North pacific cool-down: 1940s-1960s

doi:10.4236/ns.2010.28112

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Vol.2, No.8, 911-914 (2010) Natural Science

http://dx.doi.org/10.4236/ns.2010.28112

North pacific cool-down: 1940s-1960s

Kern E. Kenyon

4632 North Lane, Del Mar, USA; [email protected]

Received 14 March 2010; revised 16 May 2010; accepted 25 May 2010.

ABSTRACT

Between the 1940s and the 1960s there was a

significant lowering of the surface temperatures

of the central North Pacific. This cool-down is

discussed on the basis of analyses of a very

large surface temperature data base, covering

most of the North Pacific, which began in 1947

and continued for at least 30 years afterwards. A

surface area more than 20 degrees of latitude by

approximately 70 degrees of longitude, centered

on 40°N, cooled down within about a ten year

period by typically 0.5℃ and by as much as

1.0℃. Previously a permanent surface and near

surface circulation was proposed in which a

shallow very broad warm surface layer flows

northeastward at mid-latitudes on the eastern

side of the North Pacific while colder water re-

turns southward to the east, west and under-

neath the warm surface current. It is suggested

that variations in this hypothesized circulation,

due to natural causes not yet completely un-

derstood, potentially provide a mechanism for

producing a cooling down (or warming up) of a

large region of the central North Pacific at mid-

latitudes in a relatively short period of time (ten

years or less).

Keywords: Climate Change; Cool-Down; North

Pacific; Sea Surface Temperatures

1. INTRODUCTION

“The earth’s average surface temperature has increased

by about 1.2°F in the past century, with most of the in-

crease occurring from about 1920 to 1950, and again

beginning around 1975” [1]. A curious reader will want

to know what happened between 1950 and 1975. One

might infer from this quote that the earth’s average sur-

face temperature also increased from 1950 to 1975, only

at a slower rate. But since 1982 it has been established

that a “confusing” cooling trend occurred from around

1940 to the 1960s as illustrated by the average surface

temperatures of the Northern Hemisphere [2]. More spe-

cifically, though not explained either, is the fact that the

annual mean temperature of the United States as a whole

lowered between about 1953 and 1968 by roughly 0.7℃

[3]. It is shown below, through analyzing an extensive

set of sea surface temperature data, involving millions of

ship injection temperatures [4], that the temperature of

most of the North Pacific Ocean’s surface waters

dropped, in the mean, by around 0.5℃ within a ten year

span between about 1949 and 1959.

From data analyses published earlier [5,Figure 1]

comes the educated guess that a large slice of the North

Pacific was cooling down simultaneously with the US

within about a 30 year period starting in 1947. The fig-

ure shows sea surface temperatures, averaged over a

month and 5 degree latitude/longitude squares, plotted

against longitude, between California and Japan, along

35°N for six consecutive months. For each month and

longitude three means are compared: 10, 20, and 29

years, all beginning with 1947. Over most of the interior

of the ocean the three curves are nested with the 29 year

mean lying on the bottom, the 10 year mean on top and

the 20 year mean in between these two. Temperature

gaps separating the curves are small, in the 0.1℃ range,

but systematic over a large band of longitudes (about 70

degrees), implying a consistent mean cooling from 1947-

1975 (This cool-down was noticed by the author at the

time the figure was made but not mentioned explicitly in

that paper because it was not relevant to the purpose at

hand).

Here an examination of the cool-down is presented

which is expanded from a single latitude line (35°N) to a

band of latitudes (30-50°N) but at the same time more

narrowly focused in time: the most intense period of

cooling is condensed from 30 to 10 years. It is not that

the author is purposefully avoiding the currently popular

subject of global warming; it is only that the data that are

readily available to him happened to coincide with the

cool-down of the North Pacific, which is sandwiched

between two perhaps better known warming periods.

A characteristic of recent books and position papers

K. E. Kenyon / Natural Science 2 (2010) 911-914

912

Figure 1. Temperature difference map for the surface of the mid-latitude central North Pa

cific. Monthly five degree temperatures from the Namias-Scripps data base were averaged

over two separate five year periods: 1947-1951 and 1957-1961, after which the annual

mean was taken over the twelve months for both periods. Then the 57-61 averages were

subtracted from the 47-51 averages for each five degree latitude/longitude square and

contours (℃) of surface temperature difference were drawn on the map. A cool-down

occurred in a large region in the middle of the map. Hatch marks indicate smaller areas

that warmed up between 47-51 and 57-61. Latitude on the vertical axis, longitude on the

horizontal axis.

on global warming and climate change is that they are

long on discussion but short on data presentation. In this

brief journal article an effort is made to have a more

balanced account. Also it appears that nobody has yet

specifically studied the particular North Pacific SST data

base in terms of short period climate variations in the

way I have chosen to look at these observations here.

