Sunspots

It is interesting that there is a correlation between sunspot activity and climate. Right now we are in a low in sunspot activity and global temperatures are cooler than the Global Warming models would predict. Here's a bit from a NASA site that tracks sunspot activity:

The Maunder Minimum

Early records of sunspots indicate that the Sun went through a period of inactivity in the late 17th century. Very few sunspots were seen on the Sun from about 1645 to 1715 (38 kb JPEG image). Although the observations were not as extensive as in later years, the Sun was in fact well observed during this time and this lack of sunspots is well documented. This period of solar inactivity also corresponds to a climatic period called the "Little Ice Age" when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes. There is evidence that the Sun has had similar periods of inactivity in the more distant past. The connection between solar activity and terrestrial climate is an area of on-going research.

Besides sunspots, there is a newly discovered Atlantic Multidecadal Oscillation that is expected to keep the world cooler than expected for the next decade.