Physics & Astronomy International Journal
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Open AccessOn the importance of the natural components inclimate change study: Temperature rise in the studyof climate change
Abstract

Volume 5 Issue 2 - 2021

The theme of this paper is to show that the temperature rising rate by the greenhouse gases
is only 1/5 of what is generally considered. This conclusion is based on identifying twonatural global changes. One of them is a near-linear change after the Little Ice Age (LIA)
and the second is the Pacific (PDO) and Atlantic AMO) decadal oscillations, together called
MDO. After the end of the LIA in about 1850, the rising rate of temperature rise has been
approximately linear with the rate + 0.3°C/100 years, while the MDO has been super9
posed on it with an amplitude of 0.2°C (the range = 0.4ºC) and the period of 40-60 years.
The combined rise of temperature by the two natural components between 1975 and 2000
(which is considered to be due to CO2 by the IPCC) is 0.47°C; it is comparable with theobserved rise of 0.5°C during the same period. Thus, the contribution of the greenhousegases for the same period is estimated to be at most 0.1°C, not 0.5°C.It is estimated thatthe temperature rise from 2000 to 2100 will be 0.9°C± 0.2°C (=‘recovery’ from LIA +greenhouse gases + MDO), namely 0.3°C + 0.4°C ± 0.2°C, namely between 0.7°C and
1.1°C, assuming that the present production rate of the greenhouse gases is maintained.

Syun Ichi Akasofu,1 Hiroshi L Tanaka2

International Arctic Research Center, University of Alaska
Fairbanks, USA2
Center for Computational Science, University of Tsukuba, Japan
1Correspondence: Syun Ichi Akasofu, International Arctic
Research Center, University of Alaska Fairbanks, USA, Tel 907474-6012, Fax 907-474-5662, EmailReceived: August 14, 2021 | Published: August 27, 2021

Keywords: natural components little ice age Pacific decadal oscillation Atlantic decadaloscillation greenhouse gases

Introduction
Climate change recorded by the observed global temperaturechange consists of both natural component and man-made component(greenhouse gases, etc.). Thus, in order to estimate accurately theman-made component, it is necessary to identify and determine thenatural component and subtract it from observed change. This process
is crucial in identifying man-made component and thus in predicting
future temperature by the greenhouse gases. At present, it is assumed
that the observed increase of global temperature is considered tobe mostly by the greenhouse gases without subtracting the naturalcomponent. Figure 1 shows global temperature changes from 1850 to2010. The IPCC attributed the temperature rise during the last part ofthe last century, particularly from about 1975 to 2000, was due “verylikely” to the warming by the greenhouse gases (IPCC 2007).Thisclaim and the rate of increase have become the basis of predicting
future temperatures by a large number of computer simulation studies
since then. In Figure 1, it may be also noted that there was a similarrise from 1910 to 1940, but then a slight decrease until 1975. This has
been no clear explanation for these changes; it is hard to explain themin terms of the increasing trend of the greenhouse gases, because arapid increase of CO2 began in 1946.
Further, the baseline used in Figure 1is chosen to emphasize therapid rise of the temperature after 1975, not the average temperatureduring the period. In this paper, we propose that the rise of temperature
between 1975 and 2000, as well as between 1910 and 1940, is mainly
the combined result of two prominent natural components. The first one
is a near-linear rise after the Little Ice Age (LIA) after 1850 as shownin Figure 2. It is discussed in Section 2. The second one is a semiperiodic natural component superposed on the near-liner component,
which includes both the Pacific Decadal Oscillation (PDO) and theAtlantic Multi-Decadal Oscillation (AMO)1 the combined change iscalled MDO in short; see also Section 3 (p.11).

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Phys Astron Int J. 2021;5(2):73‒76.