2. MAIN RESULT

Figure 1 shows the final product of the analysis: a map

of sea surface temperature differences for the central

area and mid-latitude region of the North Pacific. It is

based on the Namias-Scripps sea surface temperatures,

which extend from coast to coast and from 20-55°N. For

a given month and five degree latitude/longitude square

all reported injection temperatures from merchant ships

were combined to get a single number. In my possession

are computer printouts of the temperatures from January

1947 through December 1977. These printouts were

used to make Figure 1 by means of averaging and sub-

tracting. I do not know if the one month five degree

square average data set continued after 1977. If it did,

somebody could easily use these data to study global

warming as reflected in the surface temperatures of the

North Pacific.

Construction of Figure 1 was carried out as follows.

For each five degree latitude/longitude square and month

a straight five year average was computed starting in

1947 and ending in 1951. Then the annual mean was

made by averaging over the twelve months. Exactly the

same procedure was done for the interval 1957-1961. By

subtracting one set of five-year means from the other a

map of sea surface temperature differences was obtained.

What Figure 1 shows is that between the 1947-1951

annual mean and the 1957-1961 annual mean the whole

central mid-latitude region of the North Pacific cooled

down by typically 0.5℃ and by as much as 1.0℃.

Although the cool-down may have started as early as

about 1940, as mentioned above, there is no way I have

to investigate any warming or cooling of the North Pa-

cific before 1947, which is the start of the Namias-

Scripps sea surface temperature data set. However, a

systematic cooling was found to take place over the 29

year period 1947-1977 along 35°N [5]. Here the cooling

period has been narrowed from the upper end of this 30

year period such that the most intense cooling occurred

within the interval 1947-1961. If desired perhaps a fur-

ther narrowing could be investigated in the time domain

by taking running means instead of five year block av-

erages, which was the simplest way to begin the investi-

gation using the given temperature printouts. Also the

map in Figure 1 could be extended southward to 20°N

and northward to 55°N, but then there are occasional

gaps in the temperature record for some five degree

squares and certain seasons which are outside the normal

shipping lanes.

3. PROCEDURE

Figure 1 can be dissected in various ways, but what fol-

lows comes closest to the actual way it was put together

in the first place. One intermediate step between the raw

data and the final result is shown in Figure 2, which ex-

hibits the five year annual mean surface temperatures as a

function of longitude along 40°N: the solid curve is for

1947-1951, the dashed curve is for 1957-1961. If the

dashed curve is subtracted from the solid one in Figure 2,

K. E. Kenyon / Natural Science 2 (2010) 911-914

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Figure 2. Five year annual mean surface

temperatures (℃, vertical axis) as a function

of longitude along 40°N (horizontal axis).

Solid curve is for 1947-1951; dashed curve

is for 1957-1961.

the temperature differences along 40°N in Figure 1 are

reproduced. It can be seen from Figure 2 that the aver-

aged surface temperatures of 1957-1961 were signifi-

cantly lower by about half a degree Centigrade than the

corresponding ones of 1947-1951 over the entire central

portion of the slice of the North Pacific Ocean at 40°N.

A striking feature is revealed in Figure 2, but due to

the subtraction involved Figure 1 contains no hint of it.

In the eastern half of the ocean there is a large-scale lon-

gitudinal maximum in surface temperature. Proceeding

west from California the surface temperature rises to a

maximum at around 1450W and then decreases again.

The maximum occurs in both curves, and it is a real and

permanent feature as documented previously [5]. Along

35°N there is an analogous maximum is surface tem-

perature. It is interesting that the eastern maximum in

Figure 2 has already survived the annual mean plus five

years of averaging. Were the averaging interval to extend

over 10, 20 or even 30 years the maximum would still be

there.

Figure 3 comes one step closer to the raw data in that

it shows five year averages of surface temperature along

40°N but just for the month of January. Again the solid

curve is for 1947-1951 and the dashed one is for

1957-1961. Here a much larger lowering of the tem-

perature by almost 2℃ between the two periods oc-

curred in the central North Pacific. Also prominent in

both the solid and dashed curves of Figure 3 is the lon-

gitudinal maximum temperature in the eastern Pacific.

Finally, two examples of the basic data are given

along 40°N in Figure 4 for January of two particular

years: 1948 and 1958. A cool-down occurred between

these two Januaries, ten years apart, but it is distributed

mainly in the eastern side of the ocean. Very pronounced

is the longitudinal maximum for January of 1948.

