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	It's the sun
	Climate's changed before
	There is no consensus
	It's cooling
	Models are unreliable
	Surface temp is unreliable
	Ice age predicted in the 70s
	We're heading into an ice age
	Al Gore got it wrong
	It hasn't warmed since 1998
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• A Great Science Fiction Writer Passes - Goodbye Dr. Crichton
• Is Antarctic ice melting or growing?
• Does Urban Heat Island effect add to the global warming trend?
• The link between hurricanes and global warming
• Arctic sea ice melt - natural or man-made?
• A new twist on mid-century cooling
• April update on global cooling 2008
• Is Pacific Decadal Oscillation the Smoking Gun?
• Can animals and plants adapt to global warming?
• Did global warming stop in 1998?
• Do cosmic rays cause clouds?
• Cartoon about global warming alarmism
• La Nina watch: March update
• The Mystery of the Vanishing Ocean Heat
• Global warming stopped in 1981... no, wait! 1991!
• Determining the long term solar trend
• Comparing IPCC projections to observations
• Climate change on Mars
• Global cooling: the new kid on the block
• What 1970s science said about global cooling
• Has solar cycle 24 begun?
• Empirical evidence for positive feedback
• Al Gore and Dr Thompson's thermometer
• Does model uncertainty exagerate global warming projections?
• Are we heading into a new Little Ice Age?
• Did global warming cause Hurricane Katrina?
• What does CO2 lagging temperature mean?
• Svensmark and Friis-Christensen rebut Lockwood's solar paper
• Evaporating the water vapor argument
• They predicted an ice age in the 70's

It's Solar Cycle Length

What the science says...

While solar cycle length (SCL) doesn't directly affect Earth's climate, it is a useful proxy for long term changes in solar activity. Eg - when the sun gets hotter, SCL is shorter. When the sun shows a cooling trend, SCL is longer.

Errors in Friis-Christensen and Lassen's 1991 study

The problem with Friis-Christensen and Lassen's 1991 graph is their solar cycle data consists of two incongruous sets of physical data (Laut 2003). The first 20 points of the graph are smoothed using a 1-2-2-2-1 running average. However, the last 4 points (marked 1 to 4 in the figure below) are not filtered in the same manner. Points 1 and 2 are only partially filtered. Points 3 and 4 are not filtered at all. In effect, it's like marrying two separate sets of data.

Lassen updates his solar cycle data

In 1999, Lassen updated his graph with newer data, now able to filter the later solar cycles (Lassen 1999). His conclusion: “It has previously been demonstrated that the mean land air temperature of the Northern hemisphere could adequately be associated with a long-term variation of solar activity as given by the length of the approximately 11- year solar cycle. Adding new temperature data for the 1990’s and expected values for the next sunspot extrema we test whether the solar cycle length model is still adequate. We find that the residuals are now inconsistent with the pure solar model. We conclude that since around 1990 the type of Solar forcing that is described by the solar cycle length model no longer dominates the long-term variation of the Northern hemisphere land air temperature.”

Lassen 1999 - the top figure compares temperature to solar cycles with the correlation breaking down in the mid 1970's. This is highlighted in the bottom figure, plotting the difference between temperature and solar cycle length.

Other studies on solar cycle lengths

Other studies confirm Lassen's later conclusion:

• Kelly 1992 models the effects of a combination of greenhouse and solar-cycle-length forcing and compare the results with observed temperatures. They find that "even with optimized solar forcing, most of the recent warming trend is explained by greenhouse forcing".
• Laut 1998 analyses the period 1579–1987 and finds "the solar hypothesis—instead of contradicting—appears to support the assumption of a significant warming due to human activities.
• Damon 1999 uses the pre-industrial record as a boundary condition and finds the SCL-temperature correlation corresponds to an estimated 25% of global warming to 1980 and 15% to 1997.
• Benestad 2005 concludes "There have been speculations about an association between the solar cycle length and Earth's climate, however, the solar cycle length analysis does not follow Earth's global mean surface temperature. A further comparison with the monthly sunspot number, cosmic galactic rays and 10.7 cm absolute radio flux since 1950 gives no indication of a systematic trend in the level of solar activity that can explain the most recent global warming."

Solar cycle length as a proxy for long term solar activity tells us solar variations have had very little contribution to global warming since 1975. More on the sun's impact on global warming...