The two changes are discussed in Section 2 and Section 3,
respectively. For these reasons, it is worthwhile to review temperaturechanges during the last 400,000 years, since practically all temperaturechanges before 1850 can be considered to be mostly natural change,
although the Industrial Revolution began earlier. Figure 2 shows,from the top, temperature changes from 400,000 years ago (Mullerand MacDonald, 2002). The temperature changes after the four Great
Ice Ages (GIAs)are shown with two extended time scales, the datafrom Greenland GISP 2 Ice Core project and the tree-ring data. TheGISP 2 record shows a gradual decrease of the temperature after thelast GIA. The tree-ring record is clearly recorded in the last part of theGISP2 data (based on the O18 method).
From such an assembly of the past records, it is obvious that there
are always natural changes in progress, so that the natural componentis always present. However, unfortunately, their causes are notknown, except the Milankovitch theory could partially explain theGIAs. Here, it is attempted here to identify two natural components,
which are likely to be persisting at present and also possibly in future.

Temperature change after the Little Ice Age(LIA)
It is reasonably certain that the LIA was present and lasted for about
600 years on the basis of GISP2 and the tree-ring record in Figure 2.
The LIA ended in about1850, and subsequently the temperature has
begun to rise. In a recent paper,2 Gebbie and Huybers showed that thelinear increase began in about 1850. The increase of the temperature
after 1850 was further confirmed by other data sets.3
Tree ring- worldwide
Glacier- (Alaska, Greenland, Alps, New Zealand, Himalaya,Africa, South America),73©2021 Akasofu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which
permits unrestrited use, distribution, and build upon your work non-commercially.

On the importance of the natural components in climate change study: Temperature rise in the study ofclimate change

Copyright:©2021 Akasofu et al.

74

Sea level- including the southern extent and satellite data,
Freezing and breakup – a number of rivers and lakes in the world,
Mg/Ca analysis (Gulf of Mexico),
Cherry blooming (Japan)
The causes of the LIA, the last long cooling period, are notconclusively known. However, there are various ideas on the causesof the LIA, such as changes of solar activities.4 Muscheler showed
their solar modulation function based on cosmic ray changes (deduced
from 14C and 16Be), including the period after the LIA. Figure 3 showstheir result. This function has a similar variation to the temperaturechange deduced from the above tree ring record (Figure 2); on theLIA, see also a recent paper by Hannibal5 Some of the importantcharacteristics of temperature changes during and after the LIA are:I. Both the LIA and the near-linear change after the LIA areworldwide phenomena.
II. Bryant (1997) showed statistically that the rise of temperaturefrom about1850 to 2000 is, as a first approximation, linear with ahigh confidence level; Figure 4.

Figure 3 Solar modulation function based on changes of 10Be and 12C between
1000 and 2000.4

III. The Industrial Revolution began a little before 1800, but thelevel of CO2 at that time was rather small until 1946 (when it
began to increase rapidly), so that it is not possible to attributethe near-liner temperature rise to CO2.
IV. The rate of the near-linear temperature increase from 1850 to2000 is about 0.3°C/100 years, so that it is about 0.07°C/ 25years between 1975 and 2000.
Figure 4 The near linearity of temperature change between 1840 to 2000.16

Since it is reasonable to assume that the LIA is a naturalphenomenon, the near-linear rise between 1850 and 1946 cantentatively be considered to be the ‘recovery’ from the LIA. Further,
there is no specific reason to assume that the near-linear change has
ended in 2000, so that it is reasonable to infer that it continues tothe present and even after 2000.Thus, it is important to subtract theamount 0.3ºC/100 years in estimating effects of the greenhouse effects
in the future.
Figure 1 Temperature variations between 1850 and 2010 (the IPCC). Notethat the chosen baseline is not the average value during the period indicated.

Figure 2 Temperature changes from about 400,000 years ago. The changes
during 400,000 years is shown by shading blue below the baseline and above
in red.13 The second is the Greenland GISP2 Ice Core Project record. The last
one is the tree-ring record.17 Note that GISP2 record reproduces the treering record, red dash line).

