Friday, September 14, 2012

El Nino, La Nina, and our Extreme Weather

U.S. Geological Survey reports that the drought we have experienced this last year is the worst that has occurred in the last 500 years, with water flow levels at close to half those of the drought years in the 1930's!  The USA just endured its third-hottest summer on record.  For the entire year to date, the US is having its warmest year since records began in 1895, reported by the National Climatic Data Center.   Arctic ice has shrunk to its lowest level on record.  

Why are some of our winters filled with rain and deep snow and others not?  Part of the answer come from examining natural changes in our atmosphere, ocean currents, and ocean temperatures. All parts of our ocean/air system are inextricably connected!  However the patterns found have proven difficult to predict and are not clearly understood.   British meteorologists were the first to notice in the 1920's that a strong rainy season in India usually occurred at the same time as droughts in Australia.

They observed a relationship between periods of high air pressure in the eastern Pacific Ocean and periods of low air pressure in the western Pacific. 
It was not until the mid twentieth century that fluctuations in ocean temperatures off the west coast of South America were called by the name “El Nino”

El Niño refers to one extreme in the oscillation cycle — with above-average sea surface temperatures in the central Pacific Ocean.  El Nino usually brings wetter winters  to central California.  It appears that El Nino conditions are forming at this time.  Hurrah!
The opposite stage in the cycle, La Niña, shows below-average sea surface temperatures in the central Pacific.

Another pattern that influences our winter weather in the U.S. is the Arctic Oscillation (AO), - a pattern in atmospheric pressure between the Polar Regions and the middle latitudes. The AO has a cold phase, which brings higher pressures over the Polar Regions and lower pressures over the middle latitudes; the warm phase brings the opposite conditions. The AO fluctuates on the order of weeks and months.  There also appears to be a link between the AO and Atlantic hurricanes.

But the extreme patterns that we are seeing doesn't seem to be explained by normal changes in atmospheric cycles.  Us humans are changing the nature of our own atmosphere!  One critical factor is the greenhouse effect caused by increasing CO2 in the air. 
In addition to visible light, sunlight also contains Infrared heat radiation.  This is the part of sunlight that we feel as heat on our skin.  Infrared coming from the sun is quite high frequency and can easily pass through glass and air. 

 When it is absorbed by dark colored material on earth – that warm material now serves as a heat source and radiates its own infrared heat– but as a heat source it is much cooler than the sun.  Cooler object radiate a frequency much longer wave than that from the sun... When it attempts to travel back out into space, it encounters the CO2 in the air like a mirror – and reflects  back to earth.  The more CO2 in the air the more infrared heat is reflected and trapped in our atmosphere.  This effect is well studied and beyond doubt. 

The concentration of CO2 in our atmosphere reached 395 parts per million by June 2012This current concentration is substantially higher than the 280 ppm concentration present in pre-industrial times, with the increase largely attributed to the burning of fossil fuels.  
 And still we have politicians who encourage us to burn more coal and drill more oil!

The graph below has been climbing much faster now than in the 1960s; despite some attempts to slow down emissions, the quantity of gas added to the atmosphere is doubling every 30-35 years

Level of CO2 in the atmosphere, 1958-2007 

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