Yes, the sun (was) driving global warming

A new article published by the Washington Post titled No, the sun isn’t driving global warming attempts to discredit Dr. Willie Soon's peer-reviewed, published research papers, some of which have demonstrated solar influences upon climate. The article does not cite nor provide any scientific rebuttal whatsoever to any specific scientific paper written by Dr. Soon, nor to any of the hundreds of other peer-reviewed published papers demonstrating a solar-climate relationship and potential solar amplification mechanisms. 

Instead, the author cites the repeatedly-debunked and simplistic propaganda attempting to dismiss the role of the Sun in climate change promulgated by the warmist Skeptical Science website. 

These falsehoods include the claim that there was no increase in solar activity during the 20th century. This is debunked by the SkS graph in the article itself shown below. The dark blue moving average line in the graph of total solar irradiance (TSI) clearly demonstrates the average TSI of the first half of the 20th century is much less than the entire 2nd half of the 20th century. Given that many papers have found a lagged effect of solar activity changes upon climate, and the large thermal inertia of the oceans, is it entirely reasonable to expect that a sustained high solar output of the latter half of the 20th century would produce a delayed and gradually increasing trend, as was observed. 

This is better demonstrated by calculating the "sunspot integral" of solar activity, which clearly demonstrates a steady rise in accumulated solar output beginning in the 1930's to the end of the 20th century. The correlation of the sunspot integral to global temperature (~.95) is also far superior to that of CO2 and global temperature (~.35). 

The real hockey stick. See also The Sun explains 95% of climate change over the past 400 years; CO2 had no significant influence

The global warming "pause" began almost simultaneously with the current lull in solar activity, while atmospheric CO2 levels continued a steady rise. Even the IPCC, which formerly completely dismissed the role of the Sun in climate change was forced to admit in the latest assessment report that low solar activity is one potential explanation (of at least 66 others) proposed as a cause of the 18+ year "pause" of global warming. It is nonsense to claim that solar activity only significantly affects climate when temperatures are steady to falling, but not while temperatures are rising. 

The Washington Post article below also claims the solar activity of the late 20th century was not exceptional in comparison to the past millennium, a claim which is refuted by multiple proxy reconstructions including:

• New paper shows 20th century solar activity was at highest levels of past 9,400 years
• New paper finds recent Grand Maximum of solar activity was 'rare or even unique event' in 3,000 years
• Paper shows solar activity at end of 20th century was the highest in 1200 years
• New sunspot record shows accumulated solar energy was at "Grand Maximum" at end of 20th century

The article also attempts to dismiss solar effects upon climate by claiming the 0.1% change in solar output over a solar cycle is insufficient to force global temperatures. This simplistic analysis conveniently ignores hundreds of peer-reviewed papers describing potential solar amplification mechanisms, which suggest how tiny changes in solar output may be amplified by many potential mechanisms and secondary effects to produce large-scale changes in climate. 

In sum, the attempts by warmists to dismiss the role of the Sun in climate change are based upon oversimplified and elementary analyses which conveniently ignore hundreds of peer-reviewed papers finding an increase of solar activity over the 20th century to a solar "Grand Maximum" at the end of the 20th century, solar-driven ocean oscillations -which have profound and lagged effects upon climate, and many other solar amplification mechanisms described in the literature, all of which provide plausible mechanisms and explanations for all or most of the global warming of the 20th century, as well as the current 18-year global warming "pause."

Related posts:

The Sun explains 95% of climate change over the past 400 years; CO2 had no significant influence

Climate Modeling: Ocean Oscillations + Solar Activity R²=.96

Analysis: Solar activity & ocean cycles are the 2 primary drivers of climate, not CO2

Analysis shows accumulated solar energy explains 20th century global warming; no significant effect of CO2

The Time-Integral of Solar Activity explains Global Temperatures 1610-2012, not CO2

Natural Climate Change has been Hiding in Plain Sight

New paper confirms the Sun was particularly active during the latter 20th century

Global warming made simple: How natural variability explains 20th century global warming without man-made CO2

Sunspot Integral v. Temperature

The Sun can't possibly explain global warming

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How climate models dismiss the role of the Sun in climate

How climate models dismiss the role of the Sun in climate change [Part 3]

How climate models dismiss the role of the Sun in climate change [Part 4]

No, the sun isn’t driving global warming

By Chris Mooney February 23

Excerpts:

Despite all the attention to who funds him, it is important to note that much of the controversy here is about Soon’s actual scientific views. While Soon has challenged the conclusions of other climate and environmental researchers on subjects ranging from the vulnerability of polar bears to the planet’s climate history, one of his principal arguments has long been that variations in the behavior of the sun, rather than human caused greenhouse gas emissions, are the central factor driving climate change.