Quasi-periodic change: MDO (PDO andAMO)
Superposed on the near-liner rise discussed in Section 2, there aresemi-periodic changes. The MDO are likely to be natural changes,
because the greenhouse gases are not likely to show a periodicchange. Thus, they must be subtracted from the observed temperaturechange in the past in estimate effects of the greenhouse gases. In fact,
as we discuss in the following, it is likely to be the main cause ofthe hiatus. Figure 5 shows the spectral analysis of the changes by
Wu Z.6 Wu Z6 showed that the amplitude associated with the MDO
is roughly 0.2°C and the period is about 40-60 years; note that sinceother semi-periodic changes are also present, these values are onlyapproximate ones. Based on their studies, the contribution of theMDO between 1975 and 2000 is approximately 0.4°C; note that theMDO peaked in 2000, a minimum in about 1950, in the data used byWu Z6 and a maximum in about 2000. The result by Wu Z6 confirmsthat the rise between 1950 and 2000, as well as between 1910 and1940, is a semi-periodic change. Thus, the temperature increase
between 1975 and 2000 was not particularly abnormal, although theCitation: Akasofu SI, Tanaka HL. On the importance of the natural components in climate change study: Temperature rise in the study of climate change. Phys
Astron Int J. 2021;5(2):73‒76. DOI: 10.15406/paij.2021.05.00236

Copyright:©2021 Akasofu et al.

On the importance of the natural components in climate change study: Temperature rise in the study ofclimate change

IPCC claimed the rise is “very likely” due to the greenhouse gases;
particularly because there was a similar increase between 1910 1nd
1940. 7Mantua and Hare mentioned that PDO can be traced back to1600 (tree-rind and coral), the mechanism causing it is not clear, andthe cause of its variability (the periodicity 15-25 and 50-70 years) iscontroversial. The structure of PDO may be characterized by a wedgeshape of warm SST anomaly along the equator over the eastern Pacificassociated with the cold SST anomaly in mid latitudes surrounding
the wedge shape. The anomaly is similar to the La-Nino pattern, but
the timescale is much longer, showing a multi-decadal oscillation.
The PDO index was positive for the period between 1925 and 1945
and also between 1975 and 2000, and negative between 1945 and1975 and also between 2000 and 2014. The index was positive for theperiod between 2014 and 2019 after the strong El-Nino in 2015, but
it returned to negative in 2020.The atmospheric response to PDO is
similar to El-Nino in that the global scale warming (cooling) occurs
for the positive (negative) index.

75

seen that about a half of the rapid warming trend during 1975 to 2000
can be explained by the albedo change (natural variability).

Figure 6 Multi-decadal variability of Northern Hemisphere mean temperature(blue) owing to the albedo change, superimposed on the linear trend expectedby the recovery from the LIA during 1900 to 2020 (red). Arrows after 1958
show radiative forcing by albedo change.8

Figure 5 The spectral analysis of temperature changes between 1860 to2010 by Wu.6 Both the near-linear change and the periodic changes can berecognized.

In contrast, the structure of AMO may be characterized by the mean
SST anomaly over the North Atlantic. The AMO index was positive forthe period between 1930 and 1960, and also between 2000 and 2020,and negative for the period between 1890 and 1930 and also1960 and2000. The timescale of AMO is apparently longer than that of PDO,
showing the period of 60 to 70 years. Both PDO and AMO are thekey factors of climate change of the multi-decadal oscillation (MDO).
Since the MDO plays a very important role in climate change, it isworthwhile to examine its variability. Specifically, it is shown thatthe variability of MDO can be quantitatively explained by changesof planetary albedo.8 Tanaka and Tamura examined the variability ofMDO, using JRA-55 reanalysis data by Japan Meteorological Agency.
They found that the time change of the mean planetary albedo in theNorthern Hemisphere during 1958 to 2012 is in phase with MDO. The
albedo is ranging from the minimum of 0.319 W/m2 to maximum of0.326 W/m2. The range of variation is about 1% of the mean value ofthe planetary albedo. The 1% variation of planetary albedo represents
4 W/m2 of radiative forcing owing to the strong mean solar radiation of
341 W/m2. Further, since the long-term variability of planetary albedo
may be sensitive to the data assimilation method, they repeated thesame analysis using ERA-Interim and found the same multi-decadalvariability. The time change of planetary albedo was also comparedwith the satellite observations by Palle.9 Thus, the result is interestingin that the change in planetary albedo can be one of the possible causesof the multi-decadal variability in global mean temperature, and thus
the variability caused by planetary albedo can also be considered asa proof of natural change. Their result is shown in Figure 6. It can beFigure 7 Global air temperature (UAH, MSU) and the atmospheric CO2(Mauna Loa).10 note that two sharp increases of the temperature in about
1997-1998 and around 2016-2017 are known as the El Nino effect (naturalchange).

