Global Warming and Solar Radiation


Without the impact of solar radiation, the temperature on the earth would be about the same as the temperature of space, which is about -454 F. The amount of radiation reaching the earth is about 1,368 watts per square meter. This is a vast amount of energy, which would require the simultaneous output of 1.7 billion of our largest power plants to match. About 70 percent of this solar energy is absorbed and 30 percent is reflected. However, the amount of solar energy reaching the earth is not constant, but varies in several independent cycles of different degrees of magnitude, which may or may not reinforce each other.

These cycles include a 100,000-year cycle, which results from the elliptical orbit of the earth around the sun, a 41,000-year (obliquity) cycle, which results from the tilt of the earth on its axis, a 23,000-year cycle which results from "climatic precession" or changes in direction of the earths axis relative to the sun, and an 11-year sunspot cycle, during which solar radiation increases and then declines. The most recent sunspot radiation cycle peaked in the year 2000, and currently is approaching a minimum. Curiously, NASA and the Russian Observatory both report that total solar radiation now has peaked, and all these cycles may be simultaneously in decline

Each 100,000-year peak in radiation appears to last about 15,000 to 20,000 years, and each has been coincident with massive surges of carbon dioxide and methane (the green house gasses), into the atmosphere, causing de-glaciation of the Polar and  Greenland ice caps. Surges of these greenhouse gasses have always been vastly greater than the amounts currently being generated by burning fossil fuels. For example, the most recent 100,000-year cycle raised sea levels 400 feet in the first 10,000 years, but since then sea levels have risen very little. In the current warming period, sea levels are rising only about 3 millimeters per year, and temperatures over the last 100 years have risen a modest 0.6 of a degree C.

Superimposed on this latest 100,000-year peak have been 6 secondary warming periods, each coincident with additional surges of carbon dioxide and methane, lasting about 200 years and then subsiding. Each of these previous warming periods was warmer than the current warming period, and current temperatures are below the median for the last 3000 years. Most remarkably, civilization first emerged in the Tigris, Euphrates and Nile River Valleys about 3400 B.C. in that period of great warming, and even more remarkably, each of these secondary surges of greenhouse gasses (none of human origin), has also been coincident with the rise of a major civilization.

For instance, 3,000 years ago in the 1000 B.C. warming period, the Babylonian era emerged. Then, 500 years later, the Greek civilization flourished, followed by the Romans 400 years later. A 1,000-year cold period followed through the dark ages, but then in the very warm 1000 A.D. Medieval Period, the ice and snow melted on Greenland; the Danes farmed there for 200 years, until it froze over again. There are no reports of seaports being flooded during this warm period.

About 500 years after the Medieval period, another surge of greenhouse gasses initiated the Renaissance, which was followed by an unexplained "Little Ice Age" from about 1600 to about 1750. (This was coincident with the Maunder Solar Radiation Minimum). During this period, Europe was covered with ice and snow, growing seasons were short, and starvation was common. Farmer unrest may have triggered the French Revolution. The most recent warming period began as solar radiation rapidly increased.

Interestingly, starting about two decades ago (1988), the total increase of greenhouse gasses into the atmosphere has abruptly stopped, in spite of increased burning of fossil fuels.                                                                 

The forcing agent for these many previous warming periods over millions of years could not have been of human origin, and the measured volumes of carbon dioxide and methane which were coincident with each warming period, were vastly greater than those currently being produced by humans.


For millions of years, the earth has been subjected to successive waves of active warming and cooling. These cycles were not of human origin, and often reached temperatures much greater than those of the current period. The most recent warming period started about 300 years ago following an unexplained "little ice age." Mutually supportive data documenting these episodes have accumulated from many sources. They include cores from the Antarctic ice cap, from the Sargasso Sea, from stalagmites, from ocean up-wellings and from the shells of crustaceans trapped in pre-historic rock formations.

For example, the geological record from some 55 million years ago documents a great warming period, which occurred over a "geological instant." Carbon dioxide surged to about 1000 ppmv, and temperatures rose 5 to 7 F. higher than current global temperatures. (1) Methane also increased dramatically in this and other warming periods, with de-glaciation following each warming period. Recently, an analysis of ice cores from the Antarctic ice cap (2) have shown that over the last half million years, there have been sudden and repetitive powerful surges of carbon dioxide into the atmosphere about every 100,000 years, with rapid de-glaciation, followed then by re-glaciation in long cooling periods. We now are at the latest of these peaks, which terminated the last ice age and raised sea levels about 400 feet.

Interestingly, these Antarctic data indicate that the rise in carbon dioxide then leveled off for unexplained reasons. Also, net increases of both carbon dioxide and methane have now ceased since 1988, although the production of human-generated carbon dioxide, methane and nitrous oxide continue to accelerate .

