... and what the sudden appearance of the latest one may teach us:
On the website The Blackboard, there is a plot of the latest sea surface temperature anomalies from the Hadley Center. It has jumped dramatically in just one month. The reason is clearly related to the 2009 El Niño which has developed quickly over the last several months as seen in the ECMWF ocean data (see).
The ECMWF vertical cross-sections (see, see, see and see) provide a useful perspective in that substantial cool (as well as warm) anomalies exist at depth. The El Niño signal is clear in the equatorial cross-section.
There are two messages in this data. First, the sudden development of this El Niño illustrates that it is dominated by ocean and atmospheric circulation changes, not an annual global average radiative forcing. Second, the regional variation in the patterning of heating further reinforces that climate is dominated by spatial variations in circulation features, and not a global-annual average surface temperature trend or other climate metric averaged on this space scale (see and see).
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