Thus the Heartland Institute, a conservative think tank that lists Soon as one of its experts, calls him “a leading authority on the relationship between solar phenomena and global climate.” In a recent Heartland Institute report, Soon and a co-author wrote that “The Sun may have contributed as much as 66% of the observed twentieth century warming, and perhaps more” — going on to suggest that global cooling may lie ahead, due to the “recently quiet Sun and extrapolation of solar cycle patterns into the future.”

This “it’s the sun” claim is an extremely popular argument with climate change doubters — according to the website Skeptical Science, it is the second most popular anti-global warming argument of them all, second only to “climate’s changed before.” So is there any truth to it? After all, regardless of who supports his research, if Soon is actually right on the substance then we may be getting all worked up about global warming for nothing.

Certainly, the argument that the sun — rather than carbon dioxide pollution — is driving global warming cannot be dismissed out of hand. After all, if there is indeed significantly more solar radiation coming in to the Earth, that would definitely raise the planet’s temperature (and vice-versa). The sun is, after all, where we get most of our energy from. Thus, the argument is at least physically plausible.

However, the idea that the sun is currently driving climate change is strongly rejected by the world’s leading authority on climate science, the U.N.’s Intergovernmental Panel on Climate Change, which found in its latest (2013) report that “There is high confidence that changes in total solar irradiance have not contributed to the increase in global mean surface temperature over the period 1986 to 2008, based on direct satellite measurements of total solar irradiance.”

The IPCC “basically says that global warming is not caused by the sun,” says Gerald Meehl, a senior scientist at the National Center for Atmospheric Research. “The strongest evidence for this is the record of satellite measurements of solar output since the late 1970s that show no increasing trend in solar output during a period of rapid global warming.”

Here’s a graphic, courtesy of Skeptical Science, showing overall trends in solar irradiance and temperature:

The sun’s output clearly does vary, as you can see above. For instance, scientists have identified an 11 year sunspot cycle, and found that at the maximum point for sunspots in the cycle, total solar irradiance is indeed somewhat greater than at the minimum. This can have regional effects on the Earth’s climate, says Meehl. “There is evidence for a solar effect in some regions,” he says, “but not a strong global signal over the era of reliable satellite measurements.”

It isn’t only the IPCC that concludes this. “No satellite measurements have indicated that solar output and variability have contributed in a significant way to the increase in global mean temperature in the past 50 years,” concluded a recent workshop report from the National Academy of Sciences. The report noted that while the 11-year sunspot cycle can lead to changes in total solar irradiance of as much as .1 percent, that only translates into a “few hundredths of a degree centigrade” temperature response on the Earth.

“Clearly the sun matters and if it varied a lot then there would be consequences, but it doesn’t,” explains Kevin Trenberth, a prominent climate researcher who is also at the National Center for Atmospheric Research. “The variations are only order 0.1%.”

Of particular significance is the fact that solar irradiance has not shown an increasing trend over the past several decades, while global temperatures clearly have.

A recent scientific review article on climate and the sun similarly notes “the lack of detection of an underlying irradiance trend in the past three decades,” and concludes, in rather strong terms, that:

Claims that the Sun has caused as much as 70% of the recent global warming … presents fundamental puzzles. It requires that the Sun’s brightness increased more in the past century than at any time in the past millennium, including over the past 30 years, contrary to the direct space-based observations. And it requires, as well, that Earth’s climate be insensitive to well-measured increases in greenhouse gases at the same time that it is excessively sensitive to poorly known solar brightness changes. Both scenarios are far less plausible than the simple attribution of most (90%) industrial global warming to anthropogenic effects, rather than to the Sun.

