 18 0. Efforts are co ntinuing to estab lish th e nature of th e
relations h ip be tween a nnu a lly ave raged a ir temp era ture
a nd 5 18 0 . H ope f"ull y, seve ral more yea rs of sa mpling will
make this possibl e.
I ce co res we re recovered fr om seve ra l places on th e
QT P latea u (see Fig. I ) to st ud y clim a tic change in th e
last few d ecades. T he Dund e ice co res were recove red
30'
sam/;fi11g 011 the Qj11glwi- Tibetan Plateau.
(i·om th e northern edge of the p latea u, a nd a compre18
hensive st ud y of th e 5 0 records revea led a temperature
increase in th is region (Th ompson and othe rs, 1989; Yao
and others , 1990 ). I ce-co re stud ies have bee n condu cted
at two new sites : G uliya Ice Cap in th e western Kun lun
Mo untain s (Yao and Thompson , 1992 ) and Tanggu la
G lac ier in th e Tanggula i\ll o untains. On Tangg u la
G lac ie r a 14· m co re was reco ve red a nd 5 18 0 was
m eas ured to provid e a reco rd ex tending back to th e
1930s. A sh a llow co re dril led on Guli ya I ce Cap was a lso
18
ana lyzed fo r 5 0; th e di sc uss ion or the tim e se ries from
0
-2
15
-5
4
-6
10
0
0
-<!
0
......
::::l
0-
VO
0
Q)
-1 0
5
-0
'."
-
~
(ii
-12
......
Q)
a.
E
Q)
-14
0
•Temperature
18
o Ii O(°too)
-16
..
0
0
0(5 -1 5
'."
c..o
-20
•
-25
• •
•
f-
-1 8
-5
-2 0
-22
-10
1990
...- -10
1991
1992
1993
1994
1995
-30
••
I
•
•
•• • •
•
• •• ••
Y= 0 .66t -1 3.5
2
R = 0.69
+--..------.--..........---.---...--~---15
-10
-5
0
5
1,0
15
20
Air temperature ( C)
Year
Fig. 2. Seasonal fl11ctualio11s of the 5111 0 of /mcij;itatio11
collected and of concomitant air lemj;era/11res al the
Deli11glw Meleorologirnl Station.
Fig. 3. The relationshijJ between 518 0 and air lem/1eratures for all the sam/1les collected over 3 )1atrs al !he
Delingh a M eleorological Stalio11 .
197
Yao and others: Recent warming in Lile Qjnglzai- T ibetan Cl)'Osphere
that core has been limited to that for th e T a ngg ula core.
Dating of th ese two co res was acco mplished using a
co mbin a ti on of co untin g th e distinct annual dust a nd th e
18
seasonal va ri a tions in 8 0 (Yao a nd others, 1990 ). The
uncertainty in el a ting these cores is estim a ted to be less
th an 5%.
18
T h e a nnu a l averages of 8 0 sin ce 194 0 fr om
Tanggula G lacier (Fig. '~ a ) a nd Gu liya Ice Cap (Fig.
'~b ) sh ow quite simil ar trends eve n though the y are
l 000 km apart. Two important featur es of th ese reco rds
a re th e warmer periods in th e early 1960s an d th e
wa rming sin ce th e la te 1970s. Th ese warm er intervals
a re acce ntu a ted using a 5 yea r mo ving ave r age (Fig. 4a
a nd b; clash ed lin e) . The most impressive feat ure in
both record s is th e recen t warm in g, w hi ch a ppears to
have begun 2yea rs earlier ( 1969 vs 197 1) o n Gu liya .
The warming (inferred from 18 0 enri chm ent ) since th e
la te 1960s on Ta ngg u la is near ly equi valent fo r bo th
sites.
-13
~
0
u
A
-14
Q)
u
..!!!
-15
:::J
Ol
g>
-16
ro
l-
0 -17
o'!
00°
......
-18
"°
1940
-9
-10
1950
1960
1970
1980
1990
--,.~~~~~~~~~~~~~~~~----.
B
EVIDENCE FROM GLACIER FLUCTUATIONS
AND PERMAFROST
Glaciers cover abo ut 60 000 km 2 on th e QT P la tea u.
