A WARMING TREND AT LITTLE AMERICA, ANTARCTICA

By H. WEXLER Chief Scientist, US-IGY Antarctic Program, National Academy of Sciences, Washington, D.C.

URING recent decades large portions of the Arctic and sub-Arctic have D undergone a marked warming (see for example, Ahlmann 1948, 1953). The outstanding example usually cited is Spitsbergen, where, since 1912, the annual temperatures have increased by 11°F (see Fig. 3) and the winter tem- peratures by more than twice that amount. Analysis of all available reliable data to I940 made by Willett (1950) showed that since 1917 the warming trend in the annual temperature averaged over pentads, is largest at latitudes 70" north and 80" north, 2°F and 5°F respectively. At 70" south latitude, Laurie Island, the only station at such a southern latitude available to Willett, showed a slight cooling trend since 1902.

It is of some interest to examine temperature data at and near the present International Geophysical Year station at Little America, Antarctica (78"11'S, 162~10'W) to see if evidence for a trend can be found. This historic site on the Ross Ice Shelf, first known as Framheim, was occupied by Roald Amundsen from April 1911 through January 1912 ; the meteorological observations were analysed by Mohn (1915). The Byrd expeditions of 1928-30 and 1933-35 occupied nearby sites, Little Americas I and I1 (see Fig. I) and the meteoro- logical observations were summarized by Grimminger and Haines (1939) and Grimminger (1941). In 193g-41, the U.S. Antarctic Expedition established a new camp nearby, Little America 111, and Court (1949) summarized the meteorological observations. The site was occupied for a short period in the summer of 1946-47 by the U.S. Navy ' Highjump ' Expedition. In preparation for the US-IGY Antarctic Program, a new camp, Little America V, was established in December 1955, about 30 miles north-east of Little America 111. In Table I, information on station locations, elevations and distances from the Barrier is given.

TABLE I . Station Information

Distance from Elevation Name Year Latitude Longitude Barrier (miles) (ft, m.s.1.)

Framheim .. . . 1911-12 78"38'S 163'37'W 2'5 36 Little America I . . 1929-30 78'34's 163'56'W I 46 Little America I1 . . 1934-35 78"34'S 163O56'W I 46 Little America I11 . . 1940-41 78"30'S 163'50'W 2 =I5 Little America V . . 1955-58 78"11'S 162~10'W 3'5 144

Fig. I . Location of stations, Framheim and Little America I , 11, 111. V

Thus, a t the time of writing, there are six years of observations available at four different sites located less than 35 miles apart near the edge of the ROSS Ice Shelf. Since this great expanse of ice of average thickness 1,300 feet is nearly flat, the temperature observations made at each site can be considered to be representative of a larger area and thus comparable, one with the other. True there might be an effect of distance of the camp from the ' Barrier ' or edge of the shelf. However, only in the brief summer is there open ocean ; in the remainder of the year the frozen ocean extends hundreds of miles to the north. But the prevailing off-shore south-east winds (average speed 13-5 mph) would minimize any ocean effect ; further discussion of this point will be given later in this paper.

It is also possible that the larger size of the present IGY camp and the greater amount of heat given off might exert a positive influence on the present observed temperatures. A comparison of temperatures observed in July 1957 at the primary instrument shelter located IOO feet north of the nearest building and by the ventilated thermohms located 260 feet north-north-east of the nearest building revealed an average difference of only about 0- z°F, with the shelter temperature lower. In November, however, when the temperature

shelter was heated 24 hours daily by the low sun, 'the shelter temperature averaged 1 ~ 3 ° F higher than the themohms ; for light winds (4 mph) the- difference sometimes exceeded 3°F.

As a further check on the influence of the present Little America Camp on- local temperatures, temperatures were measured in November 1958 by H, Neuberg 10 metres deep in the snow 25 metres east of the primary temperature shelter and g metres deep in the snow 2 miles south-south-east of the camp, just beyond Kiel Field. These temperatures, together with earlier temperatures observed by A. P. Crary in 1957 are listed in Table 2.

TABLE 2. Snow temperatures in vicinity of Little America V (LAS)

Date

March 1957 13 Nov. 1958 14 Nov. 1958 Daily 1957 March 1957 June 1957 April 1957

April 1957

- Location

Camp Coldbottom (2 miles NNW from LAS) LAS Camp Site Kiel Field (2 miles SSE from LAS) LAS Camp Site LAS Camp Site LAS Camp Site 20 miles to the south-east of LAS along the

Byrd Trail 40 miles to the south-east of LAS along the

Bvrd Trail

Depth metres

I 0 I 0 9 8 10.5 I5

8

8

Temperature OF

-10.6 -8 .1 -9.9

-9.0 to -10.1

-10.7 -10.1

-12.1

-13.0

Comparison of the LAS Camp Site snow temperature with that at Camp Coldbottom, indicates that in March 1957 the local warming effect on Camp Site temperatures was at least 0 ~ 5 ° F (LAS minus Camp Coldbottom). By Novem- ber 1958 the warming effect had apparently increased close to r-8"F (LAS minus Kiel Field).