So in sum: It’s not that the sun can’t influence climate. It can, and it does. And climate scientists have accordingly been studying the influence of the sun for many years.

And they have found that, while the sun certainly is not irrelevant, the case for steadily rising carbon dioxide as the principal factor driving the current warming trend just makes a lot more sense.

Willie Soon and some other climate change doubters would surely argue back against this finding — but it’s a strong consensus finding, as shown above. The weight of expert opinion isn’t with these doubters — but the burden of proof most definitely is.

Changing Sun, changing climate

Changing sun, changing climate

by Bob Carter, Willie Soon & William Briggs

March 8, 2013 Quadrant Online

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Scientists have been studying solar influences on the climate for more than 5000 years.Chinese imperial astronomers kept detailed sunspot records, and noticed that more sunspots meant warmer weather. In 1801, celebrated astronomer William Herschel, the first to observe Uranus, noted that when there were fewer spots the price of wheat soared. He surmised that less “light and heat” from the sun resulted in reduced harvests.

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It is therefore perhaps surprising that Professor Richard Muller (University of California, Berkeley) recently claimed that “no component that matches solar activity” could be identified in his newly reconstructed BEST global land temperature record. Instead, Professor Muller said, carbon dioxide controls our changing temperature.

Can it really be true that solar radiation, which supplies Earth with the energy that drives our weather and climate – and which, when it varied in the past, is known to have caused major climate shifts – is no longer the principal influence on climate change?

Consider the charts that accompany this article. In locations as widely separated as US, the Arctic and China, they show a strong and direct relationship between temperature and incoming solar radiation -- the data for the US coming directly from Professor Muller’s own BEST data! That such a tight relationship between temperature and solar radiation holds for many disparate geographical areas indicates that the US result cannot be dismissed as just a local aberration.

A strong sun-climate relationship requires mechanisms to exist whereby our sun can both cool and warm the Earth. One such mechanism is fluctuations in the total amount of incoming solar energy, but measurements suggest that this is not a dominant effect. Another cause, and probably a more substantial one, is modulation of the amount of solar radiation that reaches earth’s surface by changes in total cloud cover.

Recent work by NCAR senior scientists Drs. Harry van Loon and Gerald Meehl has also emphasized a physical relationship between incoming solar radiation and temperature. These scientists argue indirectly that, in testing for this relationship, daytime maximum temperature is the most appropriate criterion to use to characterize the temperature. This measure is available for the US from the BEST data set, and has therefore been used in plotting the accompanying  graph below.

The reason why many previous studies have failed to identify a strong sun-temperature link may be that they have used the daily average temperature to represent the temperature component of the relationship. This can easily introduce erroneous complications related to the part of each day when the sun shines on the other hemisphere and darkness prevails at any particular site being studied.

Nevertheless, recent analyses indicate that even small changes in incoming solar radiation can have a strong effect on Earth’s temperature and climate. In 2005, research by one of us (Soon) demonstrated the existence of a strong correlation between solar radiation and the anomalies in average temperature for the Arctic over the past 130 years (below).

Since then, we have demonstrated that similar correlations exist for all of the regions that surround the Arctic, including the US mainland and China (below).

The reconfirmation now of a strong sun-temperature relation based specifically upon the daytime temperature maxima adds strong and independent scientific weight to the reality of the sun-temperature connection.

The close relationships between the abrupt ups and downs of solar activity and similar changes in temperature that we have identified occur locally in coastal Greenland; regionally in the Arctic Pacific and north Atlantic; and hemispherically for the whole circum-Arctic region. This suggests strongly that changes in solar radiation drive temperature variations on at least a hemispheric scale. 

Close correlations like these simply do not exist for temperature and changing atmospheric CO₂ concentration. In particular, there is no coincidence between the measured steady rise in global atmospheric CO₂ concentration and the often dramatic multi-decadal (and shorter) ups and downs of surface temperature that occur all around the world.

Ongoing research in collaboration with Professor David R. Legates of the University of Delaware, provides a self-consistent explanation for these apparent sun-climate correlations. Our hypothesis involves exchanges of heat and moisture between the equator and the Arctic region.

