But recent research suggests that solar fluctuations, while small, may affect climate by driving the multi-decadal switch from El Niño to La Niña conditions in the Pacific Ocean.
Other research finds that our inability to correctly simulate the cooling La Niña cycle is a major reason that computer climate models run hot.
La Niña is the cool phase of the El Niño – Southern Oscillation (ENSO), a natural cycle that causes temperature fluctuations and other climatic effects in tropical regions of the Pacific.
The familiar El Niño and La Niña events, which last for a year or more at a time, recur at irregular intervals from two to seven years.
Serious effects of ENSO range from catastrophic flooding in the U.S. and Peru to severe droughts in Australia.
The sun has several natural cycles, the most well known of which is the 11-year sunspot cycle.
During the sunspot cycle the sun’s heat and light output waxes and wanes by about 0.08%.
Although this variation in itself is too small to have any appreciable direct effect on the earth’s climate, indirect solar effects can have an impact on the warming and cooling of our planet –
indirect effects that are ignored in climate models.
Just such an indirect solar effect may have been discovered in a new study revealing a correlation between the end of sunspot cycles and the switch from El Niño to La Niña states of the tropical Pacific.
The research was conducted by a team of scientists from NASA and the U.S. National Center for Atmospheric Research.
The researchers found that the termination of all five solar cycles between 1960 and 2010-11 coincided with a flip from a warmer El Niño to a cooler La Niña.
And the end of the most recent solar cycle, which has just occurred, also coincides with the beginning of a new La Niña event.
Because the end of the 11-year solar cycle is fuzzy, the research team relied for its “clock” on the sun’s more well-defined magnetic polarity cycle known as a Hale cycle, which is precisely 22 years in length.
The correspondence between the 11-year solar cycle and the onset of La Niña events is illustrated in the figure below, showing the six-month smoothed monthly sunspot number since 1950 in black and the Oceanic El Niño Index in color.
The red and blue boxes mark El Niño and La Niña periods, respectively, in the repeating pattern.
What stands out is that the end of each sunspot cycle is closely correlated with the switch from El Niño to La Niña.
That the correlation is mere coincidence is statistically highly unlikely, say the study authors, although further research is needed to establish the physical connection between the sun and earth responsible for the correlation."