The daily mean temperatures at Framheim were computed by taking the average of the 8 a.m. and 8 p.m. local time temperatures (only 3 temperatures daily were taken by sling thermometer). The Little America I and I1 daily average temperatures were found by taking the average of the 24 hourly temperatures while those for Little America I11 were found from the bi-hourly temperatures. The monthly average temperature was computed by taking the algebraic average of the daily averages. For Little America V the monthly average temperature was taken as half the algebraic sum of the average monthly maximum and minimum temperatures. By actual test it was found that the monthly averages computed by the various methods agree to within a few tenths of a degree Fahrenheit.

The annual average temperatures for all stations were found by plotting the monthly averages and equalizing areas above and below the annual average. Observations for Framheim itself are not complete for an entire year, but the missing months of February and March 1911 were filled in by observations aboard the expeditionary ship, Fram, which was tied to the fast ice at Cape Manhue, Bay of Whales, about 2.5 miles west of Framheim.

The average annual temperatures plotted in Fig. 2 have a significant trend of o.103"F per year or 4.7"F from the year 1912 to 1957. Absence of data in the intervening years, of course, makes the linear trend look better than it is.

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1908 I2 16 20 24 28 32 36 40 44 48 52 % 60 " E l R

-10-

-12-

-14-

"C -1s-

-18

-20-

-22-

-24

Fig. 2. Annual average air temperatures observed at Framheim and the several Little Temperatures within the snow at various distances from the ocean are Americas.

indicated by horizontal lines on the ordinate

. t 0 I Y Y C I Y E A R

-

LITTLE AMERICA, 78' 12's. 162'15'W tO 0 5 7 ' C l Y E A R

-

r - * SPITSBERGEN, 78' 0 4 ' N , 13" 38'E

Fig. 3. Temperature trends at Little America and Spitsbergen

It may well have been a coincidence that average temperatures for those years when observations were available fell close to a straight line. For example, if in Fig. 3 an appropriate choice of years had been made for Spitsbergen (e.g. 1914, 1918, 1921, 1932, 1940, 1950) while omitting all other years, these too would have fallen close to a straight line. However, there is other evidence

which points to the reality of the warming trend at Little America. The 1958 average annual temperature of -12-4"F falls almost exactly on the trend line shown in Fig. 2.

A. P. Crary, Scientific Leader at Little America V, in early 1957 observed temperatures deep in the snow at various distances from the Barrier. These values are plotted in the upper left margin of Fig. 2. The temperatures observed at 10 metres in ice hundreds of feet thick are usually considered to be very close to the annual average air temperature, provided there are no sources of heat from below and the annual accumulation is much less than 10 metres. Apart from areas of high snow drift the second of these conditions is fulfilled at Little America V and vicinity where the average annual accumulation is less than 0 .5 metre.

In general, the farther in from the ocean, the lower is the snow temperature. As indicated earlier, an exception is the o.5"F temperature ilzcrease at 10 metres depth from I mile (Camp Coldbottom) to 3 -5 miles from the ocean caused apparently by camp heating ; however, at 15 metres at the Camp Site the temperature is o - I O F lower than at 10 metres at Camp Coldbottom. Thus a mile or two difference in distance from the ocean does not influence the tempera- ture by more than a few tenths of a degree Fahrenheit, an important conclusion if one is to compare temperatures at the various camps located within a strip a few miles wide along the Barrier.

Referring to Table 2, the temperature decreases 2°F in the distance 4 to 24 miles from the Barrier and only o.9"F for the next 20 miles. The decrease of snow temperature away from the ocean shows that there is an effect of oceanic heat on the air temperature, despite the small percentage (less than 20) of the time the winds blow on-shore.

Neglecting for the time being the' possibility of heat transport through the thick shelf ice, we assume that the snow temperatures shown in Fig. 2 are approximately equal to the 1956 average air temperatures. Thus we conclude that the 1956 air temperature is at least 4°F warmer than in 1912 (44-mile snow temperature minus the Framheim air temperature) and may be as high as 6 - 5°F (one-mile snow temperature minus Framheim's). However, these temperature differences are somewhat too large since there is significant heat transport from the warmer ocean below the Shelf Ice as seen by the fact that the 15-metre snow temperature at 4 miles in from the Barrier is 2*7"F higher than the average air temperature for 1956, and nearly I" higher than the 1957 average. Even after correcting for this effect, a comparison of present snow temperatures and the 1912 average air temperature indicates approximately a 4°F warming at Little America since 1912.

