Email, Katharine Hayhoe, associate professor, Public Administration, director, Climate Science Center, Texas Tech University, May 11, 2015
As a scientist, I would say false to “what causes the climate is the sun” and half-true to “what causes the climate TO CHANGE is the sun”. I realize the second quote is not what he said, but I think that might have been what he meant, so I’ll address both of them.
STATEMENT: “what causes the climate is the sun”
EXPLANATION: Google defines climate as "the weather conditions prevailing in an area in general or over a long period.” The sun shines on Mercury and on the moon, just as it does on the Earth. However, Mercury and the moon do not have any weather conditions, nor any climate -> because they do not have an atmosphere. So by this definition, the sun does NOT cause climate. It's having an atmosphere that causes a climate to exist. If a planet doesn’t have an atmosphere, it does not have a climate.
STATEMENT: “what causes the climate TO CHANGE is the sun”
EXPLANATION: Most of our energy comes from the sun. If the sun’s output goes down, in the absence of other factors that might be acting to counteract its influence, the Earth’s temperature would get cooler. If the sun’s output goes up, again if there are no other factors to counteract its influence, we get warmer.
The sun has certainly been responsible for climate change in the past. It is thought to have contributed to the Little Ice Age, for example: http://en.wikipedia.org/wiki/Maunder_Minimum#Little_Ice_Age
Lately, however, the sun’s energy has been decreasing since the mid-1970s. So, if the sun were the main driver for the Earth’s temperature change from the mid-1970s until now, we would be cooling. We aren’t though - we are warming. So although the sun has caused climate to change in the past, it is by no means the only factor that causes climate change, and in this case it is definitely not the dominant factor because we are warming instead of cooling.
The idea that the sun is driving climate change today is a very common myth - so common, that it is one of the 3 myths I address in my recent TEDx talk, starting at 7.25. Here is the link: https://youtu.be/PtrYNGs9oRM?t=7m24s