Th ere are a number of glacier pa rame ters which may
refl ec t cha nges in the glacier's environm ent: cha nges in
glacier ex tent , thi ckn ess , volume and mass balance . H ere
we ex plore th e changes in glacial ex tent as a proxy
indi cato r of ch a nges in the climate. rr th e a mount of
precipita ti on is ass um ed constant, th e retrea t of a glacier
should impl y wa rm er conditi ons whil e an adva n ce should
impl y climati c coo ling . Th e ass umpti on of co nsta nt
acc umu la ti on is rarely a rea lity, an d temperature and
precipitation are intim a tely linked , but we make this
ass umption to simplify the following disc ussion . Most of
th e glaciers studied in this area a re temperat e a nd show
signs of retrea ting . T emperate glaciers , co mp ared to cold
or " pola r" glaciers, a re more se nsiti ve to temp erature
flu ctua tions (Yao, 1987 ) . Thus, ma ny of th e temperate
glaciers in so uth eas tern Tibet a re retrea ting quite rapidl y.
On e typi cal tem perate glacier, Z epu Glacier, has been
st udi ed in d etail. In 1973 th e terminus of th e glacier
surface was covered with a ve ry thin layer of debri s and
there was no vege tatio n on the surface of th e d ebris
(p erso nal co mmuni cation from Li Jijun ) . \!\/hen revisited
in 1989 , th e gla cier was found to be cove red with a very
thick layer of d ebris with vege tation growing on th e
d ebris. This is cl ear evid ence of a strong g lacia l retreat.
O gives (or Forbes ' bands ) a re also co nsid ered useful for
reconst ru cting the past flu ctua ti ons of glacier velocity
(Lliboutry a nd Re yna ud , 198 1) . In 1989, two sets or
ogives were measured to reco nstru ct glacier ve locity
flu ctuations since th e 1970s on a sm all glacier (Small
Zepu G lacier) near Zepu Glacier. Figure 5 shows th e
annu al flu ct uations of velocity r eco nstru cted from these
two se ts of ogives . Although year-to-yea r flu ctuatio ns a re
evid ent , th e g lacier's velocity has slowed over th e las t 1015 yea rs with a major decrease in th e early 1980s, which is
direct evid ence of glaci er retreat.
A sub-p ola r glacier, Ta ngg ul a Gl acier, h as been
studi ed sin ce 1989. Based on our 5 yea rs of observat ions,
1
this glac ier is slowly retreating at a ra te of 4 m yea r . In
ad diti on to th e meas urement of retreat di stance, other
evid ence of retreat is wo rth noting here. NI.an y pu sh
-11
Q)
.....
0
u
-12
Q)
u
ro
-13
::§'
·; -14
0
-15
-
--
-16
0
~
0
0--0
~
"°
150
E
(9
(.)
Q)
110
>
-17.
7 0-+-~~~~~~,--~~~~~--.-~~~~~
1940
1950
1960
1970
1980
1990
1978
1980
1985
Year
Fig. 4. Annual averages and !he 5jiear nmmng mean
(dashed lines) of 1/8 0 measured in !he T anggula (a) cmd
G'ul[J1a ( b) zce cores.
198
Fig. 5. The glacial velocilies reconstructed from lwo se/s of
ogives (a, b) on Small ,(e/Ju Glacier.
Yao and others: Recent warming in the Qjnghai-Tibetan C1JIOS/Jh ere
Table J. T hinning of jJerma/i·osl on the Qjnghai- T ibetan Plateau
Th ickness of fro zen ground
Site
Jin gxia ngu
(north ern Tibet)
114 D aoba n
(ce ntra l Ti bet)
T otal
thinning
1974
1979
1988
1989
m
m
m
m
111
14
12
10
5
15
o·'·
6.5
6.5
Perm a frost di sapp ea red.
moraines , ind icato rs or glacial ad vance, a re now separated from th e ice m argin of T a nggu la G lacier. T he
pu sh mora ines indi ca te that T anggul a ad va nced at so me
tim e in th e past; however , th eir separation fr om the
ma rgin indi ca tes th a t th e glacier is retrea ting no w. Pu sh
moraines th at are se para ting fr om th e ice ma rgin a re now
more common for glac iers on th e QT Pl atea u. Ten yea rs
ea rlier many of th ese glaciers were ad va ncin g in response
to th e short cold period in th e late 1960s a nd earl y 1970s
(R en Binhui , 1988 ). T h e T a ngg ul a push morain es we re
probabl y forme d durin g thi s ad va nce . T he se parati on of
the pu sh moraines from the ice margin reOects th e
wa rming which h as d omin a ted since th e la te 1970s .
