Papers and Proceeding1· of the Royal Society of Tasmania, Volume 122(1 ), 1988 107

AN ANALYSIS OF AIR TEMPERATURE RECORDS FOR MACQUARIE ISLAND: DECADAL WARMING, ENSO COOLING AND SOUTHERN HEMISPHERE CIRCULATION PATTERNS

by D.A. Adamson, P. Whetton and P.M. Selkirk

(with five tcxt-ligurcs)

ADAMSON, D.A., WHETTON, P. & SELKIRK, P.M., 1988 (viii): An analysis of air temperature records for Macquarie Island: decadal warming, ENSO cooling and Southern Hemisphere circulation patterns. Pap. Proc. R. Soc. Tasm., 122(1): 107-112. Papers presented at the Macquarie Island Symposium, Hobart, May 1987. https://doi.org/10.26749/rstpp.122.1.107 ISSN 0080--4703. School of Biological Sciences and Quaternary Research Unit, Macquarie University, Sydney, Australia 2109; and Department of Geography, Monash University, Clayton, Australia 3 168. Macquarie Island lies close to, but on the eastern side of the boundary between the eastern (Pacific) and western (India-Australia) limbs of the Southern Oscillation. Its temperature record matches that of the area east and southeast of New Zealand, rather than Tasmania. Temperature is inlluenced by atmospheric pressures in the Southern Ocean to the east and west, which can result in a warm northeasterly or cold southerly airllow over the island. It is a sensitive indicator of climatic trends because of its location at high latitude in a longitudinal region of frequent ridge formation and blocking in the Southern Hemisphere circulation. Temperature records for Macquarie Island (1949-86) show a l °C warming trend (twice the global average), accelerating in the last 20 years with eight of the ten warmest years occurring in the last decade. The greatest average rate of warming has occurred in late summer and early autumn and the lowest in spring. In severe ENSO years the island cools. The warming is marked, in relation to the annual mean (4.8° C), and the biological effects should be considered. Key Words: atmospheric change, climatic warming, Southern Oscillation (SO), El Nino-Southern Oscillation (ENSO), Macquarie Island.

INTRODUCTION where the westerly circulating SouthernOcean and atmosphere impinge upon the southwestern Pacific The world has warmed by about 0.5° C over Ocean. Van Loon & Shea ( 1987) point out the both land and ocean during this century, the interest of this region because of its possible Southern Hemisphere showing a more regular involvement in the Southern Oscillation (SO). increase than the Northern (Folland et al. 1984, The present paper analyses the marked Jones et al. 1986). High latitudes in the Northern warming that has been recorded on Macquarie Hemisphere show amplified temperature changes Island, at the meteorological station situated 6 m compared to lower latitudes (Kelly et al. 1982, above sea level near the northern end of the island. Raper et al. 1983), in conformity with theoretical The regional meteorological context and links to predictions (Polar Review Group 1980). In the SO are also considered. Sources of data are Jacka Southern Hemisphere, Jacka et al. ( 1984) noted a et al. ( 1984), supplemented by meteorological warming trend which was more pronounced at records held on the island. higher latitudes. North of Macquarie Island, Salinger & Gunn (1975) showed that New Zealand warmed markedly from about 1935 to 1970, a TEMPERATURE TRENDS period when cooling interrupted the longer-term Macquarie Island mean annual surface warming trend in the Northern Hemisphere. temperature shows a marked upward trend of Climatic data are scarce in the Southern about I ° C since annual records commenced in Hemisphere south of about 45° S (Salinger & Gunn 1949 (fig. I). Eight of the ten warmest years have 1975, Jones et al. 1986). Macquarie Island (54° JO'S, occurred during the past decade, whereas none 158° 56'E), one of the few sites suitable for supplying occurred during the first 19 years of the record. such information, has the additional advantage Warming has occurred in all months (fig. 2), with that it lies southeast of the Australian continent, the largest rise in monthly mean (0.042° C per 108 j), A, A damson, P Whelton and p, M, Selkirk

r 1C annurn) occurring in late sun1mer and autumn Ldegree and the srnallcst go per ann urn) spnng. A-RAOUL I (1!U)"C) of the seasonal in rate of warming IS that of the of both the mean ), northern !itnit of antarctic sea ice i and lone (Pinock 1971). eli-CHATHAM I ':'1' I In Island is greatesl \vhen the sea ice is furthest a\vay and the MS-MAATSUYKER i mid-latitude cio:;cst, pre- C-CAMP8ElL IiS.S"C) because of the Increased of warm northern air southward to the island,

