By Joe D'Aleo
Monday, August 3, 2009
As we have in recent stories, noted that high latitude volcanoes produce this summer cooling over the United States by favoring higher latitude blocking.
June was cool across the north.
It spread south in July.
On a larger scale and longer term, more major eruptions tend to lead to global cooling while extended periods of low activity warming. This is because volcanic aerosols reflect solar radiation back to space, reducing the amounts of solar energy reaching the surface. An anomalously clean atmosphere allows more solar heating.
The high volcanic aerosol content in the early 1980s with Mt St Helens and El Chichon and the early 1990s with Pinatubo and Cerro Hudson produced cooling for several years.
The record low levels of aerosols (NASA GISS Sato Index) in the late 1990s though the mid 2000s may have contributed to the warmth.
In addition, the other spikes and dips are clearly seen associated with El Ninos (Warming) and La Ninas (cooling).
With the recent volcanic activity, low solar, and a two year La Nina, we are seeing a return to temperature levels at the start of the satellite monitoring era.
You can see that cooling clearly since 2002.