By Mike Johnson
Climate scientists are starting to realize how important the rhythmic switching from El Niño to La Niña in the South Pacific is to global warming – not in making the planet warmer, but rather distributing the surplus warmth we are creating by the burning of fossil fuels. The role of this southern oscillation, as it has been called, has been well explained and easy enough to find on Google.
In brief it works this way, and is caused by the movements of the trade winds: during the La Niña periods, warm water from the surface is carried by currents deep into the ocean. This has a cooling effect on surface air temperature, a warming effect on the ocean’s depths. During the rarer, El Niño episodes, this does not happen, the warm water sits on the surface and recorded air temperatures are thus higher. Given that 93% of the heat we are producingis absorbed by the oceans, the importance of the southern oscillation becomes clear.
Here are two graphs which sum up the known data.
Not being a scientist, and failing miserably at school maths I’m probably the best person to explain to people like me how to read these graphs. Begin with the O line four lateral lines up from the bottom. That O line represents the average temperature for the years 1961 to 1990. the other lateral lines represent temperature deviations from the average measured in fractions of a degree. This we have .01 above and -01 below, etc. The vertical bars represent those deviations from that average year by year. These are known as standard deviation graphs.
The first thing that strikes the eye is that 1985 was the last year in which the temperature dipped below the late 20th Century average. If you were born after that year you have never lived a year in which global temperatures fell below that average.
The next thing to strike the eye is that the red bars are generally taller than the blue and grey bars. The red bars represent the El Niño years, always hotter than the blue and mixed years. The blue bars, the La Niña years, are prominently represented in the cooler years before temperatures began to rise steeply in the 1980s. They grey bars are those mixed years with both La Niña and El Niño effects evident.
The last grey bar on the is 2013. A grey bar represents mixed years which are neither totally one or the other. 2013 was one such mixed year. Notice that 2011 (three bars from the right) was the hottest La Nina year on record, but appreciably cooler than 2010, the hottest year ever recorded and an El Niño year.
My prediction would be that next time we have a red, El Niño year, which we are due, we will break new global temperature records and bring a new crop of weather disasters. Forewarned is forearmed.
Here, the red and blue dots tell essentially the same story as the red and blue bars of the first graph using a modified time line.
Since these temperatures represent global averages, it is becoming clear that what happens with the trade winds and the southern oscillation in the South Pacific is important to our understanding of how the energy imbalance we are creating is playing out globally.