Termination of this last ice age was coincident with a surge in green house gasses, which peaked about 10,000 years ago.  This 15,000-year radiation cycle is now declining.  In fact, we now might be in another ice age except for the fact that about 5,000 years ago, another surge of methane entered the atmosphere, and unexpectedly reversed the cooling

This curious reversal may have counteracted the solar cooling process and initiated a new warming cycle, since archeological records document the period around 3400 B.C. as a great warming period felicitous for agriculture, and one in which civilization emerged in the Tigris, Euphrates and Nile river valleys. (4) Construction of Stonehenge also occurred at this time in England. Since then, there has been a number of additional 200 to 300 year warming periods, followed by sustained cooling periods.

More Recent Data

Cores taken from the sediments in the Sargasso Sea in the Bermuda Triangle (5) have added to the subsequent climate record. Superimposed on the most recent 100,000-year great surge of carbon dioxide into the atmosphere have been six additional surges over the last 3,000 years.

Since the emergence of civilization, and until relatively recently, economic prosperity has been primarily based on agriculture, and each of these warming periods has been accompanied by an improved climate for growing food. After each surge, subsequent declines in green house gasses resulted in significant cooling of the climate and shorter growing seasons, perhaps contributing also to observed societal declines.

For example, three thousand years ago (1000 B.C.), the Babylonian civilization emerged and then flourished until the climate cooled. A second great surge in carbon dioxide, also of non-human origin, occurred about 500 B.C. coincident with the emergence and subsequent flourishing of the Greek civilization. The Roman civilization emerged during the next surge in carbon dioxide, after which there was an extended cooling period that encompassed the Dark Ages.

Then, in 1000 A.D., a fourth surge of carbon dioxide accompanied the Medieval Warming Period, during which much of the ice and snow on Greenland melted; for the following 200 years the Danes farmed Greenland. Presumably, much of the Antarctic snow and ice must also have simultaneously melted, but there are no records of massive flooding of coastal cities. This period also saw the collapse of the Mayan civilization as a serious drought covered Mexico and the U.S. Midwest. Massive sand dunes were formed in Nebraska during this period, and the Easter Island culture in the Pacific Ocean also collapsed at this time. A cooling period followed until the surge in 1500 A.D. which was coincident with the Renaissance and then the beginning of the Industrial Revolution, but also saw the collapse of the Angkor civilization in Cambodia, when the canals from the Siem Reap River dried up and the rice economy was devastated. (6)

The 1500 A.D. warming period ended, curiously, in a "little ice age" when much of Europe was covered with ice and snow. This was followed by the start of the current warming period about 300 years ago, which also has been accompanied by a remarkable increase in methane, a much more potent greenhouse gas than carbon dioxide. Methane, when initially generated, is about 56 to 62 times more potent than carbon dioxide as a greenhouse gas. (7) However, it oxidizes to carbon dioxide over about a 12 year period, and consequently, over a 100 year period, its average effect is thought to be about 21 times that of carbon dioxide.

The amount of methane entering the atmosphere has doubled over the last 200 years and has been rising exponentially until very recently. For unexplained reasons the net rise of both carbon dioxide and methane has ceased since 1988 (Figure V).

Until the recent industrial period, relatively few people inhabited the western world, so these climate changes were not of human origin. (Figure VI).

Greenhouse Gas Sources 

The earth's atmosphere is made up of a number of gasses which are essentially permanent in concentration and others which vary from time to time:    
Figure VII



            Nitrogen               78.9%                          Water                       0 to 4%         

            Oxygen                20.9%                          Carbon Dioxide       0.035%

            Argon                     0.9%                          Methane                   0.0002%

            Neon                    0.002%                        Ozone                     0.000004%

            Helium                  0.005%

            Krypton               0.0001%

            Hydrogen          0.000004%

Water Vapor

Water vapor is a greenhouse gas whose concentrations in computer models are currently not taken into account. Concentrations vary widely, both daily and over different sections of the earth.  Low thick clouds primarily reflect solar radiation, and cool the surface of the earth  High thin clouds primarily transmit incoming solar radiation, but also trap some of the outgoing infrared radiation emitted by the earth, and radiate it back down to the earth, warming the surface of the earth.  The balance between cooling and warming is close, but cooling predominates.

During the last ice age, water vapor over the Antarctic was less than half of current concentrations, and the St Lawrence River at that time had cut a channel to the continental shelf which is now 400 feet below current ocean levels. De-glaciation raised these sea levels and atmospheric moisture also increased. (8) Warming effects due to water vapor seem to be disputed. 

Carbon Dioxide

The amounts of carbon dioxide entering the atmosphere have increased about 1.8% per year since pre-industrial times, rising from about 280 ppmv to 383 ppmv now -- the highest in 160,000 years. However, pre-industrial temperatures were much higher than current temperatures, when carbon dioxide concentrations were at the much lower 280 ppmv.