Figure 8 A comparison of a number of simulation results and observedchanges.12

Combined resultscomponents

ofthetwonaturalIn spite of various uncertainties in the above analyses, what is
crucial here is that the combined temperature rise by the near-linear

Citation: Akasofu SI, Tanaka HL. On the importance of the natural components in climate change study: Temperature rise in the study of climate change. Phys
Astron Int J. 2021;5(2):73‒76. DOI: 10.15406/paij.2021.05.00236

On the importance of the natural components in climate change study: Temperature rise in the study ofclimate change

trend (0.07°) and the MDO (0.4°C, namely the range [amplitude0.2°Cx 2]) between 1975 and 2000 is comparable with the observed
temperature rise (0.5°C) between the same period. Therefore, within
the accuracy of observations and analysis, it may be stated that thetemperature rise caused by the greenhouse gases is much smaller
compared with the combined rise caused by the two natural changes
between 1975 and 2000, about 0.1°C, instead of 0.5°C. The above
conclusion can be tested with the records in Figure 7, which shows
the recent satellite temperature data up to 2018 (UAH and MSU;
Humlum,10 together with the CO2 data from Mauna Loa. It can beseen that the rate of the observed temperature rise (0.5°C/25 years)
between 1975 and 2000 has not been continued (see the dash line), inspite of the fact that the amount of CO2 is still rising rapidly. The riseof the temperature between 2000 to 2018 is at most 0.1°C as inferredin the previous section. We can show also here that the effects of thegreenhouse gases are only one fifth of the IPCC assumption on thebasis of the observed CO2. Based on Figure 7, it can be estimated thatthe rate of temperature rise by the greenhouse gases between 1975 and2000 is a little more than 0.2°C/ 100 ppm, instead of 1.0°C/ 100 ppm
by assuming that the temperature rise is caused by the greenhousegases. On the other hand, the TRAC model based on Had CRUT4model uses the rate equivalent to 0.5°C/100 ppm.11 Therefore, therate of temperature rise by the greenhouse gases is overestimated in
the past. Figure 8 shows clearly this fact12 many simulation studies
predict, on the average.13 The temperature increase by 0.4°C (many ofthem even much higher than 1.2 °C) between 2000 and 2020, insteadof the observed 0.1°C or so.

Conclusion
Based on reviewing the earlier studies by others and our own results,
it is shown that the natural components, the MDO and the rise after
the LIA,13 contribute significantly to climate global temperature.15,16 If
this trend would continue until 2100, the temperature17 rise from 2000
to 2100 will be at most 0.9°C (= ‘recovery’ from LIA + greenhousegases + MDO), 0.3°C + 0.4°C ± 0.2°, namely between 0.7°C and1.1°, including the effects of the greenhouse gases by assuming thatthe present increasing rate of the greenhouses gases is maintained.
Although the causes of the two natural changes are not known, andthus they cannot be programed in simulation studies, their presence
should not be ignored. At least,18 Their possible effects in the future
should be mentioned in predicting the temperature in 2100, because
both could be present in 2100. The near-halting or the hiatus isexpected from our study in the earlier sections, because the MDO isentering to the declining phase after peaking in 2000. Further, there
was an earlier hiatus between 1940 and 1975 (Figure 2), indicating
also the importance of the MDO.

Acknowledgments
None

Copyright:©2021 Akasofu et al.

76

Conflicts of interest
The author declares there is no conflict of interest.

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Citation: Akasofu SI, Tanaka HL. On the importance of the natural components in climate change study: Temperature rise in the study of climate change. Phys
Astron Int J. 2021;5(2):73‒76. DOI: 10.15406/paij.2021.05.00236