This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.
Objection:
The sun is the source of all the warmth on earth. Any increase in temperature is most likely due to changes in solar radiation.
Answer:
It’s very true that the earth is warmed, for all practical purposes, entirely by solar radiation. So if the temperature is going up or down a reasonable place to find the cause would be the sun. Well, it turns out that it is more complicated than one might think to detect and measure changes in the amount or type of sunshine reaching the earth. Detectors on the ground are too susceptible to all kinds of interference from the atmosphere. After all, one good cloud passing overhead can cause an instant shiver on an otherwise beautiful, warm day, but not because the sun itself changed. The best way to detect changes in the actual output of the sun versus changes in the radiation reaching the earth’s surface because of clouds, smoke, dust or pollution is by taking readings from space.
This is a job for satellites. According to PMOD at the World Radiation Center there has been no increase in solar irradiance since at least 1978 when satellite observations began. This means that for the last thirty years, while the temperature has been rising fastest, the sun has shown no trend.
There has been work done on reconstructing the solar irradiance record over the last century before satellites were available. According to the Max Plank Institute where this work is being done, there has been no increase in solar irradiance since around 1940. This reconstruction does show an increase in the first part of the 20th century that coincides with the warming from around 1900 til the 1940′s. This trend in irradiance is not enough to explain it all, but it is responsible for a large portion of that trend in temperature. See this chart of the observed temperature, the modelled temperature and the variations in the major forcings that contributed to 20th century climate.
Real Climate has also done a couple of detailed discussions both about what the conclusions about solar forcing are, as well as exactly how they were arrived at. Read them here and here.
This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.
“It’s the Sun, Stupid” was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.