The folks who think that the sun is the principle determinant of climate have an interesting forecast based on the number of sunspots in each solar cycle. This chart shows the historic pattern, and based on the duration of past cycles, they predict ahead a few years. Basically they are saying that the average solar cycle is 10.7 years, but those preceding and during the Dalton Minimum were about 13 years. The current cycle (24) should have started in 2007, but is just now getting under way.
A low number of sun spots correlates well with lower than average global temperatures. The Year Without a Summer, in 1816, occurred during the Dalton Minimum.
The chart runs from 1700 to 2025 in 20-year tick marks. "Projected" starts in 2007, the date of the report in May, 2007, when they said the next cycle was at least one year away. In fact, we now know it was more than two years away. The original reference is
About a year ago, a NASA solar scientist agreed that we may be in for another Dalton Minimum. However, the current sun-spot cycle has started out aggressively and we initially went to 75 spots which was considered the peak for a minimum cycle. It later subsided to 17 spots. (see current number in gadget in the upper right corner of this page)
The Wikipedia article on Solar Variation is a bit more conservative. There are several different superimposed cycle lengths in the "solar cycle." Quoting Damon and Scott (1989)*, the following forecasts are possibilities:
| Cycle length | Cycle name | Last positive 14C anomaly | Next "warming" |
| 2241 | Landscheidt | AD 1400 (cool) | AD 2520 |
| 232 | --?-- | AD 1922 (cool) | AD 2038 |
| 208 | Suess | AD 1898 (cool) | AD 2002 |
| 88 | Gleisberg | AD 1986 (cool) | AD 2030 |
* "Solar Variability: climatic change resulting from changes in the amount of solar energy reaching the upper atmosphere.". Introduction to Quaternary Ecology http://www.geo.arizona.edu/palynology/geos462/20climsolar.html
The 2002 "warming" wasn't detectable or ran late. Maybe 2030 will be another major upswing. Meanwhile, we should have some warming, then cooler weather in the usual (approximately) 13-year cycles.
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