Isn’t climate change due to variations in the Sun’s output?
No. Although the Sun’s output does vary, its effect on global warming is about one tenth of that caused by mankind’s emission of greenhouse gases.
The primary source of energy providing heat to the Earth’s living organisms, atmosphere and oceans is the Sun. The amount of energy reaching the Earth’s surface depends on the output of the Sun, the Earth’s orbit around the Sun and effects in the atmosphere (both cloudiness and tiny particles emitted by man and volcanic eruptions). The Sun undergoes small (less than ±1 part in 2000) but significant variations in its intensity on an 11-year cycle and possibly underwent similar, longer term, changes in the distant past that cannot be measured directly. When the Sun is more active, as indicated by a greater number of sunspots on its surface, it emits more light and heat. However measurements have shown that the amount of heat reaching the Earth’s surface depends much more on the concentration of particles (aerosols) in the atmosphere than on the Sun’s activity. While there is evidence of a link between solar activity and some of the warming of the early 20th century, satellite measurements have shown that changes in the last 30 years cannot account for the recent rises in global temperatures. However, greenhouse gases can explain the rise; the warming attributable to mankind’s emissions of these gases is about ten times greater than that from changes in the Sun’s output.