All data points to the sun as the primary source of short-term and long term climate change on Earth. While volcanic eruptions such as the current one in Iceland can affect short-term weather conditions over a region, planetary climate is governed by solar activity-or lack of it.
The first inkling that something had changed with the sun was the recognition of an abnormal sunspot cycle. Then, astronomers noted that all the planets were heating up-even little Pluto on the outskirts of our solar system.
While climatologists on Earth massaged the data to make it seem like man-made global warming was real, major climate changes were occurring on Mars.