Massive amounts of this gas are absorbed in the oceans, in terrestrial systems and in the atmosphere, with a relatively labile equilibrium between them. Concentrations in the oceans are about 60 times greater than in the land and atmosphere, and about 20 times greater than in the atmosphere. Any warming of the oceans could release significant quantities of this gas. 

Until the last century, none of these rises in warming could be attributed to human origin. Also, the rate of increased carbon dioxide which accompanied the end of the last ice could not alone have accounted for the abruptness of a 16 F. rise in temperature. Shorter term rapid fluctuations in temperature also were observed in the Sargasso Sea cores. These are inconsistent with more steady increases in Carbon dioxide, but possibly may be due to the onset of sudden warm currents in the Atlantic Ocean. (9) Deforestation and burning of fossil fuels in recent years have added to normal sources of carbon dioxide entering the atmosphere, but net increases now have inexplicably ceased over the last two decades.


Methane is more abundant in the atmosphere now than in the last 400,000 years, when concentrations were 278 ppbv (10). Since the little ice age, concentrations have increased from 700 to 1767 ppbv, but over the last two decades since 1998, they also have ceased to rise for unknown reasons. (11) Some 317 million cubic feet of methane are stored in U.S. hydrates and some 49,000 quadrillion cubic feet exist in the world compared with known U.S natural gas reserves of ("only") 187 million cubic feet. (12) World stores are 10 million teragrams of trapped methane V.S. 5000 teragrams in the atmosphere). Enormous quantities of methane molecules are trapped in cage like structures with water molecules on the ocean floor. Seismic shifts have been known to release large amounts of methane.

For example, a deadly cloud of dissolved carbon dioxide and methane gas was released from Lake Nyos, Cameroon, in East Africa, which killed 1700 people, by a convective "magmatic" eruption which displaced the lower layer of the stratified lake in a volcanically active basin. However, methane may be primarily formed by bacterial degradation of on vegetation. (13) Life cycles for these gases are shown below, including long-lasting nitrous oxide, which since 1940 has increased from 0.5% to 1.2% in the atmosphere, primarily from microbial action on vegetation. (14)

                                        Gas Life Cycles (Figure VIII)

            GAS                20 YEARS            100 YEARS           500 YEARS     AVERAGE


Carbon Dioxide                ---                          ---                           120                   120                 

Methane                            56                       19-43                         9-16               12-18

Nitrous Oxide                  290                         320                          130                  120


The relative heat retention characteristics of each of these gasses is adjusted for effectiveness in Figure IX.

The significance of these data is that the relatively long decline, and the long life, of carbon dioxide in the atmosphere is not consistent with abrupt periods of rise and fall in 200 year warm-period cycles over the last 5000 years. The warm cycles should be expected to last much longer, since carbon dioxide, a chemically stable gas, persists for much longer periods.

The Solar Cycles

NASA data indicate that the climate on Mars is the warmest in decades, the planet's polar ice cap is shrinking, the ice in lower latitudes has disappeared, and a Martian ice age may be terminating. (15) This phenomenon appears to involve solar radiation, which has been increasing for the last 100 years. Without solar radiation, both Mars and the earth's temperature would be - 454 C. (16) and no other energy source exists in our solar system of this magnitude. As solar radiation varies in intensity, it can be expected to periodically also warm the earth's oceans, releasing dissolved carbon dioxide and melting methane hydrates -- the release of which have always accompanied all previous warming periods for millions of years. These greenhouse gasses then are known to absorb additional heat from the sun to cause follow-on periodic warming episodes, a secondary or derivative effect.

Five radiation cycles have been identified which operate independently of each other, (17) occasionally reinforcing each other, and occasionally canceling each other's effects (Figure X).


A 100,000-year cycle results from the elliptical orbit of the earth around the sun. A 41,000-year (obliquity) cycle results from the tilt of the earth on its axis. A 23,000-year (precession) cycle results from changes in direction of the earth's axis relative to the sun. Also, 95,000, 125 000 and 400,000 (obliquity) year cycles are operative, as is an 11-year sunspot cycle. All of these appear now to have peaked or are in decline. Over the last 300 years, following the Maunder "little ice age" there have been other dips in radiation (Figure (XI), but on average, radiation has increased. (18) This increase in radiation has been concurrent with the most recent warming period, which appears now to have been interrupted, in spite of accelerated burning of fossil fuels. 
Dr. H. Abdussamatov, head of the  St. Petersburg Pulkova Astronomical Observatory (operating since 1839), points out that the earth now has hit its temperature ceiling and that solar radiation has begun to fall, which possibly could account for the current cessation of  greenhouse gas emissions since 1988. He anticipates that a cooling period may now develop, and equipment currently is being installed in the Space Station to monitor this effect.