Perma frost is also a n indi cator of clim atic cha nge
(H ae berli , 1990 ). In th e 1970s, a number of boreholes
we re drill ed in th e permafrost a long th e road whi ch
crosses the QT Pl a tea u, ma king it possible to monitor the
cha nge in thi ckn ess or th e p ermafrost a nd gro undtempera ture cha nges in th e p erma frost. Th e boreholes
have been monitored sin ce. A recent stud y (\!\I a ng, 199 3)
demonstrated a cl ear decrease in th e thi ckn ess or th e
permafrost (T ab le 1) and an obvious in crease in gro und
tern p er a tu r es a t l 5 m si n ce th e 19 70s (T a bl e 2) .
Temperature in crease was 0.2- 0 .3°C from th e 1960s to
the 1990s . Temperatu re in creases were also fo und in
perm a frost in north eas t C hin a from whi ch Gu Zhongwei
and oth ers ( 1993 ) inferred a n atmosp heri c warming in
the region.
CONCLUSIONS
The data prese nted in th e paper a re from different
so urces , but a ll indi ca te a rece nt warm in g or the
atmos ph ere ove r the QT Platea u. Most of the glaciers
in thi s region ad va nced as a res ult or th e coo lin g in th e
late 1960s and ea rl y 1970s, b ut ap pear to be retrea ti ng
co ntemporaneo usly with the rapid warming since th e la te
1970s.
18
T h e 6 0 record s sugges t a n average enri chm ent
from th e 1970s to th e 1990s of l .2%o in the Tangg ula ice
co r e a nd 2.2%o in th e Gu li ya ice co r e . Th ese
18
enri chm ents in 6 0 a re indi cative of an incr ease in
atmosp h eric temp er a tures. T h e m ag nitud e of th is
tempera ture rise can be es tim a ted from 6 18 0 m eas urem ents of prec ipi ta ti on and simulta n eo us m eas urem ents
of air tempera ture . Sin ce 199 1, these m eas urem ents
have b een performed at the D eling h a M eteorologica l
Sta ti o n (see a b ove ) . This res ults in too few a nnua l
18
averages of 6 0 a nd tempera ture to interp ret a nnual
18
averages of 6 0 in th e ice co res . Nevertheless , a
prelimin ary interpreta tion was mad e, based on th e
relatio nship between mont hly averages of 6 18 0 a nd
18
tempera ture (a 1% in crease in 6 0 co rrespond s to a
temperature in crease of l .5°C ) . In that case, temp erature r ises from th e 1970s to th e 1990s of 1.8° a nd 3 .3°C
are inferred fr om th e Tanggul a a nd th e Gu liya ice co re,
resp ecti ve ly.
T able 2. Ground-tem/Jernture increase al 15 m in the /Jemuifrosl on the Qjnghai- T ibetan Plateau
Ground temperature
Site
F enghu os han
(north ern T ibet)
1962
1963
1967
1975/76
- 3.5
- 3.5
- 3.5
- 3.4
1979
T oled increase
1984 /85
1989
- 3.3
- 3.3
-3.3
0.2
11 4 D ao ba n
(centra l Tibet)
0.2
0. 3
0.3
0.1
124 Daob an
(so u thern Tibet )
0.5
0.6
0 .7
0.2
Blank mea ns no d a ta.
199
Yao and others: Recent warming in the Qjnghai- Tibetan Cl)IOSjJhere
Th e m <w nitud e of th e in crease in gro und temperatu res
in bot h peren ni a ll y and seaso na ll y fr oze n g ro und
indica tes th at ground - tempera ture in crease a t th e [e,·el
of ze ro a nnua l a mplitud e (10- 15 m below surface) is 0.20. 30C from l 962 to 1989.
ACKNOWLEDGEMENTS
This wor k h as been supported b y th e Na tiona l Nat ura l
Science Fo u ndation or C hin a, th e U.S. Na tiona l Science
Found ation 's Office of C lim a te D yna mi cs a nd Di vision of
Pol ar Progr ams (ATl\11 -85 19794, ATl\11 -89 11 6635 , DPP90 1493 1), th e Nation a l G eograph ica l Society (3323-86 ,
4309-90 a nd 4522-9 1) a nd Th e Ohi o Sta te U ni,·ersity.
W e ex tend our a pprecia tion to Dr \\I . Gre uell , Dr. J.
J ouzel, Dr \!\! . H ae berli , a nd J\!Is I\11. D avis fo r th eir
suggestion s fo r revision of th e pape r. T hi s is contribut ion
No. 934 of th e Byrd Pola r R esea rch Center.
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