By Andy May
According to Javier and the IPCC total solar radiation output varies little, less than 0.1%. This is only 0.7 to 1.4 Watts/m2 and converted to incident radiation striking the Earth this is reduces to about 0.05 to 0.4 W/m^2. The latter values can be compared to an IPCC anthropogenic effect estimate of 2.3 Watts/m2 . They believe it has a small effect on the Earth’s climate. Others, like Abdussamatov, think solar output is more variable, perhaps varying 3 Watts/m2 (their Figure 3). Other variable stars, similar to the sun, seem to have 3% dimming in their minima, which is certainly significant. Both of the latter two examples are larger than the IPCC estimate of man’s influence. We don’t want to get any further into this debate here other than to note the IPCC may be significantly underestimating the effect of solar and ocean cycles in their models. The key point is we don’t know what drives the Earth’s climate. There are a bewildering number of natural and man-made factors that influence it.
While variations in total solar irradiance (TSI) may be small, there is clear evidence that Earth/solar cycles affect our climate. This is discussed in detail by two well referenced posts by Javier here and here. While measured TSI variations are small, the solar UV (ultraviolet) output varies by up to 10%, this affects ozone heating in the stratosphere which may have an influence on the troposphere. The varying UV radiation from the sun and other solar impacts on climate are discussed by Dr. Isaac Held and others at an NRC workshop here.
An interesting quote from the NRC (National Research Council) workshop in 2013:
“In recent years, researchers have considered the possibility that the sun plays a role in global warming. After all, the sun is the main source of heat for our planet.”
They follow this by explaining that solar influence is regional, how exactly does that work? The sun is 109 times larger in diameter than the Earth and 93,000,000 miles away, how can its influence be regional? The Pacific Ocean covers almost one third of the Earth’s surface and 68% of the landmass is in the northern hemisphere; so changes in the surface that the solar radiation hits are bound to cause uneven warming in the short (hundreds or thousands of years) term. As they correctly note, solar changes and regional surface variations cause changes in precipitation and in air circulation. Uneven warming can be expected to do this. However, an uneven warming effect does not disprove solar-caused global warming. It just means global warming of a heterogeneous surface cannot occur evenly everywhere instantaneously. The main means of heat distribution are through water phase changes, that is evaporation, circulation and precipitation. The adjustment of the Earth’s surface to a change in solar activity takes a long time, thus we have long term ocean cycles like the 1,500-year cycle.