Correlation of global temperature with solar activity

The solar output is very nearly constant, as shown in the plot below. The range of variation is about 0.2%, so reproducible that it is often referred to as the "solar constant".

But there are other aspects of the Sun's activity that are not constant, as indicated by the changing sunspot activity.

An early indication that the Sun's variability in ways other than total output had something to do with climate was the "Maunder Minimum". The researcher Maunder found that during this cold period between 1645-1715 there was very little sunspot activity, and this discovery led to the naming of the phenomenon after him. It suggested that solar activity was coupled to climate and led to tabulations of sunspot number as an indication of solar activity. 太阳活动方式不同于总输出的变异性与气候有关的早期迹象是‘蒙德最低期’。研究者蒙德发现，在1645-1715年这一寒冷时期，太阳黑子活动非常少，这一发现导致了这一现象以他的名字命名。这表明太阳活动与气候有关，并促使对太阳黑子数进行统计，作为太阳活动的指示。

This illustration is a sketch of data from Durkin, based on data published by Friis-Christensen and Lassen. The end of the solar data has been altered in response to corrections of their data. This correlation between solar activity and temperature has been critiqued by Schneider and others, so it is an active area of investigation. The measured solar activity is well-correlated with the observed temperature variations, but does not follow the recent upturn in temperature as the originally published plot indicated.

While it appears that the measured solar cycle length tracks the temperature better than the CO₂ concentration for the twentieth century up to 1970, this presented data remains quite controversial. When you look at the climate models that seek to show the human influence past 1970, you do see a good correlation of the temperature with the projected CO₂ influence included, while the correlation with solar cycle length weakens.

The illustrations at left show the raw data for temperature and solar activity at the top, then that data with a 11 year running average to filter out the normal solar activity period. The middle graph suggests a correlation between solar activity and temperature, even though the peaks are offset. But when the last few years of data are included, the curves diverge and severely weaken the case for the driving of temperature by this measure of solar activity. These illustrations were prepared by Chris Merchant, School of GeoSciences, University of Edinburgh from the original data. 左边的示意图显示了温度和太阳活动的原始数据，顶部是原始数据，然后是加上11年运行平均值以滤波器去除正常太阳活动周期后的数据。中间的图表表明太阳活动与温度之间存在相关性，尽管峰值有所偏移。但当包含最后几年的数据时，曲线开始分离，并严重削弱了太阳活动这一指标对温度驱动作用的论点。这些示意图由爱丁堡大学地质科学学院的Chris Merchant制作，基于原始数据。

The above illustration from Wikipedia shows some of the solar measurements as a function of time. The dominant fact from that illustration is that the overall solar output is incredibly constant -- varying only about one part in 1366! But the other variables are measured on a relative scale and represent much larger percentage variations, so it is possible that the solar flare index and the sunspot observations are windows to subtle influences on the Earth's climate that we don't understand.

Another solar activity correlation that is being investigated is that with cosmic radiation and its possible effect on cloud nucleation.