The earth has been subjected to many warming and cooling periods over millions of years, none of which were of human origin. Data from many independent sources have mutually corroborated these effects. They include data from coring both the Antarctic ice cap and sediments from the Sargasso Sea, from stalagmites, from tree rings, from up-wellings in the oceans, and from crustaceans trapped in pre-historic rock formations.

The onset of each 100,000-year abrupt warming period has been coincident with emissions into the atmosphere of large amounts of both carbon dioxide and methane greenhouse gases, which absorb additional heat from the sun, a secondary warming effect. Solar radiation would appear to be the initial forcing event in which warming oceans waters release dissolved carbon dioxide, and melt methane hydrates, both of which are present in the oceans in vast quantities. Subsequent declines in radiation are associated with long cooling periods in which the green house gases then gradually disappear (are re-absorbed) into terrestrial and ocean sinks, as reflected in the data from coring the Antarctic Ice Cap and Sargasso Sea.

The current 100 year solar radiation cycle may now have reached its peak, and irradiation intensity has been observed to be declining. This might account for the very recent net cessation of emission of green house gases into the atmosphere starting about 1988, in spite of increasing generation of anthropomorphically-sourced industrial-based green house gases.

While it seems likely that solar radiation, rather than human activity,  is the "forcing agent" for global warming, the subject surely needs more study.

Dr. D. Bruce Merrifield is a former Undersecretary of Commerce for Economic Affairs and Professor Emeritus of the Wharton School of Business at the University of Pennsylvania.  He holds Masters and Doctoral degrees in physical organic chemistry and currently is a member of the Visiting Committee for Physical Sciences at the University of Chicago.


1.  Science, August 26, (2005); Science Feb. 28 (1997) pp1267; Science News, Feb3, (2007) Vol. 171, pp67; Science Vol. 312, June 9 (2006) pp1485-89. http://www.Skymetrics.US/background/glossey.php -21k

2.   Science, June 6, (2006) pp1454; A.V. Federov, P.S. Dekens et al, The Pliocene Paradox, Science, Vol. 312, June 9, (2006) pp1485-89; D.R. MacAyeal, Dept. Geophysical Sciences, Univ. of Chicago,           

3.   Kenneth Clark, Civilization, Harper and Row, (1969), pp33; Arthur B. Robinson, Noah E. Robinson, Science (1996); L.D. Keigwin, The Little Ice Age and Medieval Warm Period in the Sargasso Sea, Science, Vol. 274, Nov. 29, (1996) pp 5292;

4.   The End of Angkor, Science, Vol. 311, March 10, (2006).

5.   Gerald Dickens, A Methane Trigger for Rapid Warming?, Science, Vol 299, Feb. 14, (2003); Seth  Borebstein, Methane A New Climate Threat, Nature, ; C. Frankenberg, J.F. Meirink et al. Assessing Methane ; C. Frankenberg, J.F. Meirink et al. Assessing Methane Emissions From Global Space-Borne Observations, Science, Vol. 308, May 13, (2005).

6.   Charles Higham, Civilization of Angkor; pp14-16

7.   Methane Since 1684, Climate and Environmental Physics, Physics Inst of Bern, Sidlerstrassa  5, Switzerland. 

8.   Hudson Canyon Map:; Wallace Broeker et al. Earth Observatory, Columbia Univ. Lecture at Amer Geographic Society, Baltimore, Spring 1999.

9.   Severinghouse, Science, Vol. 286, Oct. 29 (1999) pp 930-4.

10.   D.F. Ferretti, J.B. Miller et al, Unexpected Changes to the Global Methane Budget over the Past 2000 Years, Science, Vol. 309, Sept. 9 (2005).

11.   Mysterious Stabilization of Atmospheric Methane May Buy Time in Race
to Stop Global Warming, Geophysical Research Letters, Nov. 23 (2006). Mysterious Stabilization of Methane, Scientific American, Nov. 21 (2006).

12.   C&EN, Aug 8, (2005) pp16

13.   Science, Feb 28 (1997) pp1267; Geothermal Geophysical, Geosystems Vol. 10 (2001) pp1029.

14.   I.S.A. Isakreacta, et al, Radiation Forcing of Climate, Inter-Government Panel on Climate Change (2003).

15.   Urban Renaissance Inst., http://www.; Eva Bauer, Martin
Clausen, V. Broukin, Geophysical Research Letters, Vol. 30, No. 6 (2003) pp127 

16.   Milankovitch Cycles - Wikipedia Encyclopedia

17.   Richard Mueller, Gordon MacDonald (1977) Glacial Cycles and Astronomical Forcing

18.   J. Howard Maccabee,, (colloquium)
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