For comparison with the Little America warming trend, the average annual temperatures for Spitsbergen (78"04'N, 13'38'E) are plotted in Fig. 3. It is interesting to note first the large temperature difference between a station located at 78" north and a station at 78" south and second, that Spitsbergen displays a significant annual trend of plus 0.250"F or I I O F from 1912 to 1956, more than twice as large as the Little America trend. As shown by the figures

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in Table 3 both trends are significant. data a significant quadratic trend with the maximum near the year 1944.

There is also present in the Spitsbergen

TABLE 3. Correlations with a linear trend line and significance levels

Number Trend Station of years "F/yr Correlation Significance

Spitsbergen 36 0 .250 0.72 0'001

Little America 6 0.103 0.92 slightly less than 0.01

Mchlurdo 7 0'02 0 - 2 3 not significant

The warming in the Spitsbergen-Iceland-Greenland area has often been cited as indicative of a general warming over the Arctic Basin but there are no long station records in the Arctic Pack-Ice, for example, to bear this out. However, there are indications from the thinning out and lateral dissipation of the Arctic Pack-Ice since the turn of the century (Ahlmann 1948) that warming is general over the entire Arctic, although perhaps not so extreme as in the Spitsbergen area.

It would be unwise to claim that the Little America warming trend is typical of the entire Antarctic continent or even the Ross Sea area. The only other comparably long temperature record in Antarctica is found at McMurdo Sound, 400 miles to the west of Little America but here the record is not so reliable. This 40-mile wide Sound is bounded on the east by Ross Island, which is capped by two large mountains, Mt. Erebus, 13,350 feet, and Mt. Terror, 10,755 feet. To the south are several rugged islands and peaks, the highest being Mt. Discovery, 9,090 feet. To the west on the continent itself there rises the magnificent Royal Society Range with peaks rising to 13,350 feet serving as the eastern rampart of the Victoria Land Plateau which rises to heights of 8,000 to 9,000 feet only IOO miles west of Ross Island.

AVERAGE ANNUAL TEMPERATURE AT McMURDO SOUND STATIONS

-17 c . .

Fig. 4. Average annual temperatures a t McMurdo Sound stations

196

Stretched along the west coast of Ross Island for 30 miles are the camps of Scott and Shackleton, bearing such historic names as Hut Point (1902-3), Cape Royds (1908-g), Cape Evans (1911-12). A site close to Hut Point was established as a US. Navy Air Facility in late December 1955, in preparation for the U.S. International Geophysical Year Antarctic Programme. While the distances between these camps and those in the vicinity of Little America are comparable, the meteorology of the McMurdo Sound area is much more complex. In winter f6hn winds flowing down the mountains exert an influence. In summer a mosaic of snow-covered and snow-free portions of Ross Island creates ‘ islands ’ of cold and warm air ; in summer also the open ocean is close by, in some years near Cape Royds, at other times when large areas of the bay ice break away, as far south as Hut Point and even beyond to Cape Armitage

This complex pattern of mountain, bay ice, shelf ice, glaciers, open water, exposed and snow-covered earth makes the combined meteoro- logical record decidedly non-homogeneous. The average annual temperatures for the seven years of record at McMurdo Sound stations are plotted in Fig. 4 ; ‘an insignificant linear trend of plus O - O I I O C per year emerges, which on its face value is less than 20 per cent of the Little America trend. However, no significance is attached to this McMurdo trend as indicated in Table 3.

, (1902 and 1958).

REFERENCES AHLMANN, H. W.: Sow 194s

I953

COURT, ARNOLD I949

GRIMMINGER, G., and HAINES, 1939 w. c.

GRIMMINGER, G. 1941

WILLETT, €1. C. I950

The Present Climatic Fluctuation. Geog. Journ. 112, Nos. 4-6, pp. 165-195 Glacier Variations and Fluctuations. Bowman Memorial Lectures, Sevies 3, Amer. Geog. SOC., N.Y. Meteorological Data for Little America 111. Mo. Wea. Rev. Supple. No. 48 Meteorological Results of the Byrd Antarctic Expeditions 1928-30, 1933-35. Tables. Mo. Wea. Rev. Supple. No. 41 Meteorological Results of the Byrd Antarctic Expeditions 1928-30, 1933-35, Summaries of data. Roald Amundsen’s Antarctic Expedition, Sci. Results: meteorology. Vidensk. Skr. I, math.- nat. Kl., Kristiania, No. 4, pp. 38-72 Temperature Trends of the Past Century, Centenary Proceedings of Roy. Met. SOC., pp.

Mo. Wea. Rev. Supple. No. 42

195-206

ERRATA

of Weather, page 185, line 19, for IOO km, read 10,000 km.

page 175, line 10, for 140’F read 104’F.

In the report of the Symons Memorial Lecture which appeared in the May 1959 issue

In the article ‘ Looking back on 1958 ’ by R. E. Booth, also in the May 1959 issue,