Direct evidence now exists that changes in solar activity have influenced what is called the “conveyor-belt” circulation of the great Atlantic Ocean currents over the past 240 years. Interestingly, it transpires that solar-driven changes in temperature, and consequential changes in the volume of freshwater released from the Arctic, cause variations in sea surface temperature in the tropical Atlantic 5-20 years later. That this time lag was not taken into account in earlier sun-climate relationship studies is another reason for their comparative lack of success.

The new peer-reviewed scientific results about sun-climate relationships summarized above are of disparate nature and are obtained with independent datasets stem from several different research groups. Considered together, this new research renders implausible the prevailing assumption that changes in solar activity play no (or only an insignificant) role in climate change.

The hallmark of good science is the testing of plausible hypotheses that are then supported or rejected by evidence gathered from either observation or experiment. The evidence from BEST's newly analysed data, and from our own and other published studies, is strongly consistent with the hypothesis that solar factors are the major cause of multidecadal climate change, especially in the northern hemisphere circum-Arctic regions.

Incidentally, but importantly, BEST's own data also clearly invalidate the alternative hypothesis that CO₂ is the most important cause of observed temperature changes across the USA.

In a nutshell, climate is always changing and it is the sun wot does it.

Willie Soon has been researching the relationship of solar radiation and Earth’s climate at the Harvard-Smithsonian Center for Astrophysics for the past 22 years. William M. Briggs is a meteorology-trained statistician and former associate editor of the Monthly Weather Review. Bob Carter is author of the book Climate: the Counter Consensus, and an Emeritus Fellow of the IPA.

New paper finds Indian climate is influenced by solar activity

A paper published today in Advances in Space Research finds "Indian climate appears to be influenced by solar variability" and the "mechanism for the Sun–climate relationship may be related solar polarity also." The authors conclude,

"Comparison of the relationships between the Indian temperature anomalies and solar activity (SSN) provides evidence favouring a mechanism that depends not only on the level of sunspot activity but also on solar polarity."

and in turn show that this may be related to Svensmark's cosmic ray theory of climate [one of many solar amplification mechanisms described in the scientific literature]:

"Reversal in the polarity of the solar polar magnetic field takes place near the solar activity maximum in each solar cycle, and the large-scale interplanetary magnetic field is an extension of the solar polar magnetic field in space (Smith et al., 1978). It is also known that the large-scale structure of the interplanetary magnetic field is of basic importance for the long-term modulation of galactic cosmic rays (Venkatesan and Badruddin, 1990, Kudela et al., 2000 and Badruddin et al., 2007). There are indications that long-term variability in cosmic ray intensity influences the Earth’s climate (Svensmark and Friis-Christensen, 1997, Kirkby, 2007 and Rao, 2011). Thus, we have studied the Sun–climate relationship by averaging the data over the time scales of solar polarity epoch (peak to peak SSN). Averaged over this time scale, we found a significant improvement in correlation between and temperature anomalies as compared to decadal and solar activity cycle timescales."

Advances in Space Research

Volume 54, Issue 8, 15 October 2014, Pages 1698–1703

Study of the influence of solar variability on a regional (Indian) climate: 1901–2007

• O.P.M. Aslam, 
• Badruddin^, 

 Show more

DOI: 10.1016/j.asr.2014.06.019

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Highlights

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Influence of solar variability on the Indian climate has been studied.

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Indian climate appears to be influenced by solar variability.

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Mechanism for Sun–climate relationship may be related solar polarity also.

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Abstract

We use Indian temperature data of more than 100 years to study the influence of solar activity on climate. We study the Sun–climate relationship by averaging solar and climate data at various time scales; decadal, solar activity and solar magnetic cycles. We also consider the minimum and maximum values of sunspot number (SSN) during each solar cycle. This parameter SSN is correlated better with Indian temperature when these data are averaged over solar magnetic polarity epochs (SSN maximum to maximum). Our results indicate that the solar variability may still be contributing to ongoing climate change and suggest for more investigations.

Keywords

• Sun–climate relationship; 
• Global warming; 
• Indian climate; 
• Solar activity

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1. Introduction

The long-term increase in the globally averaged yearly mean temperatures registered in the 20th century has raised the question as to what part, if any, of the observed changes can be attributed to human influence and what part, if any, can be attributed to natural phenomena? A measure of natural phenomenon, the sunspot number (SSN) is a solar activity index with long data record. It is frequently used when studying long-term phenomena like climate change, though it may not be the most appropriate index (Georgieva and Kirov, 2006).

