Chapter 5 summarizes the research of a growing number of scientists who say variations in solar activity, not greenhouse gases, are the true driver of climate change. We describe the evidence of a solar-climate link and how these scientists have grappled with the problem of finding a specific mechanism that translates small changes in solar activity into larger climate effects. We summarize how they may have found the answer in the relationships between the sun, cosmic rays and reflecting clouds.

Chapter 5 Key Findings

• The IPCC claims the radiative forcing due to changes in the solar output since 1750 is +0.12 Wm-2, an order of magnitude smaller than its estimated net anthropogenic forcing of +1.66 Wm-2. A large body of research suggests that the IPCC has got it backwards, that it is the sun’s influence that is responsible for the lion’s share of climate change during the past century and beyond.

• The total energy output of the sun changes by only 0.1 percent during the course of the solar cycle, although larger changes may be possible over periods of centuries. On the other hand, the ultraviolet radiation from the sun can change by several percent over the solar cycle - as indeed noted by observing changes in stratospheric ozone. The largest changes, however, occur in the intensity of the solar wind and interplanetary magnetic field.

• Reconstructions of ancient climates reveal a close correlation between solar magnetic activity and solar irradiance (or brightness), on the one hand, and temperatures on earth, on the other. Those correlations are much closer than the relationship between carbon dioxide and temperature.

• Cosmic rays could provide the mechanism by which changes in solar activity affect climate. During periods of greater solar magnetic activity, greater shielding of the earth occurs, resulting in less cosmic rays penetrating to the lower atmosphere, resulting in fewer cloud condensation nuclei being produced, resulting in fewer and less reflective low-level clouds occurring, which leads to more solar radiation being absorbed by the surface of the earth, resulting (finally) in increasing near-surface air temperatures and global warming.

• Strong correlations between solar variability and precipitation, droughts, floods, and monsoons have all been documented in locations around the world. Once again, these correlations are much stronger than any relationship between these weather phenomena and CO2.

• The role of solar activity in causing climate change is so complex that most theories of solar forcing must be considered to be as yet unproven. But it would also be appropriate for climate scientists to admit the same about the role of rising atmospheric CO2 concentrations in driving recent global warming.

Chapter 5. Solar Variability and Climate Cycles (PDF, 648 kb)

     5.1. Cosmic Rays (PDF, 116 kb)

     5.2. Irradiance (PDF, 126 kb)

     5.3. Temperature (PDF, 222 kb)
            5.3.1. Global
            5.3.2. Northern Hemisphere
            5.3.3. North America
            5.3.4. South America
            5.3.5. Asia
            5.3.6. Europe
            5.3.7. Other

     5.4. Precipitation (PDF, 256 kb)
            5.4.1. North America
            5.4.2. South America
            5.4.3. Africa
            5.4.4. Asia
            5.4.5. Europe

     5.5. Droughts (PDF, 81 kb)

     5.6. Floods (PDF, 55 kb)

     5.7. Monsoons (PDF, 72 kb)

     5.8. Streamflow (PDF, 43 kb)