Assuming there is global warming, what is its cause?

Is solar activity more determinative of climate change than man-made “greenhouse” gases?

In 2007, cosmotologists began to look to a 1976 study of Eddy concerning the fluctuating activity of sunspots, and particularly the low sunspot period of the mini-ice age known as the Maunder Minimum, for an alternative explanation of global warming which had been attributed to man-made “greenhouse gases.”

Introduction

Man-made carbon dioxide is generally thought to produce global warming. However, in a recent article entitled “Does Carbon Dioxide Drive Global Warming?” I presented several major reasons why carbon dioxide is probably not the primary cause.1 But if carbon dioxide is not the cause, then what is? Evidence is accumulating that cosmic rays associated with fluctuations in the sun’s electromagnetic field may be what drives global warming. A new theory called cosmoclimatology that proposes a natural mechanism for climate fluctuations has been developed by Henrik Svensmark,2 Head of the Center for Sun-Climate Research at the Danish National Space Center.

Some History

Edward L. Maunder reported in 1904 that the number of spots on the sun has an 11-year cycle.3 Sunspots can be observed in real time online at www.spaceweather.com. Figure 1 shows a 400-year record of the monthly number of sunspots. Note the low number of sunspots in the period from 1645 to 1715. This period is called the Maunder Minimum4 and coincides with the Little Ice Age, the coldest period of temperature during the last 1,000 years.

For many years, climatologists attempted to correlate the number of sunspots with various climate variables, including temperature and precipitation. By the 1980s these attempts were determined to be futile, because the percentage change in solar heating was found to be insufficient to explain the variations. However, this interest began to increase the connection between cosmic rays and sunspots, carbon-14 in the atmosphere, beryllium-10 on the surface of meteorites, and other processes. In particular, it was found that carbon-14 dating needed to be corrected for fluctuations in cosmic ray flux. Without such adjustments, many carbon-14 dates were inconsistent. The question was raised, could cosmic rays affect other geophysical phenomena as well?

A New Climate Theory

In 1995, Henrik Svensmark discovered a startling connection between the cosmic ray flux from space and cloud cover. He found that when the sun is more active–more sunspots, a stronger magnetic field, larger auroras, stronger solar winds, etc.–fewer cosmic rays strike the earth and cloud cover is reduced, resulting in warmer temperatures. Figure 2 shows the relationship he found between low-level cloud amount derived from satellite data from the International Satellite Cloud Climatology Project and cosmic ray counts from Climax, Colorado.

It is evident in Figure 2 that for the 22-year period from 1983 to 2005, the average amount of low-level cloud follows the flux of cosmic rays very closely. In fact, Svensmark claims that the correlation coefficient is 0.92, a very high correlation for this type of data. In addition, when looking at various longer periods of record using proxy data for these two variables, he also found good correlations and similar trends. In particular, he suggested that during the Little Ice Age when the sun was inactive, cosmic ray flux from space was high, cloud amount was greater, and global temperatures were cooler. As the sun became more active after 1750, cosmic ray flux decreased, cloud amount decreased, and global temperatures warmed. Svensmark proposed that the global warming we’ve experienced for the past 150 years is a direct result of an increase in solar activity and attendant warming.

A potential change in cloud cover of 3-4 percent caused by changes in cosmic ray flux is sufficient to explain global temperature changes of several degrees due to the change in the reflectivity of clouds. The reason the variation in direct radiation from the sun was rejected earlier is because it has been found to vary only by a few tenths of a percent. This is insufficient to explain observed global warming.

To read about the Svensmark’s experiments demonstrating how some portion of climate change is based on solar activity, click here.

Click next page to read about the Maunder Minimum’s climate-cooling effect.