The term global warming is now popularly used to refer the recent reported increase in the mean surface temperature of the Earth; this increase being attributed to increasing human activity, and in particular to the increased contribution of greenhouse gases (Carbon dioxide, Methane and Nitrous oxide) in the atmosphere. However, there is a dissenting view of global warming science too, which is at odds with this view of the cause of global warming (see, Khandekar et al., 2005). The physical mechanism of the greenhouse gases has been understood whereas the mechanism of solar influence on weather and climate requires more detailed study (Stozhkov, 2003 and Gray et al., 2010).

Observations over the last century have shown that the climate at most places on our globe has changed considerably. The extent to which these changes result from human and/or natural forcing is a subject of intense study (e.g., Solanki and Krivova, 2003, Hiremath, 2009, Mufti and Shah, 2011, Rao, 2011 and Ahluwalia, 2012). One reason is that both human influences on the environment (e.g., anthropogenic CO₂ in the atmosphere) and solar activity increased considerably over the last century. This covariance hampers isolation of their separate effects. Moreover, the climatic impacts of several forcing factors are still insufficiently understood.

The solar–climate relationship is currently a matter of a fierce debate. Despite the increasing evidence of its importance, solar–climate variability is likely to remain controversial until a physical mechanism is established. Nevertheless, it is important to identify the primary forcing agents since they provide the fundamental reason why the climate changed. A key issue of climate change is to identify the forcing and their relative contributions.

The Sun can have obvious effect on climate change; its radiation is the main energy source for the outer envelopes of our planet. Nevertheless, there is a long-standing controversy on whether solar variability can significantly generate climate change, and how this might occur. Eddy (1976) initiated the modern study of this topic by pointing out that the Maunder Minimum (1645–1715) in sunspot activity corresponded to the oldest excursion of the Little Ice Age (1450–1850). Subsequent studies related to the solar influence on the Earth’s temperature are quite extensive (see, Eddy, 1976, Reid, 1987, Friis-Christensen and Lassen, 1991,Carslaw et al., 2002, Shaviv and Viezer, 2003, de Jager, 2005, de Jager and Usoskin, 2006, Usoskin and Kovaltsov, 2006, Haigh, 2007, Kirkby, 2007, Gray et al., 2010, Beig, 2011, Singh et al., 2011 and Hady, 2013, and references therein), indicating the importance of the problem and that there are many issues that require further investigations. There are indications from recent and past research (e.g., see Lockwood et al., 2011 and Maghrabi and Al Dajani, 2014; and references therein) that some regional climates will be more susceptible to solar changes.

2. Methodology

In this article, we study the solar influence on climate using a climate (temperature) and a solar activity (sunspot) parameter. We used Indian monthly surface temperature data (all India maximum and minimum) anomalies for the period 1901–2007. All India monthly maximum (Tmax) and minimum (Tmin) surface temperature data sets for the period 1901–2007 are available through Indian Institute of Tropical Metrology’s (IITM’s) data archival (http://www.tropmet.res.in/). This data archival contains data of 107 years (each year have 12 monthly values), generated at IITM using instrumental meteorological records of the India Meteorological Department (IMD). They used climatological normals of monthly mean maximum and minimum temperatures for the period 1951–80 for 388 well-spread stations from the monthly weather records of the India Meteorological Department (IMD, 1999). The procedure adopted for monthly all India maximum and minimum temperature data generation has been explained (see, Kothawale and Rupa Kumar, 2005;ftp://103.251.184.5/pub/data/txtn/README.pdf). We have calculated the anomalies in all India maximum (dTmax) and minimum (dTmin) temperature using this monthly temperature data. We have calculated the mean-yearly temperature by taking average over 12 months (January–December). Average of yearly-mean temperature for the period 1951–80 is taken as reference; we calculated the deviation (anomaly in temperature) in yearly-mean temperature of individual years. Using the anomalies in all India maximum and minimum temperature we also calculated anomalies in average temperature [i.e., dTav = (dTmax + dTmin)/2].

