Watt about ENSO?

One of the recent Watts Up With That posts is by Bob Tisdale and is titled A different perspective of the equatorial pacific and ENSO events. ENSO is the El Niño – Southern Oscillation. I’m no expert at this, but this seems to be a periodic oscillation in the sea surface temperatures in the Pacific, typically with a period of about a year. The strength of the oscillation is indicated by what is called the Southern Oscillation Index (SOI) which also indicates if it is in a warm-phase (El Niño) or a a cool-phase (La Niña). The figure below (taken from the Wikipedia page on ENSO) shows changes in the SOI from 1876 till 2011.

Southern Oscillation Index time series from 1876-2011.

Southern Oscillation Index time series from 1876-2011.

There are many who suggest that although ENSO correlates well with short-term global temperatures, it is unable to explain the long-term warming trend. In other words, ENSO is a series of perturbations on top of a signal that has a long-term rising trend. Bob Tisdale claims that this is a myth. You may argue that since I’ve acknowledged that I am no expert on ENSO, that I should refrain from commenting. There is, however, something that I have learned in the 20 or so years that I have been an active scientist, and that is that there are a few fundamental conditions that all models need to satisfy. These are conservation of energy, conservation of linear momentum, and conservation of angular momentum (plus conservation of mass, if I was being pedantic). It doesn’t really matter how complex or detailed a model is, if it doesn’t satisfy these conservation laws there is a problem. The figure below (which I found on the Skeptical Science website) shows the change in the Earth’s total heat content. Most of the energy is going into the Oceans and this figure indicates that the total amount of heat/energy has been rising since 1970 and that there is > 2 x 1023 J more energy in the system than there was in 1970.

Change in Ocean and Land heat content since 1960.

Change in Ocean and Land heat content since 1960.

Here’s the questions that I have. Is the above figure essentially correct? If not, what is wrong with it? If it is correct and if all the warming we’ve been seeing for the last 40 – 50 years is due to ENSO, how does an oscillation with a period of maybe a year lead to a rising trend that has existed since about 1970? Where is the energy coming from? ENSO cannot generate energy, it can only move it around. I can see how an oscillation could change the energy balance for a short while, but I have trouble seeing how – at the end of an oscillation – there can be a net increase (or decrease) in energy. I’d be interested to hear Bob Tisdale explain how a short-period oscillation can lead to a long-term warming trend. Of course, there could simply be some other long-term oscillation. However, this would need to have a period greater than 100 years in order to explain a 40-year rising trend. Also, if such an oscillation exists, what is it? Furthermore, what physical process is leading to the heat content continuing to rise since 1970? Ideally the Earth should settle towards some kind of equilibrium state in which the amount of energy it gains is balanced by the amount of energy it loses. If the heat content has been essentially rising for 40 years, we need some process that – despite rising temperatures – is resulting in us preferentially losing less energy than we gain. The obvious one to me is rising CO2 levels in the atmosphere, but I’d be happy to hear someone give a viable alternative.

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