I shows temperature trends at stations near the longitude of Island. With the exception of Raoul Island at 19° IS'S, they show a warming trend that becomes more obvious south­ wards. The temperature records for M acquarie and Campbell Islands are similar in their patterns of warmer and cooler with FIG. /- running means Chatham Island somewhat less so, Maatsuyker temperature (meanfor whole Island shows a different pattern. The graphs of stations in the region east and five-year means of annual temperature Zealand and eastern Australia. suggest that the Macquarie Island trends are more linked to the southeast and east of New Zealand than to Tasmania. The affinities of the climate of Macquarie Island are shown by several studies of Southern Hemisphere pressure. Berlage (I correlated monthly surface pressure at stations around the world with that at Djakarta 0.04 • to show the extent of SO, the fluctuation in pressure between an eastern area, centred on the central and eastern south Pacific, and a western \II fI III .... Mlllllll area, centred on the Australian-indonesian-Indian 0.026 Ocean region. In his analysis, the Southern Ocean .. southeast of New Zealand is part of the eastern III fI II> limb, whereas Tasmania and part of the Southern @ Ocean south of Australia he within the western limb of SO, Macquarie Island lies ncar the bound­ ary between these two vast areas of opposite pressure anomalies. Numerous, more recent analy­ ses confirm a boundary in the global cir­ culation in the general region of Macquarie Island, with a tendency for the island to lie just within the eastern limb of SO (Trenberth 1976, van Loon & Madden 1981, Pan & Oort 1983, van Loon & Shea FIG. 2- The rate of temperature increase at 1985,1987, Gordon 1986). Macquarie Island month hy month over 38 years Figure 3 shows the correlation between from 1949 to 1986. The mean ratefor all months is anomalies of monthiy mean sea-level atmospheric shown. pressure throughout the Australian-New Zealand l09

A

--<\ ---- 4. --_

FIG. 3- Correlation map Island detrended monthly mean temperature anomalies and monlh(v mean sea-level atmospheric nr,',','j'irp anomalies in the Australia-New region. The period analysed was 1970-80 (132 months). The shaded area shows correlation at the 1% level, allowingfor reduction in the number ofdata points due The cal stalions shown region and temperature on Island. For this analysis the long-term trend shown on Macquarie Island was removed. map shows clearly the opposite behaviour of the Southern Ocean to the east and to the west of the island, and the affinity of Macquarie island with the east and southeast of New Zealand. The lemperalUrf' map can be interpreted as showing an effect of wind !vIilcquarie Island (!vi l). direction on temperature. When the atmospheric pressure is high to the east of Macquarie Island (positive anomalies) and low to the west (negative New Zealand, cold southern air flows from the anomalies), the wind direction in the Macquarie-­ Island. Campbell region reflects the conditions and is more northeasterly than usual, thereby bringing warmer northern air southwards. formation and blocking over the Tasman Sea- New occurrcd Zealand region (Wright 1974, & Parcel< 1978, Pierrehumbert et (1/. 1984, Trenbe;rth & Mo 1985) may also direct warm northern air southwards to Island. Invasion northern air from New Zealand and AU'itralia is an obvious means of long-distance dispersal for organisms. For example, the probably arrived from New Zealand on associated Zealand directed warm northern air over the with high pressure to the east of the island. island; similar conditions applied to Campbell and Organisms will no doubt continue to arrive on Chatham Islands. A contrary situation applied in Macquarie Island by natural wind By 1970, when record lowest September temperatures contrast, when there is anomalously pressure we,e recorded for Macquarie island (2.2°C, south of Australia and low pressure southeast of to that in and island (4.3° 110 D.A. Adamson. P. Whet/on and P.Jvf. 5,'elkirk

and wes,ern Australia wbere the waves in the Southern Ocean are generated. To the south of tbis Deacon (1984) noted recent retreat of the northern limit of summer sea ice around l'ntarclica. Examination of the data by lacka I for the period 1973 .. B3 a southwards retreat of sea ice in 2° to 4° latitude in the sector of the coast from about 50° E Land) to about 180 0 10 60° W (Rmis contrast, minor retreat occurred south of the Pacific Ocean and none in the sector from the Atlantic Ocean to south of

180" EFFECT OF THE OSCILLATION eMI Consequences of the SO seesaw in atmo­ pressure, sea-surface temperature and extend far beyond the tropics and sub­ of the region extending from India to the Americas. Influences can also be recognised or inferred around the globe at middle and high latitudes in both hemispheres (Ramaswamy & Pareek 1978, Chen 1982, Harnack & Harnack 1985, Raman & Maliekal 1985, Hense 1986, Peng &. Domros 1987, van Loon & Shea 1987, Wolter 1987). Echoes of SO appear in the Macquarie Island temperature record. The two most severe negative excursions of the SO index during this period mCyclone ~ Cyclone occurred in 1972-73 and 1982-83 and corresponded formation decay closeJy with periods when the island was notably (major region) (major region) cold. Another period of severe cold in 1963 matched a period of negative SO index. During periods of negative index, which are called El Nino-Southern FIG. 5 -- Locations of cyclone formation and Oscillation (ENSO) events, high pressure anoma­ decay in the Australia··New Zealand-Southern lies, droughts and weak monsoons occur over the Ocean region. MI-- Macquarie Island. Modified Australian-Indonesian-Indian region, while the from Kep (I 984}. opposite conditions occur over the central and eastern Pacific. As previously noted, Macquarie Island lies near, but to the east of the boundary pressure to the east and pressure to the west of between these two huge regions. pressure Macquarie Island directed cold southern air anomalies to the west of Macquarie Island and northwards over these two islands. However, negative ones to the east (figs 3 & 4) favour cold Chatham Island was warmer than average, being circulation over the island and lead to under Ihe inl1uence of persistent northerly flow. negative anomalies severe The contrast between the Macquarie island ENSO events. New Zealand, (1975) region of the Southern Ocean and similar latitudes noted a switch to persistently cold southwesterly to the west is also shown in 5. Macquarie air flow in the severe ENSO year of 1972. Of Island is ill an area of cyclone decay. Few cyclones course, other parts of the globe behave differently; form there or to the east, but to the west lies one of for example, Northern Hemisphere land between the most intense areas of cyclone formation in the 0° and 25° N warms during ENSO events (Bradley Southern Ocean (Rice 1982, Kep I The area of et al. ! 987). Possibly the marked cooling on intense cyclogenesis lies south of the Indian Ocean Macquarie lsland and the associated pressure Air U!fnperature record,) J 11