Sunspot number is the solar activity parameter available and well documented on monthly and yearly average basis for continuous long periods of time (http://solarscience.msfc.nasa.gov/). The relationship between the anomalies in Indian temperature and SSN has been studied at various time scales relevant for extracting some physical meaning to the Sun–climate relationship.

3. Results and discussion

Fig. 1 shows the sunspot variations from the beginning of the last century. To start with, we have studied the relationship between the decadal averages of sunspot number () and temperature anomalies (, , and (see, Fig. 2a). We observe that, averaged over decadal time scale, there is some correspondence between the solar and climate parameters. However, this correspondence is poor during the last decade of the 20th century and the beginning years (2001–2007) of this century.

Fig. 1. 

Variation of the annual average sunspot numbers (SSN) from 1901 to 2012.

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Fig. 2. 

Variation of the SSN and temperature anomalies of Indian temperature for (a) ‘decadal average’ for the period 1901–2007, (b) the ‘SSN Peak to peak averages’ for the period 1905–2007.

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A Schwabe (solar activity) cycle period may range from 9 to 17 years, measured from one sunspot minimum to the next sunspot minimum, with an average period of 11 years. The Schwabe cycle is the most prominent periodicity in solar activity. It may be more useful to consider the solar cycle average, instead of decadal average, for the study of the relationship between solar activity and climate. Both the durations and the amplitudes of different solar cycles are quite variable (see Fig. 1). Therefore, we performed an analysis to study the Sun–climate relationship for solar cycle averages. We find that relationship between the solar cycle averaged sunspot number () and temperature anomalies is not much different from that observed on the decadal average scale (see, Table 1). Results of correlation analysis between SSN and temperature anomalies at various time scales are tabulated in Table 1, showing value of correlation coefficients (R) along with p-value and confidence interval for confidence level of 95%. The probability of error that is involved in accepting our observed result is represented by p-value, i.e., smaller the p-value, stronger the validity of the observed result (e.g., a p-value of 0.05 indicate that there is a 5% probability that the relation between parameters found in our study is a chance of occurrence). Confidence interval provides a range of possible R values which is likely to include an unknown population. Confidence interval includes zero means the correlation is not significant at the given level of confidence (95%).

Table 1.

Result of correlation analysis between sunspot number (SSN) and temperature anomalies at various time scales.

Time scale			Correlation coefficient
SSN	Temperature	Total periods	dTmax				dTmin				dTav
			R	p-Value	Confidence interval of R for confidence level of 95%		R	p-Value	Confidence interval of R for confidence level of 95%		R	p-Value	Confidence interval of R for confidence level of 95%
					Lower limit	Upper limit			Lower limit	Upper limit			Lower limit	Upper limit
Decadal average	Same period average	1901–2000	0.61	0.0611	−0.032	0.896	0.63	0.0509	0.001	0.902	0.74	0.0144	0.207	0.934
		1901–2007⁎	0.36	0.2768	−0.306	0.789	0.33	0.3216	−0.336	0.776	0.38	0.2490	−0.285	0.798
Solar cycle average	Same period average	1901–1995	0.49	0.1806	−0.256	0.871	0.53	0.1422	−0.207	0.883	0.75	0.0199	0.171	0.944
		1901–2007⁎	0.30	0.3997	−0.406	0.782	0.29	0.4163	−0.415	0.778	0.35	0.3215	−0.359	0.803
SSN peak to peak average	Same period average	1905–1999	0.79	0.0113	0.265	0.954	0.67	0.0483	0.011	0.923	0.89	0.0013	0.552	0.977
		1905–2007⁎	0.68	0.0305	0.088	0.917	0.56	0.0923	−0.108	0.880	0.69	0.0272	0.107	0.920
Max SSN in solar cycle	Solar cycle average	1901–1995	0.39	0.2994	−0.370	0.837	0.65	0.0581	−0.025	0.918	0.72	0.0287	0.107	0.936
		1901–2007⁎	0.26	0.4163	−0.415	0.778	0.41	0.2393	−0.296	0.826	0.38	0.2787	−0.328	0.815
Minimum SSN at the beginning of the cycle	Solar cycle average	1901–1995	0.90	0.0009	0.586	0.979	−0.03	0.9389	−0.681	0.647	0.80	0.0096	0.290	0.956
		1901–2007⁎	0.73	0.0165	0.186	0.931	0.05	0.8909	−0.598	0.659	0.54	0.1071	−0.136	0.873
Solar magnetic cycle average	Average of same period	1905–1999	0.84	0.1600	−0.163	0.989	0.64	0.0634	−0.042	0.915	0.88	0.1200	−0.010	0.992
		1905–2007⁎	0.68	0.2066	−0.506	0.976	0.53	0.1151	−0.150	0.869	0.47	0.4244	−0.704	0.956