4. DISCUSSION

Although the question of the ocean’s role in climate

change has been forcefully raised [6], so far there are no

answers coming back that can explain a significant sur-

face temperature change (0.5℃) over a large area (70

degrees of longitude by more than 20 degrees of latitude)

in a short time (10 years or less), outside of extreme

conditions like the beginnings and endings of the ice

ages, which are presumed to take place relatively

quickly.

Consider the permanent longitudinal maximum in

surface temperature on the eastern side of the ocean at

mid-latitudes, examples of which are illustrated in Fig-

ures 2-4 (and more in depth studies of which were car-

ried out before [5]). What is the most reasonable inter-

Figure 3. Five year mean temperatures

(℃, vertical axis) for January as a func-

tion of longitude along 40°N (horizontal

axis. Solid curve is for 1047-1951;

dashed curve is for 1957-1961.

K. E. Kenyon / Natural Science 2 (2010) 911-914

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Figure 4. Monthly mean tempera-

tures (℃, vertical axis) for January as

a function of longitude along 40°N

(horizontal axis). Solid curve is for

1948; dashed curve is for 1958.

pretation of this real feature? Since the water to the east,

west and underneath the temperature maximum is colder,

and the air temperature above it is colder too (es-

tab-lished from meteorological data taken on individual

cruises), a plausible explanation is that in order to sus-

tain the permanent longitudinal temperature maximum,

warm surface water must continually be brought in to

the area of the maximum from lower latitudes. In other

words, the longitudinal maximum temperature is the

signature of a broad northward flow of warm surface

water. A comprehensive hydrographic section along

35°N [7] strongly suggests that the broad warm current is

also shallow, about 100 m at the most. Consistent with

this idea is the notion that colder water returns south,

crossing mid-latitudes, to the east and west of the longi-

tudinal temperature maximum at the surface and under

the surface maximum at about 100 m below the surface.

Such a broad surface current, hiding in plain sight un-

til recently put forward [8], is potentially capable of

changing the surface temperature of a large region of the

North Pacific by about 1℃. For example, notice the

variability displayed by the longitude and temperature

scales of the temperature maximum in Figures 2-4.

While existing in every month of every year so far stud-

ied along 35 and 40°N, there are month to month

changes within a single year and year to year changes for

a given month. Inquiries as to exactly how such changes

in sea surface temperature are brought about by changes

in the warm current are projects for the future. Also, al-

though the reality of the permanent longitudinal tem-

perature maximum feature itself at mid-latitudes on the

eastern side of the ocean is not in any doubt, there have

been no independent observational checks on the month

to month changes in this feature that are revealed in the

Namias-Scripps surface temperature data set. Nor have

year to year changes of the longitudinal maximum for a

given month been confirmed by separate means.

How quickly could a change in surface temperature of

1.0℃ be expected to occur over broad reaches of the

North Pacific? If the warm current is indeed chiefly re-

sponsible, then one way to estimate a lower bound on

the required time is the distance traveled by the warm

water divided by its mean flow rate, i.e. an advective

time-scale. Earlier analyses gave the flow rate in the ball

park of 10 cm/sec or less [8] and the travel distance is in

the range of 1,000 to 10,000 km, from which a rough

time-scale of 3 years or less is computed.

Finally, one should add that all the conceivable causes

of the North Pacific cool-down are still not known at this

point, nor is it yet possible to definitely link the observed

cool-down to the influences of man. Optimistically, if

the cool-down were better understood, it may follow that

an increase takes place in understanding the warmings

that came before and after the cooling. Natural causes

involving the proposed northward warm current and its

colder southward return flow are suggested here for con-

tributing to the cool-down, but this method could work

equally well for the warmings. On the other hand, if a

good fraction of the warmings is to be blamed on man’s

activities, then the question is: how can the cool-down in

between two warming periods be accounted for in terms

of the interference of man?

REFERENCES

[1] Emanuel, K. (2007) What we know about climate change.

MIT Press, Cambridge, MA.

[2] Weart, S.R. (2003) The discovery of global warming.

Harvard University Press, Boston.

[3] Moran, J.M. and Morgan, M.D. (1994) Meteorology.

Macmillan College Publishing Company, New York.

[4] Namias, J. (1970) Macroscale variations in sea-surface

temperatures in the North Pacific. Journal of Geophysi-

cal Research, 75(3), 565-582.

[5] Kenyon, K.E. (1977) A large-scale longitudinal variation

in surface temperature in the North Pacific. Journal of

Physical Oceanography, 7(2), 258-263.

[6] Murphy, D. (2007) To follow the water. Basic Books,

New York.

[7] Kenyon, K.E. (1983) Sections along 35°N in the Pacific.

Deep-Sea Res., 30(4), 349-369.

[8] Kenyon, K.E. (1981) A shallow northeastward current in

the North Pacific. Journal of Geophysical Research,

86(C7), 6529-6536.