anomalies during severe ENSO events arc both fise of 10 C since ! 949 is related to a globally suonger meridional circulation of the mean annual temperature at such times, and the that warming century. Because the nmrked in relation to the annual mean, consequences should be addressed. The warming on Island fits the size and distnbution of global temperature l,rend and sea birds may be affected if aI, ! 984, .! 0 ncs et ai, That earbon-dioxide- ternperature increase continues. induced warming ofille lower involved as a cause is (Karoly, in press) that warming has occurred in the troposphere at 700 mb altitude over We thank Mr Steve Maequarie Island, with cooling in the lower staff from the Bureau of for access to stratosphere at 50 mb Karoly found that a records and for warm hospitality number of other Southern Hemisphere meteoro­ on the island. Permission from the Macquarie logical stations show similar patterns. This vertical Island Committee to work on the island, temperature pattern of warming at lower levels and and logistic support from the Australian Antarctic cooling above is consistent with retention of heat in Division are acknowledged. Financial the troposphere by a carbon dioxide blanket. support was provided by an Australian Research Warming has occurred at subantarctic and Grants Scheme Grant, a Macquarie oceanic islands lying south of the western limb of University Research and a National Research SO, that is south of the Indian Ocean and Fellowship. Diagrams were drafted by G. Rankin of Australia, including Island, Marion and the original was typed S. Island, New Amsterdam (Jackaetal.1984) H umme!stad. and Heard Island (Allison & Keage 1(86). At these oceanic islands, temperature trends extending over a few decades must reflect similar trends in ocean REFERENCES temperature. On Macquarie island, Loewe (! 957) noted a close connection between simultaneous ALLISON, I.F, & KEAGE, P,L., 1986: Recent changes temperatures of the ocean and the air during in the glaciers of Heard Island. Polar Rec., 23: 1951-54. He also noted that sea temperatures in 255-271. 1951-54 were higher than in ! 912-14, and that the ARDENNY, P.E, & KYLE, B.L., 1986: EI Nino and outgoing longwave radiation: Observations from greatest increase was during summer. The month·, Nimbus 7 ERB. Monthly Weather Rev., 14: by-month increase in sea temperature between the 415-433, two periods shows the same pattern as that for air BERLAGE, H.P" 1957: Fluctuations of the general temperature from 1949 86 shown in figure 2. There atmospheric circulation of more than one year, can be little doubt that sea temperatures around their nature and prognostic value, Koninklijk Macquarie Island are also warming. Although Neeler. Mel. Inst. Mededelingen en Verhande· changes in sea-surface temperature and atmo­ fingen., 69: I 152. spheric circulation patterns have undoubtedly BRADLEY, R,S., DIAZ, H.F., KILADlS, G,N. & occurred, their interactions and relative contri.. EISCHEID, J,K., 1987: ENSO signal in con­ tinental temperature and precipitation records butions to the warming trend are not known. Nature, 327: 497 -SOl. Macquarie Island lies at a preferred location CHEN, W,Y" 1982: Fluctuations in Northern Hemi­ for formation of a ridge in the planetary waves of sphere 700 height field associated with the the Southern Hemisphere (van Loon & Jenne 1972, Southern Oscillation, Monthly Wealher Rev~, M 0 1986) and near a longitude of frequent blocking 110: 808 823. and ridge formation (Wright 1974, Ramaswamy &. DEACON, G., 1984: THE Aln:4 RCnC CIRCUM· Pareek 1978, Trenberth & Mo ! 985), as well as at POLAR OCEAN, Cambridge University Press, the junction between western and eastern limbs of Cambridge. SO. This key location in the Southern Hemisphere FOLLAND, C.K, PARKER, I),E, & KATES, F.E., 1984: Worldwide marine temperature fluctua .. atmospheric circulation, as well as its isolation in lions 1856-1981. Nature, 310: 670-673, the high makes the island an indispcnsible GORDON, N~D" 1986: Th{: Southern Oscillation and meteorological station, particularly for upper New Zealand weather. Monthly Weather Rev., atmospheric studies. 114: 371387, J!2 P.

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