⁎

Including data points of recent period (available up to 2007).

Table options

Reversal in the polarity of the solar polar magnetic field takes place near the solar activity maximum in each solar cycle, and the large-scale interplanetary magnetic field is an extension of the solar polar magnetic field in space (Smith et al., 1978). It is also known that the large-scale structure of the interplanetary magnetic field is of basic importance for the long-term modulation of galactic cosmic rays (Venkatesan and Badruddin, 1990, Kudela et al., 2000 and Badruddin et al., 2007). There are indications that long-term variability in cosmic ray intensity influences the Earth’s climate (Svensmark and Friis-Christensen, 1997, Kirkby, 2007 and Rao, 2011). Thus, we have studied the Sun–climate relationship by averaging the data over the time scales of solar polarity epoch (peak to peak SSN). Averaged over this time scale, we found a significant improvement in correlation between and temperature anomalies as compared to decadal and solar activity cycle timescales (see Table 1 and Fig. 2b).

Georgieva et al. (2012) recently studied the influence of solar poloidal and solar toroidal-related solar activities on the atmospheric circulation. The highest value of sunspots in a solar cycle, SSN_max, is considered as a proxy for the toroidal field strength (de Jager, 2005). Since the amplitudes of solar activity (SSN_max) in different cycles are quite variable, ranging from ∼50 to ∼200 (see Fig. 1). Moreover, the lowest activity (SSN_min) in the beginning of each cycle is also somewhat variable; we also looked at the relationship between SSN_max of each solar cycle and cycle-averages of temperature anomalies, as well as between SSN_min at the beginning of each cycle and cycle averages of temperature anomalies. The correlations in these two cases are, in general, lower than those found when averaged over peak to peak sunspot periods (see Table 1).

It is well known that the number of sunspots increases and then decreases in approximately 11-year intervals. The 11-year sunspot cycle is actually a 22-year cycle in the solar magnetic field, with sunspots showing the same hemispheric magnetic polarity on alternate 11-year cycles; polarity reversal taking place around solar maximum. Therefore, we have looked for the relationship between the SSN and the temperature anomalies averaged over the solar magnetic cycles. In this case the correlation of with temperature anomalies is somewhat lower as compared to that when averaged over only one polarity epoch. Thus, when averaged over each solar polarity epoch (sunspot maximum to maximum), the relationship between the sunspot number and temperature anomaly is found to be the best among all those discussed above.

The question of a definite relation between temperature and the solar activity is still a matter of debate. Our results, however, indicate that some relationship does exist.

Sunspot cycle 23 was unusual (e.g., see Aslam and Badruddin, 2012 and Hady, 2013, and references therein), the current sunspot minimum has been unusually long, and with more than 670 days without sunspots through June 2009. The solar wind is reported to be in a unique low energy state since space measurements began nearly 40 years ago (Fisk and Zhao, 2009 and Livingston and Penn, 2009). Unfortunately, all India temperature data (Tmax, Tmin) is not available to us after 2007; it would be very interesting to look for Sun–climate relationship during cycle 24.

4. Conclusions

Comparison of the relationships between the Indian temperature anomalies and solar activity (SSN) provides evidence favouring a mechanism that depends not only on the level of sunspot activity but also on solar polarity. In spite of the evidences found during the most part of the past century, the latest temperature rise in the 1990’s (especially during solar cycle 23) is difficult to comprehend from most of the discussed results. However, on the solar polarity scale (sunspot maximum to maximum), there are some indications, from the data up to 2007, that a link between solar activity and climate can still be accounted for, and this connection will be watched with curiosity during the current solar cycle 24 and later periods.