Solar activity & climate: is the sun causing global warming?
What the science says...
As supplier of almost all the energy in Earth's climate, the sun certainly has a strong influence on climate change. Consequently there have been many studies examining the link between solar variations and global temperatures.
The correlation between solar activity and temperature
The most commonly cited study by skeptics is a study by scientists from Finland and Germany that finds the sun has been more active in the last 60 years than anytime in the past 1150 years (Usoskin 2005). They also found temperatures closely correlate to solar activity.
However, a crucial finding was the correlation between solar activity and temperature ended around 1975. At that point, temperatures rose while solar activity stayed level. This led them to conclude "during these last 30 years the solar total irradiance, solar UV irradiance and cosmic ray flux has not shown any significant secular trend, so that at least this most recent warming episode must have another source."
You read that right. The study most quoted by skeptics actually concluded the sun can't be causing global warming. Ironically, it's the sun's close correlation with Earth's temperature that proves it has little to do with the last 30 years of global warming.
Measurements of solar activity
This is confirmed by direct satellite measurements that find no rising trend since 1978, sunspot numbers which have leveled out since 1950, the Max Planck Institute reconstruction that shows irradience has been steady since 1950 and solar radio flux or flare activity which shows no rising trend over the past 30 years.
Other studies on solar influence on climate
This conclusion is confirmed by many studies quantifying the amount of solar influence in recent global warming:
Ocean Thermal Inertia
Solanki also found that over 1150 years, temperature lagged solar activity by 10 years. Eg - presumably due to ocean thermal inertia, it took Earth's climate 10 years to catch up to changes in solar activity. This is exactly what's observed in the 20th century - in the early decades, solar activity rose sharply with temperature lagging a decade behind. When solar activity leveled out in the 40's, so too did global temperatures.
|© John Cook 2007|